View source for Ontology

{{Short description|Philosophical study of being}}
{{Distinguish|Oncology|Odontology|Ontogeny|Deontology}}
{{About|the philosophical study of being|the information science concept|Ontology (information science)}}
{{good article}}
'''Ontology''' is the philosophical study of [[existence|being]]. It is traditionally understood as the subdiscipline of [[metaphysics]] focused on the most general features of [[reality]]. As one of the most fundamental concepts, being encompasses all of reality and every [[entity]] within it. To articulate the basic structure of being, ontology examines the commonalities among all things and investigates their classification into basic types, such as the [[Theory of categories|categories]] of [[particular]]s and [[Universal (metaphysics)|universals]]. Particulars are unique, non-repeatable entities, such as the person [[Socrates]], whereas universals are general, repeatable entities, like the color ''green''. Another distinction exists between [[Abstract and concrete|concrete]] objects existing in [[space and time]], such as a tree, and abstract objects existing outside space and time, like the number 7. Systems of categories aim to provide a comprehensive inventory of reality by employing categories such as [[Substance theory|substance]], [[Property (philosophy)|property]], [[Relation (philosophy)|relation]], [[State of affairs (philosophy)|state of affairs]], and [[Event (philosophy)|event]].

Ontologists disagree regarding which entities exist at the most basic level. [[Platonic realism]] asserts that universals have objective existence, while [[conceptualism]] maintains that universals exist only in the mind, and [[nominalism]] denies their existence altogether. Similar disputes pertain to [[mathematical object]]s, [[unobservable]] objects assumed by scientific theories, and [[Ethics#Realism, relativism, and nihilism|moral facts]]. [[Materialism]] posits that fundamentally only [[matter]] exists, whereas [[Mind–body dualism|dualism]] asserts that [[mind]] and matter are independent principles. According to some ontologists, objective answers to ontological questions do not exist, with perspectives shaped by differing linguistic practices.

Ontology employs diverse [[Philosophical methodology|methods of inquiry]], including the analysis of [[Philosophical analysis|concepts]] and [[Phenomenology (philosophy)|experience]], the use of [[intuition]]s and [[thought experiment]]s, and the integration of findings from [[natural science]]. [[Formal ontology]] investigates the most abstract features of objects, while [[Applied ontology]] utilizes ontological theories and principles to study entities within specific domains. For example, [[social ontology]] examines basic concepts used in the [[social sciences]]. Applied ontology is particularly relevant to [[Information science|information]] and [[computer science]], which develop [[Ontology (information science)|conceptual frameworks of limited domains]]. These frameworks facilitate the structured storage of information, such as in a college database tracking academic activities. Ontology is also pertinent to the fields of [[logic]], [[theology]], and [[anthropology]].

The [[History of ontology|origins of ontology]] lie in the [[Ancient history|ancient period]] with speculations about the nature of being and the source of the universe, including ancient [[Indian philosophy|Indian]], [[Chinese philosophy|Chinese]], and [[Ancient Greek philosophy|Greek philosophy]]. In the modern period, philosophers conceived ontology as a distinct academic discipline and coined its name.

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== Definition ==
Ontology is the study of being. It is the branch of [[philosophy]] that investigates the nature of [[existence]], the features all entities have in common, and how they are divided into basic [[categories of being]].<ref>{{multiref | {{harvnb|Lowe|2005|p=[https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 671]}} | {{harvnb|Campbell|2006|pp=21–22}} | {{harvnb|Craig|1998|loc=Lead Section}} }}</ref> It aims to discover the foundational building blocks of the world and characterize [[reality]] as a whole in its most general aspects.{{efn|This focus on general principles rather than specific entities is traditionally expressed in the characterization of ontology as the science of ''being qua being'' or ''being insofar as it is being''.<ref>{{multiref | {{harvnb|Berto|Plebani|2015|p=1}} | {{harvnb|Shields|2014|pp=[https://books.google.com/books?id=A_pwEAAAQBAJ&pg=PA279 279–282]}} }}</ref>}} In this regard, ontology contrasts with individual sciences like [[biology]] and [[astronomy]], which restrict themselves to a limited domain of entities, such as living entities and celestial phenomena.<ref>{{multiref | {{harvnb|Berto|Plebani|2015|pp=1–3}} | {{harvnb|Campbell|2006|pp=21–22}} | {{harvnb|Effingham|2013|loc=§ The Basics: Ontology}} }}</ref> In some contexts, the term ''ontology'' refers not to the general study of being but to a specific ontological theory within this discipline. It can also mean an inventory or a [[conceptual scheme]] of a particular domain, such as [[Gene ontology|the ontology of genes]].<ref>{{multiref | {{harvnb|Simons|2009|pp=469–470}} | {{harvnb|Merriam-Webster|2024}} | {{harvnb|Campbell|2006|pp=21–22}} | {{harvnb|Haritha|Priyatharshini|Abishek|Kiran|2018|p=[https://books.google.com/books?id=LcpmDwAAQBAJ&pg=PA489 489]}} }}</ref> In this context, an inventory is a comprehensive list of elements.<ref>{{multiref | {{harvnb|Lowe|2006|p=[https://books.google.com/books?id=s7ISDAAAQBAJ&pg=PA195 195]}} | {{harvnb|Tambassi|2017|p=[https://books.google.com/books?id=dtYtDwAAQBAJ&pg=PA6 6]}} }}</ref> A conceptual scheme is a framework of the key concepts and their relationships.<ref>{{multiref | {{harvnb|Sankey|2018|loc=§ 1.7 Conceptual relativism}} | {{harvnb|Grove|Short|1991|p=[https://books.google.com/books?id=bLDsgZq849gC&pg=PA211 211]}} }}</ref>

Ontology is closely related to [[metaphysics]] but the exact relation of these two disciplines is disputed. A traditionally influential characterization asserts that ontology is a subdiscipline of metaphysics. According to this view, metaphysics is the study of various aspects of fundamental reality, whereas ontology restricts itself to the most general features of reality.<ref>{{multiref | {{harvnb|Berto|Plebani|2015|pp=3–4}} | {{harvnb|Lowe|2005|p=[https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 671]}} }}</ref> This view sees ontology as general metaphysics, which is to be distinguished from special metaphysics focused on more specific subject matters, like [[God]], [[mind]], and [[Value (ethics and social sciences)|value]].<ref>{{multiref | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 1. The Word 'Metaphysics' and the Concept of Metaphysics}} | {{harvnb|Craig|1998a|loc=§ 2. Specific Metaphysics}} }}</ref> A different conception understands ontology as a preliminary discipline that provides a complete inventory of reality while metaphysics examines the features and structure of the entities in this inventory.<ref>{{multiref | {{harvnb|Berto|Plebani|2015|pp=4–5}} | {{harvnb|Tambassi|2022|p=[https://books.google.com/books?id=JkCdEAAAQBAJ&pg=PA79 79]}} }}</ref> Another conception says that metaphysics is about real being while ontology examines possible being or the concept of being.<ref>{{harvnb|Jaroszyński|2018|p=6}}</ref> It is not universally accepted that there is a clear boundary between metaphysics and ontology. Some philosophers use both terms as synonyms.<ref>{{multiref | {{harvnb|Berto|Plebani|2015|pp=3, 5}} | {{harvnb|Mulligan|2012|p=[https://books.google.com/books?id=oLfwCAAAQBAJ&pg=PR10 x]}} }}</ref>

The etymology of the word ''ontology'' traces back to the [[ancient Greek]] terms {{lang|grc|ὄντως}} ({{Lang|grc-latn|ontos}}, meaning {{Gloss|being}}) and {{lang|grc|λογία}} ({{Lang|grc-latn|logia}}, meaning {{Gloss|study of}}), literally, {{Gloss|the study of being}}. The ancient Greeks did not use the term ''ontology'', which was coined by philosophers in the 17th century.<ref>{{multiref | {{harvnb|Berto|Plebani|2015|p=1}} | {{harvnb|Taliaferro|Marty|2018|p=[https://books.google.com/books?id=_5ZBDwAAQBAJ&pg=PA203 203]}} | {{harvnb|Hoad|1993|p=323}} }}</ref>

== Basic concepts<!--'Eleatic principle' redirects here--> ==
=== Being ===
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|footer            = The scope of ontology covers diverse entities, including everyday objects, living beings, celestial bodies, ideas, numbers, and fictional creatures.
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Being, or [[existence]], is the main topic of ontology. It is one of the most general and fundamental concepts, encompassing all of [[reality]] and every [[entity]] within it.{{efn|When used as a countable noun, ''a being'' is the same as ''an entity''.<ref>{{harvnb|Lowe|2005a|p=84}}</ref>}} In its broadest sense, being only contrasts with non-being or nothingness.<ref>{{multiref | {{harvnb|MacIntyre|2006|p=527}} | {{harvnb|Jaroszyński|2023|pp=[https://books.google.com/books?id=LtL7EAAAQBAJ&pg=PA254 254–255]}} | {{harvnb|Lowe|2005a|p=84}} | {{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PA1 1–2, 12–13]}} }}</ref> It is controversial whether a more substantial analysis of the concept or meaning of being is possible.<ref>{{multiref | {{harvnb|MacIntyre|2006|pp=528–529}} | {{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PA1 1–2, 12–13]}} }}</ref> One proposal understands being as a property possessed by every entity.<ref>{{multiref | {{harvnb|MacIntyre|2006|pp=528–529}} | {{harvnb|Casati|Fujikawa|loc=§ 2b. Universalism}} }}</ref> Critics argue that a thing without being cannot have properties. This means that properties presuppose being and cannot explain it.<ref>{{multiref | {{harvnb|Nelson|2022|loc=§ 1. Frege and Russell: Existence Is Not a Property of Individuals}} | {{harvnb|Casati|Fujikawa|loc=§ 1. Existence as a Second-Order Property and Its Relation to Quantification}} }}</ref> Another suggestion is that all beings share a set of essential features. According to the '''Eleatic principle''',<!--boldface per WP:R#PLA--> "power is the mark of being", meaning that only entities with [[Causality|causal]] influence truly exist.<ref>{{harvnb|Campbell|2006|p=22}}</ref> A controversial proposal by philosopher [[George Berkeley]] suggests that all existence is mental. He expressed this [[immaterialism]] in his slogan "to be is to be perceived".<ref>{{multiref | {{harvnb|Van Inwagen|2024|p=280}} | {{harvnb|Deutscher|2021|p=[https://books.google.com/books?id=IQ0mEAAAQBAJ&pg=PA20 20]}} }}</ref>

Depending on the context, the term ''being'' is sometimes used with a more limited meaning to refer only to certain aspects of reality. In one sense, being is unchanging and permanent, in contrast to becoming, which implies change.<ref>{{multiref | {{harvnb|MacIntyre|2006|p=527}} | {{harvnb|Zhang|2011|p=[https://books.google.com/books?id=Vl4EEAAAQBAJ&pg=PA220 220]}} | {{harvnb|Hartmann|2012|pp=[https://books.google.com/books?id=4PyJfVZn-rcC&pg=PA46 46–47]}} }}</ref> Another contrast is between being, as what truly exists, and [[Phenomenon|phenomena]], as what appears to exist.<ref>{{harvnb|MacIntyre|2006|p=527}}</ref> In some contexts, being expresses the fact that something is while [[essence]] expresses its [[Quality (philosophy)|qualities]] or what it is like.<ref>{{multiref | {{harvnb|Lowe|2005a|p=84}} | {{harvnb|Ceylan|1993|p=[https://www.jstor.org/stable/20840134 329]}} }}</ref> 

Ontologists often divide being into fundamental classes or highest kinds, called ''[[categories of being]]''.<ref name="Thomasson2022">{{multiref | {{harvnb|Thomasson|2022|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=11–12}} | {{harvnb|Wardy|1998|loc=Lead Section}} }}</ref> Proposed categories include substance, [[Property (philosophy)|property]], [[Relation (philosophy)|relation]], [[State of affairs (philosophy)|state of affairs]], and [[Event (philosophy)|event]].<ref>{{multiref | {{harvnb|Campbell|2006|pp=23–25}} | {{harvnb|Hoffman|Rosenkrantz|2008|p=[https://books.google.com/books?id=Ngdi0a5o5iYC&pg=PA26 26]}} }}</ref> They can be used to provide systems of categories, which offer a comprehensive inventory of reality in which every entity belongs to exactly one category.<ref name="Thomasson2022"/> Some philosophers, like [[Aristotle]], say that entities belonging to different categories exist in distinct ways. Others, like [[John Duns Scotus]], insist that there are no differences in the mode of being, meaning that [[Univocity of being|everything exists in the same way]].<ref>{{multiref | {{harvnb|Widder|2009|pp=[https://books.google.com/books?id=tvWqBgAAQBAJ&pg=PA32 32–35]}} | {{harvnb|LaZella|2019|p=[https://books.google.com/books?id=NCqODwAAQBAJ&pg=PA17 17]}} }}</ref> A related dispute is whether some entities have a higher degree of being than others, an idea already found in [[Plato]]'s work. The more common view in contemporary philosophy is that a thing either exists or not with no intermediary states or degrees.<ref>{{multiref | {{harvnb|Daly|2009|pp=[https://books.google.com/books?id=Bt99AgAAQBAJ&pg=PA227 227–228]}} | {{harvnb|Van Inwagen|2023}} | {{harvnb|Casati|Fujikawa|loc=§3. How Many Ways of Being Existent?}} | {{harvnb|Gibson|1998|pp=5–8}} }}</ref>

The relation between being and non-being is a frequent topic in ontology. Influential issues include the status of [[nonexistent objects]]<ref>{{multiref | {{harvnb|Reicher|2022|loc=[https://plato.stanford.edu/entries/nonexistent-objects/ lead section, §1. The Concept of a Nonexistent Object]}} | {{harvnb|Gibson|1998|p=8}} | {{harvnb|Yao|2014|p=[https://books.google.com/books?id=NZjOAwAAQBAJ&pg=PA140 140]}} }}</ref> and [[Why is there anything at all?|why there is something rather than nothing]].<ref>{{multiref | {{harvnb|Lowe|2005b|p=277}} | {{harvnb|Casati|Fujikawa|loc=Lead Section, §4. Why Is There Something Rather Than Nothing?}} | {{harvnb|Sorensen|2023|loc=Lead Section, §1. Why Is There Something Rather Than Nothing?}} | {{harvnb|Pruss|Rasmussen|2018|pp=4–5}}}}</ref>

=== Particulars and universals ===
{{main|Particular|Universal (metaphysics)|l1=Particulars|l2=Universals}}

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|footer            = The [[Taj Mahal]] is a particular entity while the color ''green'' is a universal entity.
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A central distinction in ontology is between particular and universal entities. Particulars, also called ''individuals'', are unique, non-repeatable entities, like [[Socrates]], the [[Taj Mahal]], and [[Mars]].<ref>{{multiref | {{harvnb|Lowe|2005|p=683}} | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 1a. The Nature of Universals}} | {{harvnb|Bigelow|1998|loc=Lead Section}} | {{harvnb|Campbell|2006|loc=§ Particularity and Individuality}} | {{harvnb|Maurin|2019|loc=Lead Section}} }}</ref> Universals are general, repeatable entities, like the color ''green'', the form ''circularity'', and the virtue ''courage''. Universals express aspects or features shared by particulars. For example, [[Mount Everest]] and [[Mount Fuji]] are particulars characterized by the universal ''mountain''.<ref>{{multiref | {{harvnb|MacLeod|Rubenstein|loc=Lead Section}} | {{harvnb|Bigelow|1998a|loc=Lead Section}} | {{harvnb|Cowling|2019|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=17–19}} }}</ref>

Universals can take the form of properties or relations.<ref>{{multiref | {{harvnb|Campbell|2006|pp=24–25}} | {{harvnb|Bigelow|1998|loc=Lead Section}} }}</ref>{{efn|This idea is opposed by trope theorists, who understand properties and relations as particular entities.<ref>{{harvnb|Campbell|2006|p=25}}</ref>}} Properties describe the characteristics of things. They are features or qualities possessed by an entity.<ref>{{multiref | {{harvnb|Campbell|2006|p=24}} | {{harvnb|Orilia|Paolini Paoletti|2022|loc=Lead Section}} }}</ref> Properties are often divided into [[Property (philosophy)#Essential and accidental|essential and accidental properties]]. A property is essential if an entity must have it; it is accidental if the entity can exist without it.<ref>{{harvnb|Orilia|Paolini Paoletti|2022|loc=§ 1.7 Kinds of Properties}}</ref> For instance, ''having three sides'' is an essential property of a triangle, whereas ''being red'' is an accidental property.<ref>{{harvnb|Vaidya|Wallner|2024|p=[https://books.google.com/books?id=W34IEQAAQBAJ&pg=PA473 473]}}</ref>{{efn|Other influential distinctions are between intrinsic and extrinsic properties, between determinate or determinable properties, and between categorical and dispositional properties.<ref>{{multiref | {{harvnb|Orilia|Paolini Paoletti|2022|loc=§ 1.7 Kinds of Properties, § 5.2. Essentially Categorical vs. Essentially Dispositional Properties}} | {{harvnb|Marshall|Weatherson|2023|loc=Lead Section}} }}</ref>}} Relations are ways how two or more entities stand to one another. Unlike properties, they apply to several entities and characterize them as a group.<ref>{{multiref | {{harvnb|Sider|2010|p=[https://books.google.com/books?id=-KkPEAAAQBAJ&pg=PA13 13]}} | {{harvnb|Bogen|2005|p=798}} | {{harvnb|MacBride|2020|loc=lead section}} | {{harvnb|Campbell|2006|p=25}} }}</ref> For example, ''being a city'' is a property while ''being east of'' is a relation, as in "[[Kathmandu]] is a city" and "Kathmandu is east of [[New Delhi]]".<ref>{{harvnb|MacBride|2020|loc=§ 2. Eliminativism, External Relations and Bradley’s Regress}}</ref> Relations are often divided into [[Relation (philosophy)#Internal and external|internal and external relations]]. Internal relations depend only on the properties of the objects they connect, like the relation of [[Similarity (philosophy)|resemblance]]. External relations express characteristics that go beyond what the connected objects are like, such as spatial relations.<ref>{{multiref | {{harvnb|MacBride|2020|loc=§1. Preliminary Distinctions}} | {{harvnb|Heil|2009|p=316}} | {{harvnb|Armstrong|2010|pp=24–25}} }}</ref>

Substances{{efn|The term ''substance'' has a specific meaning in philosophy distinct from ordinary language expressions such as ''chemical substance'' or ''substance abuse''.<ref>{{harvnb|O'Conaill|2022|p=1}}</ref>}} play an important role in the history of ontology as the particular entities that underlie and support properties and relations. They are often considered the fundamental building blocks of reality that can exist on their own, while entities like properties and relations cannot exist without substances. Substances persist through changes as they acquire or lose properties. For example, when a tomato ripens, it loses the property ''green'' and acquires the property ''red''.<ref>{{multiref | {{harvnb|Campbell|2006|pp=23–24}} | {{harvnb|O'Conaill|2022|pp=1–2, 12–13, 29}} | {{harvnb|Robinson|Weir|2024|loc=Lead Section}} }}</ref>

States of affairs are complex particular entities that have several other entities as their components. The state of affairs "Socrates is wise" has two components: the individual ''Socrates'' and the property ''wise''. States of affairs that correspond to reality are called ''[[fact]]s''.<ref>{{multiref | {{harvnb|Campbell|2006|p=25}} | {{harvnb|Textor|2021|loc=Lead Section}} }}</ref>{{efn|David Armstrong and his followers use a different terminology that does not distinguish between states of affairs and facts.<ref>{{harvnb|Textor|2021|loc=Lead Section}}</ref>}} Facts are [[Truthmaker theory|truthmakers]] of statements, meaning that whether a statement is true or false depends on the underlying facts.<ref>{{harvnb|Textor|2021|loc=Lead Section}}</ref>

Events are particular entities{{efn|Some ontologists also use the term in a less common sense to refer to universals in the form of event types.<ref>{{harvnb|Mackie|2005|p=272}}</ref>}} that occur in time, like the [[fall of the Berlin Wall]] and the [[first moon landing]]. They usually involve some kind of change, like the lawn becoming dry. In some cases, no change occurs, like the lawn staying wet.<ref>{{multiref | {{harvnb|Mackie|2005|p=272}} | {{harvnb|Campbell|2006|p=25}} }}</ref> Complex events, also called ''processes'', are composed of a sequence of events.<ref>{{harvnb|Campbell|2006|p=25}}</ref>

=== Concrete and abstract objects ===
{{Main|Abstract and concrete|l1=Concrete and abstract}}
Concrete objects are entities that exist in space and time, such as a tree, a car, and a planet. They have causal powers and can affect each other, like when a car hits a tree and both are deformed in the process. Abstract objects, by contrast, are outside space and time, such as the number 7 and the set of [[integer]]s. They lack causal powers and do not undergo changes.<ref>{{multiref | {{harvnb|Mackie|1998|loc=Lead Section}} | {{harvnb|Falguera|Martínez-Vidal|Rosen|2022|loc=[https://plato.stanford.edu/entries/abstract-objects/ lead section, § 1. Introduction]}} | {{harvnb|Faye|2013|pp=[https://books.google.com/books?id=ftrmBQAAQBAJ&pg=PA89 89–91]}} | {{harvnb|Prior|2006|pp=498–499}} | {{harvnb|Oliver|2005|p=3}} }}</ref>{{efn|The precise definition is disputed.<ref>{{harvnb|Oliver|2005|p=3}}</ref>}} The existence and nature of abstract objects remain subjects of philosophical debate.<ref>{{multiref | {{harvnb|Oliver|2005|p=3}} | {{harvnb|Plebani|2013|p=[https://books.google.com/books?id=pkNb_3NYyz0C&pg=PA5 5]}} }}</ref>

Concrete objects encountered in everyday life are complex entities composed of various parts. For example, a book is made up of two covers and the pages between them. Each of these components is itself constituted of smaller parts, like [[molecule]]s, [[atom]]s, and [[elementary particle]]s.<ref>{{multiref | {{harvnb|Cornell|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=250–251}} | {{harvnb|Varzi|2019|loc=Lead Section, § 1. 'Part' and Parthood}} | {{harvnb|Cornell|loc=Lead Section, § 2. The Special Composition Question}} | {{harvnb|Tallant|2017|pp=19–21}} }}</ref> [[Mereology]] studies the relation between parts and wholes. One position in mereology says that every collection of entities forms a whole. According to another view, this is only the case for collections that fulfill certain requirements, for instance, that the entities in the collection touch one another.<ref>{{multiref |  {{harvnb|Loux|Crisp|2017|pp=82–83}} | {{harvnb|Cornell|loc=Lead Section, § 2. The Special Composition Question}} | {{harvnb|Brenner|2015|p=1295}} | {{harvnb|Tallant|2017|pp=19–21, 23–24, 32–33}} | {{harvnb|Cornell|loc=Lead Section}}}}</ref> The problem of material constitution asks whether or in what sense a whole should be considered a new object in addition to the collection of parts composing it.<ref>{{multiref | {{harvnb|Rea|1997|pp=[https://books.google.com/books?id=a0QOWVtDOXYC&pg=PR15 xv–xvi]}} | {{harvnb|Korman|2021|loc=Lead Section}} }}</ref>

Abstract objects are closely related to fictional and [[Object of the mind|intentional objects]]. Fictional objects are entities invented in works of [[fiction]]. They can be things, like the [[One Ring]] in [[J. R. R. Tolkien]]'s book series [[The Lord of the Rings]], and people, like the [[Monkey King]] in the novel [[Journey to the West]].<ref>{{multiref | {{harvnb|Kroon|Voltolini|2023|loc=Lead Section}} | {{harvnb|Lamarque|1998|loc=Lead Section}} | {{harvnb|Prior|2006|p=493}} }}</ref> Some philosophers say that fictional objects are abstract objects and exist outside space and time. Others understand them as artifacts that are created as the works of fiction are written.<ref>{{multiref | {{harvnb|Kroon|Voltolini|2023|loc=§ 1. The Metaphysics of Fictional Entities}} | {{harvnb|Lamarque|1998|loc=§ 3. Hospitable theories}} }}</ref> Intentional objects are entities that exist within [[mental states]], like [[perception]]s, [[belief]]s, and [[desire]]s. For example, if a person thinks about the [[Loch Ness Monster]] then the Loch Ness Monster is the intentional object of this [[thought]]. People can think about existing and non-existing objects. This makes it difficult to assess the [[Intentionality#The problem of intentional inexistence|ontological status of intentional objects]].<ref>{{multiref | {{harvnb|Jacob|2023|loc=2. Intentional inexistence}} | {{harvnb|Kriegel|2007|pp=307–308}} | {{harvnb|O’Madagain|loc=§ 2. Intentional Objects}} }}</ref>

=== Other concepts ===
Ontological dependence is a relation between entities. An entity depends ontologically on another entity if the first entity cannot exist without the second entity.<ref>{{multiref | {{harvnb|Ney|2014|pp=53–55}} | {{harvnb|Fine|1995|pp=269–270}} }}</ref> For instance, the surface of an apple cannot exist without the apple.<ref>{{harvnb|Nuñez Erices|2019|pp=15–16}}</ref> An entity is ontologically independent if it does not depend on anything else, meaning that it is fundamental and can exist on its own. Ontological dependence plays a central role in ontology and its attempt to describe reality on its most fundamental level.<ref>{{multiref | {{harvnb|Ney|2014|pp=53–55}} | {{harvnb|Fine|1995|pp=269–270}} }}</ref> It is closely related to [[Grounding (metaphysics)|metaphysical grounding]], which is the relation between a ground and the facts it explains.<ref>{{multiref | {{harvnb|Tahko|Lowe|2020|loc=§ 5. Ontological Dependence and Metaphysical Grounding}} | {{harvnb|Ney|2014|pp=53–55}} }}</ref>

[[File:Willard Van Orman Quine on Bluenose II in Halifax NS harbor 1980.jpg|thumb|upright=.8|alt=Photo of Willard Van Orman Quine|[[Willard Van Orman Quine]] used the concept of [[ontological commitment]]s to analyze theories.]]

An [[ontological commitment]] of a person or a theory is an entity that exists according to them.<ref>{{multiref | {{harvnb|Ney|2014|p=31}} | {{harvnb|Jubien|1998|loc=Lead Section}} }}</ref> For instance, a person who [[Theism|believes in God]] has an ontological commitment to [[God]].<ref>{{harvnb|Jubien|1998|loc=Lead Section}}</ref> Ontological commitments can be used to analyze which ontologies people explicitly defend or implicitly assume. They play a central role in contemporary metaphysics when trying to decide between competing theories. For example, the [[Quine–Putnam indispensability argument]] defends [[mathematical Platonism]], asserting that numbers exist because the best scientific theories are ontologically committed to numbers.<ref>{{multiref | {{harvnb|Colyvan|2001|p=23}} | {{harvnb|Bangu|2012|pp=26–27}} | {{harvnb|Ney|2014|pp=40–43}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} }}</ref>

Possibility and necessity are further topics in ontology. Possibility describes what can be the case, as in "it is possible that [[extraterrestrial life]] exists". Necessity describes what must be the case, as in "it is necessary that three plus two equals five". Possibility and necessity contrast with actuality, which describes what is the case, as in "[[Doha]] is the capital of [[Qatar]]". Ontologists often use the concept of [[possible world]]s to analyze possibility and necessity.<ref>{{multiref | {{harvnb|Parent|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=149–150}} | {{harvnb|Koons|Pickavance|2015|pp=154–155}} | {{harvnb|Mumford|2012|loc=§ 8. What Is Possible?}} }}</ref> A possible world is a complete and consistent way how things could have been.<ref>{{multiref | {{harvnb|Berto|Jago|2023|loc=Lead Section}} | {{harvnb|Pavel|1986|p=[https://books.google.com/books?id=OF7ZA54UpYYC&pg=PA50 50]}} }}</ref> For example, [[Haruki Murakami]] was born in 1949 in the actual world but there are possible worlds in which he was born at a different date. Using this idea, [[possible world semantics]] says that a sentence is possibly true if it is true in at least one possible world. A sentence is necessarily true if it is true in all possible worlds.<ref>{{multiref | {{harvnb|Menzel|2023|loc=Lead Section, § 1. Possible Worlds and Modal Logic}} | {{harvnb|Kuhn|2010|p=[https://books.google.com/books?id=c_eYe6NVaDMC&pg=PA13 13]}} }}</ref>

In ontology, [[Identity (philosophy)|identity]] means that two things are the same. Philosophers distinguish between qualitative and numerical identity. Two entities are qualitatively identical if they have exactly the same features, such as perfect identical twins. This is also called ''exact similarity'' and ''indiscernibility''. Numerical identity, by contrast, means that there is only a single entity. For example, if Fatima is the mother of Leila and Hugo then Leila's mother is numerically identical to Hugo's mother.<ref>{{multiref | {{harvnb|Kirwan|2005|pp=417–418}} | {{harvnb|Noonan|Curtis|2022|loc=Lead Section}} | {{harvnb|Kuhlmann|2010|pp=1867–1867b}} }}</ref> Another distinction is between synchronic and diachronic identity. Synchronic identity relates an entity to itself at the same time. Diachronic identity relates an entity to itself at different times, as in "the woman who bore Leila three years ago is the same woman who bore Hugo this year".<ref>{{multiref | {{harvnb|Gallois|2016|loc=§ 2.1 Diachronic and Synchronic Identity}} | {{harvnb|Noonan|Curtis|2022|loc=Lead Section, § 5. Identity Over Time}} }}</ref>

== Branches ==
There are different and sometimes overlapping ways to divide ontology into branches. Pure ontology focuses on the most abstract topics associated with the concept and nature of being. It is not restricted to a specific domain of entities and studies existence and the structure of reality as a whole.<ref>{{multiref | {{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PR11 xi–xii]}} | {{harvnb|Sadegh-Zadeh|2011|p=[https://books.google.com/books?id=YenvCAAAQBAJ&pg=PA384 384]}} }}</ref> Pure ontology contrasts with [[applied ontology]], also called domain ontology. Applied ontology examines the application of ontological theories and principles to specific disciplines and domains, often in the field of science.<ref>{{multiref | {{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PR11 xi–xii]}} | {{harvnb|Smith|Klagges|2008|p=21}} | {{harvnb|Sadegh-Zadeh|2011|p=[https://books.google.com/books?id=YenvCAAAQBAJ&pg=PA384 384]}} }}</ref> It considers ontological problems in regard to specific entities such as [[matter]], [[mind]], [[number]]s, [[God]], and cultural artifacts.<ref>{{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PR12 xii–xiii]}}</ref>

[[Social ontology]], a major subfield of applied ontology, studies social kinds, like [[money]], [[gender]], [[society]], and [[language]]. It aims to determine the nature and essential features of these concepts while also examining their mode of existence.<ref>{{multiref | {{harvnb|Epstein|2024|loc=Lead Section}} | {{harvnb|Tuomela|Hakli|Mäkelä|2020|loc=[https://books.google.com/books?id=P23cDwAAQBAJ&pg=PT9 § 1. Background to Social Ontology]}} }}</ref> According to a common view, social kinds are useful constructions to describe the complexities of social life. This means that they are not pure fictions but, at the same time, lack the objective or mind-independent reality of natural phenomena like elementary particles, lions, and stars.<ref>{{multiref|{{harvnb|Ney|2014|pp=259–263}}|{{harvnb|Rea|2021|pp=185–186}}}}</ref> In the fields of [[computer science]], [[information science]], and [[knowledge representation]], applied ontology is interested in the development of formal frameworks to encode and store information about a limited domain of entities in a structured way.<ref>{{multiref | {{harvnb|Smith|Klagges|2008|p=21}} | {{harvnb|Hawley|2016|pp=168–170}} }}</ref> A related application in [[genetics]] is [[Gene Ontology]], which is a comprehensive framework for the standardized representation of gene-related information across species and databases.<ref>{{multiref | {{harvnb|Smith|Klagges|2008|pp=35–36}} | {{harvnb|Haritha|Priyatharshini|Abishek|Kiran|2018|p=[https://books.google.com/books?id=LcpmDwAAQBAJ&pg=PA489 489]}} }}</ref>

[[Formal ontology]] is the study of objects in general while focusing on their abstract structures and features. It divides objects into different categories based on the forms they exemplify. Formal ontologists often rely on the tools of [[formal logic]] to express their findings in an abstract and general manner.<ref>{{multiref | {{harvnb|Hennig|2008|pp=43–44}} | {{harvnb|Hakkarainen|Keinänen|2023|pp=[https://books.google.com/books?id=1oHZEAAAQBAJ&pg=PA1 1–2]}} | {{harvnb|Albertazzi|1996|p=199}} }}</ref>{{efn|The idea of formal ontology was first formulated by phenomenologist [[Edmund Husserl]], who studied objects in general by relying on fundamental categories such as unity, plurality, state of affairs, part, and whole. He examined the relations between these categories and how they depend on one another.<ref>{{multiref | {{harvnb|Albertazzi|1996|pp=199, 206}} | {{harvnb|Hennig|2008|pp=43–44}} }}</ref>}} Formal ontology contrasts with material ontology, which distinguishes between different areas of objects and examines the features characteristic of a specific area.<ref>{{multiref | {{harvnb|Albertazzi|1996|pp=199–200}} | {{harvnb|Poli|Simons|1996|pp=vii–viii}} | {{harvnb|Hakkarainen|Keinänen|2023|p=[https://books.google.com/books?id=1oHZEAAAQBAJ&pg=PA9 9]}} }}</ref> Examples are ideal spatial beings in the area of geometry and living beings in the area of biology.<ref>{{harvnb|Hakkarainen|Keinänen|2023|p=[https://books.google.com/books?id=1oHZEAAAQBAJ&pg=PA9 9]}}</ref>

Descriptive ontology aims to articulate the conceptual scheme underlying how people ordinarily think about the world. Prescriptive ontology departs from common conceptions of the structure of reality and seeks to formulate a new and better conceptualization.<ref>{{multiref | {{harvnb|Berto|Plebani|2015|pp=35–36}} | {{harvnb|Phillips|1967|pp=105–106}} | {{harvnb|Haack|1979|pp=361–362}} }}</ref>

Another contrast is between analytic and speculative ontology. Analytic ontology examines the types and categories of being to determine what kinds of things could exist and what features they would have. Speculative ontology aims to determine which entities actually exist, for example, whether there are numbers or whether time is an illusion.<ref>{{multiref | {{harvnb|Coggins|2010|p=[https://books.google.com/books?id=tBh_DAAAQBAJ&pg=PA93 93]}} | {{harvnb|Lehrer|1993|p=[https://books.google.com/books?id=w590r7cZ8TsC&pg=PR11 xi]}} }}</ref>

[[File:Heidegger 3 (1960).jpg|thumb|upright=.8|[[Martin Heidegger]] proposed fundamental ontology to study the meaning of being.]]

[[Metaontology]] studies the underlying concepts, assumptions, and methods of ontology. Unlike other forms of ontology, it does not ask "what exists" but "what does it mean for something to exist" and "how can people determine what exists".<ref>{{multiref | {{harvnb|Berto|Plebani|2015|p=2}} | {{harvnb|Göhner|Steinbrink|2018|pp=[https://books.google.com/books?id=FuBLDwAAQBAJ&pg=PA42 42, 52–53]}} }}</ref> It is closely related to [[fundamental ontology]], an approach developed by philosopher [[Martin Heidegger]] that seeks to uncover the meaning of being.<ref>{{multiref | {{harvnb|Wheeler|2020|loc=§ 2.2.1 The Question}} | {{harvnb|Schalow|2019|p=[https://books.google.com/books?id=nJ27DwAAQBAJ&pg=PA139 139]}} }}</ref>

== Schools of thought ==
=== Realism and anti-realism ===
{{main|Philosophical realism|Anti-realism}}
The term ''realism'' is used for various theories{{efn|They are usually distinguished by combining them with a qualifier to express which type is meant, as in  ''ontological realism'', ''mathematical realism'', and ''moral realism''. The qualifiers are sometimes left out if the meaning is clear in the context.<ref>{{harvnb|Niiniluoto|2002|pp=1–2, 21, 25–26, 28–29}}</ref>}} that affirm that some kind of phenomenon is real or has mind-independent existence. Ontological realism is the view that there are [[Subjectivity and objectivity (philosophy)|objective]] facts about what exists and what the nature and categories of being are. Ontological realists do not make claims about what those facts are, for example, whether elementary particles exist. They merely state that there are mind-independent facts that determine which ontological theories are true.<ref>{{multiref | {{harvnb|Niiniluoto|2002|pp=1–2, 21, 25–26}} | {{harvnb|Chalmers|2009|pp=77–78}} | {{harvnb|Sider|2009|pp=385–386}} }}</ref> This idea is denied by ontological anti-realists, also called ontological deflationists, who say that there are no substantive facts one way or the other.<ref>{{multiref | {{harvnb|Chalmers|2009|pp=77–78}} | {{harvnb|Sider|2009|pp=385–386}} }}</ref> According to philosopher [[Rudolf Carnap]], for example, ontological statements are relative to language and depend on the ontological framework of the speaker. This means that there are no framework-independent ontological facts since different frameworks provide different views while there is no objectively right or wrong framework.<ref>{{multiref | {{harvnb|Chalmers|2009|p=78}} | {{harvnb|Hofweber|2023|loc=§ 4.4 Carnap’s rejection of ontology. (L1) meets (O4) and (the end of?) (O2)}} }}</ref>

[[File:Sanzio 01 Plato Aristotle.jpg|thumb|alt=Fresco showing Plato and Aristotle|[[Plato]] (left) and [[Aristotle]] (right) disagreed on whether universals can exist without matter.]]

In a more narrow sense, realism refers to the existence of certain types of entities.<ref>{{harvnb|Niiniluoto|2002|pp=1–2, 21, 25–26, 28–29}}</ref> Realists about universals say that universals have mind-independent existence. According to [[Theory of forms|Platonic realists]], universals exist not only independent of the mind but also independent of particular objects that exemplify them. This means that the universal ''red'' could exist by itself even if there were no red objects in the world. Aristotelian realism, also called [[moderate realism]], rejects this idea and says that universals only exist as long as there are objects that exemplify them. [[Conceptualism]], by contrast, is a form of anti-realism, stating that universals only exist in the mind as concepts that people use to understand and categorize the world. [[Nominalism|Nominalists]] defend a strong form of anti-realism by saying that universals have no existence. This means that the world is entirely composed of particular objects.<ref>{{multiref | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 2. Versions of Realism, § 3. Versions of Anti-Realism}} | {{harvnb|Bigelow|1998a|loc=§ 4. Nominalism and Realism}} | {{harvnb|Loux|Crisp|2017|pp=17–19, 45}} | {{harvnb|Niiniluoto|2002|pp=28–29}}}}</ref>

[[Mathematical realism]], a closely related view in the [[philosophy of mathematics]], says that mathematical facts exist independently of human language, thought, and practices and are discovered rather than invented. According to mathematical Platonism, this is the case because of the existence of [[mathematical objects]], like numbers and sets. Mathematical Platonists say that mathematical objects are as real as physical objects, like atoms and stars, even though they are not accessible to [[empirical observation]].<ref>{{multiref | {{harvnb|Blanchette|1998|loc=Lead Section}} | {{harvnb|Moore|1998|loc=Lead Section}} | {{harvnb|Balaguer|2009|p=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PA36 36]}} | {{harvnb|Linnebo|2024|loc=Lead Section}} }}</ref> Influential forms of mathematical anti-realism include conventionalism, which says that mathematical theories are trivially true simply by how mathematical terms are defined, and game [[Formalism (philosophy of mathematics)|formalism]], which understands mathematics not as a theory of reality but as a game governed by rules of string manipulation.<ref>{{multiref | {{harvnb|Balaguer|2009|pp=[https://books.google.com/books?id=mbn35b2ghgkC&pg=PA36 36, 44]}} | {{harvnb|Weir|2024|loc=Lead Section}} }}</ref>

[[Modal realism]] is the theory that in addition to the actual world, there are countless [[possible world]]s as real and concrete as the actual world. The primary difference is that the actual world is inhabited by us while other possible worlds are inhabited by our [[Counterpart theory|counterparts]]. Modal anti-realists reject this view and argue that possible worlds do not have concrete reality but exist in a different sense, for example, as abstract or fictional objects.<ref>{{multiref | {{harvnb|Borghini|2016|pp=[https://books.google.com/books?id=Ifw8CwAAQBAJ&pg=PA91 91–93]}} | {{harvnb|Chihara|2001|pp=[https://doi.org/10.1093/acprof:oso/9780199246557.003.0005 142–143]}} | {{harvnb|Parent|loc=Lead section}} }}</ref>

[[Scientific realism|Scientific realists]] say that the scientific description of the world is an accurate representation of reality.{{efn|The exact definition of the term is disputed.<ref>{{harvnb|Chakravartty|2017|loc=§ 1. What is Scientific Realism?}}</ref>}} It is of particular relevance in regard to things that [[Unobservable|cannot be directly observed]] by humans but are assumed to exist by scientific theories, like electrons, forces, and laws of nature. [[Scientific anti-realism]] says that scientific theories are not descriptions of reality but [[Instrumentalism|instruments]] to predict observations and the outcomes of experiments.<ref>{{multiref | {{harvnb|Chakravartty|2017|loc=Lead Section, § 1. What is Scientific Realism?}} | {{harvnb|Liston|loc=Lead Section, § 6b. The Observable-Unobservable Distinction}} | {{harvnb|Okasha|2016|pp=[https://books.google.com/books?id=GMqSDAAAQBAJ&pg=PA54 54–55]}} }}</ref>

[[Moral realism|Moral realists]] claim that there exist mind-independent moral facts. According to them, there are objective principles that determine which behavior is morally right. [[Moral anti-realism|Moral anti-realists]] either claim that moral principles are subjective and differ between persons and cultures, a position known as [[moral relativism]], or outright deny the existence of moral facts, a view referred to as [[moral nihilism]].<ref>{{multiref | {{harvnb|DeLapp|loc=Lead Section, § 4a. Moral Realisms, § 4b. Moral Relativisms}} | {{harvnb|Sayre-McCord|2023a|loc=Lead Section}} | {{harvnb|Gowans|2021|loc=Lead Section, § 2. Forms and Arguments}} | {{harvnb|Westacott|loc=Lead Section}} | {{harvnb|Dreier|2007|pp=240–241}} }}</ref>

=== By number of categories ===
Monocategorical theories say that there is only one fundamental category, meaning that every single entity belongs to the same universal class.<ref>{{multiref | {{harvnb|Van Inwagen|2011|pp=389–390}} | {{harvnb|Paul|2017|pp=32–33}} | {{harvnb|Woznicki|2022|p=97}} }}</ref> For example, some forms of nominalism state that only concrete particulars exist while some forms of [[bundle theory]] state that only properties exist.<ref>{{harvnb|Van Inwagen|2011|pp=389–390}}</ref> Polycategorical theories, by contrast, hold that there is more than one basic category, meaning that entities are divided into two or more fundamental classes. They take the form of systems of categories, which list the highest genera of being to provide a comprehensive inventory of everything.<ref>{{multiref | {{harvnb|Van Inwagen|2011|pp=389–390}} | {{harvnb|Paul|2017|pp=32–33}} | {{harvnb|Woznicki|2022|p=97}} }}</ref>

The closely related discussion between [[monism]] and [[Mind–body dualism|dualism]] is about the most fundamental types that make up reality. According to monism, there is only one kind of thing or substance on the most basic level.<ref>{{multiref | {{harvnb|Schaffer|2018|loc=Lead Section}} | {{harvnb|Robinson|2023|loc=§ Lead Section}} }}</ref> [[Materialism]] is an influential monist view; it says that everything is material. This means that mental phenomena, such as beliefs, emotions, and consciousness, either do not exist or exist as aspects of matter, like brain states. [[Idealists]] take the converse perspective, arguing that everything is mental. They may understand physical phenomena, like rocks, trees, and planets, as ideas or perceptions of conscious minds.<ref>{{multiref | {{harvnb|McLaughlin|1999|pp=685–691}} | {{harvnb|Kim|2005|p=608}} | {{harvnb|Sprigge|1998|loc=Lead Section}} }}</ref> [[Neutral monism]] occupies a middle ground by saying that both mind and matter are derivative phenomena.<ref>{{multiref | {{harvnb|Stubenberg|Wishon|2023|loc=Lead Section; § 1.3 Mind and Matter Revisited}} | {{harvnb|Griffin|1998}} }}</ref> Dualists state that mind and matter exist as independent principles, either as [[Substance dualism|distinct substances]] or [[Property dualism|different types of properties]].<ref>{{multiref | {{harvnb|Calef|loc=Lead Section}} | {{harvnb|Robinson|2023|loc=§ Lead Section}} }}</ref> In a slightly different sense, monism contrasts with [[Pluralism (philosophy)|pluralism]] as a view not about the number of basic types but the number of entities. In this sense, monism is the controversial position that only a single all-encompassing entity exists in all of reality.{{efn|According to some [[Pantheism|pantheists]], this entity is God.<ref>{{harvnb|Levine|2002|pp=[https://books.google.com/books?id=GAYyLrfsZvUC 71–72, 84–85]}}</ref>}} Pluralism is more commonly accepted and says that several distinct entities exist.<ref>{{harvnb|Schaffer|2018|loc=Lead Section}}</ref>

=== By fundamental categories ===
The historically influential [[Substance theory|substance-attribute ontology]] is a polycategorical theory. It says that reality is at its most fundamental level made up of unanalyzable substances that are characterized by universals, such as the properties an individual substance has or relations that exist between substances.<ref>{{multiref | {{harvnb|Paul|2017|p=34}} | {{harvnb|Robinson|Weir|2024|loc=§ Lead section}} | {{harvnb|O'Conaill|2022|pp=1–3}} }}</ref> The closely related to substratum theory says that each concrete object is made up of properties and a substratum. The difference is that the substratum is not characterized by properties: it is a featureless or ''bare particular'' that merely supports the properties.<ref>{{multiref | {{harvnb|Paul|2017|pp=34–35}} | {{harvnb|Robinson|Weir|2024|loc=§ 3.2.2. The concept of substratum or 'thin particular'}} }}</ref>

Various alternative ontological theories have been proposed that deny the role of substances as the foundational building blocks of reality.<ref>{{multiref | {{harvnb|O'Conaill|2022|pp=52–53}} | {{harvnb|Robinson|Weir|2024|loc=§ Lead section}} }}</ref> Stuff ontologies say that the world is not populated by distinct entities but by continuous stuff that fills space. This stuff may take various forms and is often conceived as infinitely divisible.<ref>{{multiref | {{harvnb|O'Conaill|2022|p=53}} | {{harvnb|Esfeld|2020|pp=[https://books.google.com/books?id=OJgIEQAAQBAJ&pg=PA464 464–465]}} }}</ref>{{efn|This view contrasts with atomism, which states that the world is composed of discrete, indivisible units.<ref>{{harvnb|Esfeld|2020|pp=[https://books.google.com/books?id=OJgIEQAAQBAJ&pg=PA459 459–460]}}</ref>}} According to [[Process philosophy|process ontology]], processes or events are the fundamental entities. This view usually emphasizes that nothing in reality is static, meaning that being is dynamic and characterized by constant change.<ref>{{multiref | {{harvnb|O'Conaill|2022|p=53}} | {{harvnb|Robinson|Weir|2024|loc=§ Lead section}} | {{harvnb|Rescher|2000|pp=[https://books.google.com/books?id=E6rOyLVeBOcC&pg=PA5 5–6]}} }}</ref> Bundle theories state that there are no regular objects but only bundles of co-present properties. For example, a lemon may be understood as a bundle that includes the properties yellow, sour, and round. According to traditional bundle theory, the bundled properties are universals, meaning that the same property may belong to several different bundles. According to [[Trope_(philosophy)#In_metaphysics|trope]] bundle theory, properties are particular entities that belong to a single bundle.<ref>{{multiref | {{harvnb|Paul|2017|pp=35–37}} | {{harvnb|O'Conaill|2022|pp=52–53}} }}</ref>

Some ontologies focus not on distinct objects but on interrelatedness. According to relationalism, all of reality is relational at its most fundamental level.<ref>{{multiref | {{harvnb|Heil|2009|p=310}} | {{harvnb|Runggaldier|2009|p=[https://books.google.com/books?id=opLRzEaauTUC&pg=PA248 248]}} | {{harvnb|Lupisella|2020|p=[https://books.google.com/books?id=3JTyDwAAQBAJ&pg=PA70 70]}} }}</ref>{{efn|For example, [[Relationalism#Relationalism (theory of space and time)|relationalism about spacetime]] says that space and time are nothing but relations. Spacetime substantivalists reject this view and state that spacetime is a distinct object rather than a relational structure between objects.<ref>{{multiref | {{harvnb|Hoefer|Huggett|Read|2023|loc=Lead Section}} | {{harvnb|Benovsky|2016|pp=[https://books.google.com/books?id=4KHWCwAAQBAJ&pg=PA19 19–20]}} | {{harvnb|Romero|2018|p=[https://books.google.com/books?id=5wJ2DwAAQBAJ&pg=PA135 135]}} }}</ref>}} [[Ontic structural realism]] agrees with this basic idea and focuses on how these relations form complex structures. Some structural realists state that there is nothing but relations, meaning that individual objects do not exist. Others say that individual objects exist but depend on the structures in which they participate.<ref>{{multiref | {{harvnb|Esfeld|2020|pp=[https://books.google.com/books?id=OJgIEQAAQBAJ&pg=PA461 461–462]}} | {{harvnb|Ladyman|2023|loc=§ 4. Ontic Structural Realism (OSR)}} }}</ref> Fact ontologies present a different approach by focusing on how entities belonging to different categories come together to constitute the world. Facts, also known as states of affairs, are complex entities; for example, the fact that ''the Earth is a planet'' consists of the particular object ''the Earth'' and the property ''being a planet''. Fact ontologies state that facts are the fundamental constituents of reality, meaning that objects, properties, and relations cannot exist on their own and only form part of reality to the extent that they participate in facts.<ref>{{multiref | {{harvnb|Campbell|2006|p=25 |loc=§ States of affairs}} | {{harvnb|Rosenkrantz|2018|pp=1–4}} | {{harvnb|Armstrong|2010|pp=[https://books.google.com/books?id=pbGI46EoQKEC&pg=PA26 26–28]}} }}</ref>{{efn|This is expressed in a slogan by [[Ludwig Wittgenstein]]: "The world is the totality of facts, not of things".<ref>{{harvnb|Wittgenstein|2001}}</ref>}}

In the [[history of philosophy]], various ontological theories based on several fundamental categories have been proposed. One of the first theories of categories was suggested by [[Aristotle]], whose system includes ten categories: substance, [[quantity]], [[Quality (philosophy)|quality]], relation, place, date, posture, state, action, and passion.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.1 Aristotelian Realism}} | {{harvnb|Studtmann|2024|loc=§ 2. The Ten-Fold Division}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Aristotle}} }}</ref> An early influential system of categories in Indian philosophy, first proposed in the [[Vaisheshika]] school, distinguishes between six categories: [[dravya|substance]], quality, motion, universal, individuator, and inherence.<ref>{{multiref | {{harvnb|Westerhoff|2019|loc=§ Three important systems of categories: Vaiśeṣika}} | {{harvnb|Kumar|2019|p=[https://books.google.com/books?id=Jr2YDwAAQBAJ&pg=PA34 34]}} }}</ref> [[Immanuel Kant]]'s [[transcendental idealism]] includes a system of twelve categories, which Kant saw as pure concepts of understanding. They are subdivided into four classes: quantity, quality, relation, and modality.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.2 Kantian Conceptualism}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Kant}} }}</ref> In more recent philosophy, theories of categories were developed by [[C. S. Peirce]], [[Edmund Husserl]], [[Samuel Alexander]], [[Roderick Chisholm]], and [[E. J. Lowe (philosopher)|E. J. Lowe]].<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.3 Husserlian Descriptivism, § 1.4 Contemporary Category Systems}} | {{harvnb|Grim|Rescher|2023|p=[https://books.google.com/books?id=KgPPEAAAQBAJ&pg=PT39 39]}} }}</ref>

=== Others ===
The dispute between constituent and relational ontologies{{efn|In this context, the term "relational ontology" has a slightly different meaning than the term "relationalism", which says that, at the most basic level, reality is made up of relations.<ref>{{multiref | {{harvnb|Rea|2021|pp=104–105}} | {{harvnb|Heil|2009|p=310}} | {{harvnb|Runggaldier|2009|p=[https://books.google.com/books?id=opLRzEaauTUC&pg=PA248 248]}} | {{harvnb|Lupisella|2020|p=[https://books.google.com/books?id=3JTyDwAAQBAJ&pg=PA70 70]}} }}</ref>}} concerns the internal structure of concrete particular objects. Constituent ontologies say that objects have an internal structure with properties as their component parts. Bundle theories are an example of this position: they state that objects are bundles of properties. This view is rejected by relational ontologies, which say that objects have no internal structure, meaning that properties do not inhere in them but are externally related to them. According to one analogy, objects are like pin-cushions and properties are pins that can be stuck to objects and removed again without becoming a real part of objects. Relational ontologies are common in certain forms of nominalism that reject the existence of universal properties.<ref>{{multiref | {{harvnb|Rea|2021|pp=104–105}} | {{harvnb|Van Inwagen|2011|pp=390–392}} | {{harvnb|Koslicki|2018|p=[https://books.google.com/books?id=th1rDwAAQBAJ&pg=PA11 11]}} | {{harvnb|Rettler|Bailey|2023|loc=§ 3.2 What Objects Are}} }}</ref>

Hierarchical ontologies state that the world is organized into levels. Entities on all levels are real but low-level entities are more fundamental than high-level entities. This means that they can exist without high-level entities while high-level entities cannot exist without low-level entities.<ref>{{multiref | {{harvnb|Houng|2012|pp=[https://books.google.com/books?id=M6T6CAAAQBAJ&pg=PA106 106–110]}} | {{harvnb|Schaffer|2009|pp=347–348, 354–356}} | {{harvnb|Ceder|2018|loc=§ Flat ontology}} }}</ref> One hierarchical ontology says that elementary particles are more fundamental than the macroscopic objects they compose, like chairs and tables. Other hierarchical theories assert that substances are more fundamental than their properties and that nature is more fundamental than culture.<ref>{{multiref | {{harvnb|Schaffer|2010|pp=31, 44–45}} | {{harvnb|Schaffer|2009|pp=354–356}} | {{harvnb|Ceder|2018|loc=§ Flat ontology}} }}</ref> Flat ontologies, by contrast, deny that any entity has a privileged status, meaning that all entities exist on the same level. For them, the main question is only whether something exists rather than identifying the level at which it exists.<ref>{{multiref | {{harvnb|Houng|2012|pp=[https://books.google.com/books?id=M6T6CAAAQBAJ&pg=PA106 106–110]}} | {{harvnb|Schaffer|2009|pp=347–348, 354–356}} | {{harvnb|Ceder|2018|loc=§ Flat ontology}} }}</ref>{{efn|Some flat ontologies allow that there are entities on higher levels but stipulate that they are reducible to the lowest level, meaning that they are no addition to being.<ref>{{harvnb|Houng|2012|pp=[https://books.google.com/books?id=M6T6CAAAQBAJ&pg=PA106 106–110]}}</ref>}}

The ontological theories of [[endurantism]] and [[perdurantism]] aim to explain how material objects persist through time. Endurantism is the view that material objects are three-dimensional entities that travel through time while being fully present in each moment. They remain the same even when they gain or lose properties as they change. Perdurantism is the view that material objects are four-dimensional entities that extend not just through space but also through time. This means that they are composed of [[temporal part]]s and, at any moment, only one part of them is present but not the others. According to perdurantists, change means that an earlier part exhibits different qualities than a later part. When a tree loses its leaves, for instance, there is an earlier temporal part with leaves and a later temporal part without leaves.<ref>{{multiref | {{harvnb|Miller|2018|loc=Lead Section}} | {{harvnb|Costa|loc=Lead Section, § 1. Theories of Persistence}} | {{harvnb|Simons|2013|p=[https://books.google.com/books?id=ql27m77IveQC&pg=PA166 166]}} | {{harvnb|Hawley|2023|loc=3. Change and Temporal Parts}} }}</ref>

Differential ontology is a [[poststructuralist]] approach interested in the relation between the concepts of identity and [[Difference (philosophy)|difference]]. It says that traditional ontology sees identity as the more basic term by first characterizing things in terms of their essential features and then elaborating differences based on this conception. Differential ontologists, by contrast, privilege difference and say that the identity of a thing is a secondary determination that depends on how this thing differs from other things.<ref>{{multiref | {{harvnb|Cisney|loc=Lead Section}} | {{harvnb|Rae|2020|p=[https://www.cambridge.org/core/books/abs/poststructuralist-agency/deleuze-differential-ontology-and-subjectivity/1C78F8C61B72EBF95B5C687DF75F06E0 33]}} | {{harvnb|Rae|2014|p=86}} }}</ref>

[[Object-oriented ontology]] belongs to the school of [[speculative realism]] and examines the nature and role of objects. It sees objects as the fundamental building blocks of reality. As a flat ontology, it denies that some entities have a more fundamental form of existence than others. It uses this idea to argue that objects exist independently of human thought and perception.<ref>{{multiref | {{harvnb|Young|2021|pp=83–84}} | {{harvnb|Isrow|2022|p=[https://books.google.com/books?id=MrB7EAAAQBAJ&pg=PA28 28]}} | {{harvnb|Neyrat|2020|p=[https://books.google.com/books?id=e_nJDwAAQBAJ&pg=PT13 13]}} }}</ref>

== Methods ==
[[Philosophical methodology|Methods]] of ontology are ways of conducting ontological inquiry and deciding between competing theories. There is no single standard method; the diverse approaches are studied by [[metaontology]].<ref>{{multiref | {{harvnb|Effingham|2013|loc=§ Methodology: Metaontology}} | {{harvnb|Berto|Plebani|2015|p=2}} }}</ref>

[[Conceptual analysis]] is a method to understand ontological concepts and clarify their meaning.<ref>{{harvnb|Thomasson|2012|pp=175–176}}</ref> It proceeds by analyzing their component parts and the [[necessary and sufficient conditions]] under which a concept applies to an entity.<ref>{{multiref | {{harvnb|Garcia-Godinez|2023|pp=[https://books.google.com/books?id=aXjEEAAAQBAJ&pg=PA189 189–192]}} | {{harvnb|Shaffer|2015|pp=[https://www.jstor.org/stable/26602327 555–556]}} }}</ref> This information can help ontologists decide whether a certain type of entity, such as numbers, exists.<ref>{{harvnb|Garcia-Godinez|2023|pp=[https://books.google.com/books?id=aXjEEAAAQBAJ&pg=PA186 186, 188–189]}}</ref> [[Eidetic variation]] is a related method in [[Phenomenology (philosophy)|phenomenological]] ontology that aims to identify the essential features of different types of objects. Phenomenologists start by imagining an example of the investigated type. They proceed by varying the imagined features to determine which ones cannot be changed, meaning they are essential.<ref>{{multiref | {{harvnb|Drummond|2022|p=[https://books.google.com/books?id=VQ9hEAAAQBAJ&pg=PA75 75]}} | {{harvnb|Ryckman|2005|pp=[https://books.google.com/books?id=FI1JCAAAQBAJ&pg=PA142 142–144]}} }}</ref>{{efn|For example, it is essential for a triangle to have three sides since it ceases to be a triangle if a fourth side is added.<ref>{{harvnb|Spear|loc=§ 3. Ideas Pertaining to a Pure Phenomenology and to a Phenomenological Philosophy: The Perceptual Noema}}</ref>}} The [[Transcendental arguments|transcendental]] method begins with a simple observation that a certain entity exists. In the following step, it studies the ontological repercussions of this observation by examining how it is possible or which [[condition of possibility|conditions]] are required for this entity to exist.<ref>{{multiref | {{harvnb|Gabriel|2011|pp=ix-x}} | {{harvnb|Körner|1984|pp=[https://books.google.com/books?id=eAA4AAAAIAAJ&pg=PA183 183–184]}} | {{harvnb|Pihlström|2009|pp=[https://books.google.com/books?id=srGLpb7pWdkC&pg=PA60 60–61]}} }}</ref>

Another approach is based on [[intuition]]s in the form of non-inferential impressions about the correctness of general principles.<ref>{{multiref | {{harvnb|Daly|2015|pp=[https://link.springer.com/chapter/10.1057/9781137344557_1 11–12]}} | {{harvnb|Berto|Plebani|2015|p=35}} }}</ref> These principles can be used as the [[Axiom|foundation]] on which an ontological system is built and expanded using [[deductive reasoning]].<ref>{{multiref | {{harvnb|Goldenbaum|loc=Lead Section, § 1. The Geometrical Method}} | {{harvnb|Leuenberger|2017|p=[https://books.google.com/books?id=uBBADwAAQBAJ&pg=PT57 57]}} }}</ref> A further intuition-based method relies on [[thought experiment]]s to evoke new intuitions. This happens by imagining a situation relevant to an ontological issue and then employing [[counterfactual thinking]] to assess the consequences of this situation.<ref>{{multiref | {{harvnb|Tahko|2015|pp=177–178}} | {{harvnb|Robinson|2004|pp=537–538, 541–542}} | {{harvnb|Brown|Fehige|2019|loc=Lead Section}} | {{harvnb|Goffi|Roux|2011|pp=[https://philpapers.org/rec/GOFOTV 165, 168–169]}} }}</ref> For example, some ontologists examine the relation between mind and matter by imagining [[philosophical zombies|creatures identical to humans but without consciousness]].<ref>{{harvnb|Kirk|2023|loc=Lead Section, § 2. Zombies and Physicalism}}</ref>

[[Naturalism (philosophy)#Methodological naturalism|Naturalistic methods]] rely on the insights of the natural sciences to determine what exists.<ref>{{multiref | {{harvnb|Berto|Plebani|2015|p=3}} | {{harvnb|Ney|2014|pp=30–31}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} }}</ref> According to an influential approach by [[Willard Van Orman Quine]], ontology can be conducted by analyzing{{efn|An essential step in Quine's analysis is to translate the theory into [[first-order logic]] to make its ontological assumptions explicit.<ref>{{multiref | {{harvnb|Ney|2014|pp=40–41}} | {{harvnb|Göhner|Steinbrink|2018|pp=[https://books.google.com/books?id=FuBLDwAAQBAJ&pg=PA48 48]}} }}</ref>}} the ontological commitments of scientific theories. This method is based on the idea that scientific theories provide the most reliable description of reality and that their power can be harnessed by investigating the ontological assumptions underlying them.<ref>{{multiref | {{harvnb|Ney|2014|pp=37–38, 40–43}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} | {{harvnb|Vineberg|2013|p=[https://books.google.com/books?id=0NJavSp-DbwC&pg=PA133 133]}} }}</ref>

[[File:Guillaume Occam.jpg|thumb|upright=.8|alt=Portrait of William of Ockham|[[William of Ockham]] proposed [[Ockham's Razor]], a principle to decide between competing theories.]]

Principles of theory choice offer guidelines for assessing the advantages and disadvantages of ontological theories rather than guiding their construction.<ref>{{multiref | {{harvnb|Effingham|2013|loc=§ Methodology: Theory choice}} | {{harvnb|Göhner|Steinbrink|2018|pp=[https://books.google.com/books?id=FuBLDwAAQBAJ&pg=PA57 57–58]}} }}</ref> The principle of [[Ockham's Razor]] says that simple theories are preferable.<ref>{{multiref | {{harvnb|Ney|2014|pp=48–49}} | {{harvnb|Jacquette|2014|pp=[https://books.google.com/books?id=NmPfBQAAQBAJ&pg=PA207 207–208]}} }}</ref> A theory can be simple in different respects, for example, by using very few basic types or by describing the world with a small number of fundamental entities.<ref>{{multiref | {{harvnb|Effingham|2013|loc=§ Methodology: Ontological parsimony}} | {{harvnb|Brenner|2024|pp=[https://books.google.com/books?id=L3n1EAAAQBAJ&pg=PA20 20–21]}} | {{harvnb|Göhner|Steinbrink|2018|p=[https://books.google.com/books?id=FuBLDwAAQBAJ&pg=PA58 58]}} }}</ref> Ontologists are also interested in the explanatory power of theories and give preference to theories that can explain many observations.<ref>{{multiref | {{harvnb|Effingham|2013|loc=§ Methodology: Ontological parsimony}} | {{harvnb|Göhner|Steinbrink|2018|p=[https://books.google.com/books?id=FuBLDwAAQBAJ&pg=PA59 59]}} }}</ref> A further factor is how close a theory is to [[common sense]]. Some ontologists use this principle as an argument against theories that are very different from how ordinary people think about the issue.<ref>{{multiref | {{harvnb|Effingham|2013|loc=§ Methodology: Coherence with Intuitions}} | {{harvnb|Berto|Plebani|2015|p=35}} }}</ref>

In applied ontology, [[ontological engineering]] is the process of creating and refining conceptual models of specific domains.<ref>{{multiref | {{harvnb|Grenon|2008|p=70}} | {{harvnb|Gómez-Pérez|Fernández-López|Corcho|2006|pp=v, 195}} | {{harvnb|Fernández-López|Gómez-Pérez|2002|p=129}} }}</ref> Developing a new ontology from scratch involves various preparatory steps, such as delineating the scope of the domain one intends to model and specifying the purpose and use cases of the ontology. Once the foundational concepts within the area have been identified, ontology engineers proceed by defining them and characterizing the relations between them. This is usually done in a [[formal language]] to ensure precision and, in some cases, automatic [[computability]]. In the following review phase, the validity of the ontology is assessed using test data.<ref>{{multiref | {{harvnb|Kendall|McGuinness|2022|pp=47–49}} | {{harvnb|Gómez-Pérez|Fernández-López|Corcho|2006|pp=109–110}} }}</ref> Various more specific instructions for how to carry out the different steps have been suggested. They include the [[Cyc]] method, Grüninger and Fox's methodology, and so-called METHONTOLOGY.<ref>{{multiref | {{harvnb|Gómez-Pérez|Fernández-López|Corcho|2006|pp=153, 195}} | {{harvnb|Babkin|Ulitin|2024|p=[https://books.google.com/books?id=A37lEAAAQBAJ&pg=PA28 28]}} | {{harvnb|Fernández-López|Gómez-Pérez|2002|p=129}} }}</ref> In some cases, it is feasible to adapt a pre-existing ontology to fit a specific domain and purpose rather than creating a new one from scratch.<ref>{{multiref | {{harvnb|Gómez-Pérez|Fernández-López|Corcho|2006|pp=112–113}} | {{harvnb|Fernández-López|Gómez-Pérez|2002|p=129}} }}</ref>

== Related fields ==
Ontology overlaps with many disciplines, including [[logic]], the study of [[Logical reasoning|correct reasoning]].<ref>{{harvnb|Hofweber|2023|loc=Lead Section, § 2.1 Different conceptions of logic}}</ref> Ontologists often employ [[Formal system|logical systems]] to express their insights, specifically in the field of formal ontology. Of particular interest to them is the [[existential quantifier]] (<math>\exists</math>), which is used to express what exists. In [[first-order logic]], for example, the formula <math>\exists x \text{Dog}(x)</math> states that dogs exist.<ref>{{multiref | {{harvnb|Cook|2009|pp=[https://books.google.com/books?id=JfaqBgAAQBAJ&pg=PA112 112–113]}} | {{harvnb|Casati|Fujikawa|loc=Lead Section, §1. Existence as a Second-Order Property and Its Relation to Quantification}} | {{harvnb|Albertazzi|1996|p=206}} }}</ref> Some philosophers study ontology by examining the structure of thought and language, saying that they reflect the structure of being.<ref>{{harvnb|Hofweber|2023|loc=§ 4.6 The form of thought and the structure of reality. (L4) meets (O3)}}</ref> Doubts about the accuracy of [[natural language]] have led some ontologists to seek a new [[formal language]], termed ''ontologese'', for a better representation of the fundamental structure of reality.<ref>{{multiref | {{harvnb|Hofweber|2023|loc=§ 4.5 The fundamental language. (L1) meets (O4) and (the new beginning of?) (O2)}} | {{harvnb|Hofweber|2021|p=[https://books.google.com/books?id=lEwwEAAAQBAJ&pg=PA89 89]}} }}</ref>

{{cladogram
|title=Suggested Upper Merged Ontology
|caption=Fundamental categories in the [[Suggested Upper Merged Ontology]]<ref>{{harvnb|Heckmann|2006|p=[https://books.google.com/books?id=e5adLEi4gYgC&pg=PA42 42]}}</ref>
|cladogram={{clade
    |label1=Entity{{nbsp}}{{nbsp}}{{nbsp}}{{nbsp}}
    |1={{clade
        |label1={{nbsp}}{{nbsp}}Physical{{nbsp}}{{nbsp}}{{nbsp}}{{nbsp}}
        |1={{clade
            |label1={{nbsp}}{{nbsp}}Object
            |1={{nbsp}}
            |label2={{nbsp}}{{nbsp}}Process
            |2={{nbsp}}
            }}
        |label2={{nbsp}}{{nbsp}}Abstract{{nbsp}}{{nbsp}}{{nbsp}}{{nbsp}}
        |2={{clade
            |label1={{nbsp}}{{nbsp}}Quantity    
            |1={{nbsp}}
            |label2={{nbsp}}{{nbsp}}Proposition
            |2={{nbsp}}
            |label3={{nbsp}}{{nbsp}}Attribute
            |3={{nbsp}}
            |label4={{nbsp}}{{nbsp}}Relation
            |4={{nbsp}}
            |label5={{nbsp}}{{nbsp}}Set or Class
            |5={{nbsp}}
        }}
    }}
}}
}}

Ontologies are often used in information science to provide a conceptual scheme or inventory of a specific domain, making it possible to classify objects and formally represent information about them. This is of specific interest to computer science, which builds [[database]]s to store this information and defines computational processes to automatically transform and use it.<ref>{{multiref | {{harvnb|Grütter|Bauer-Messmer|2007|p=[https://books.google.com/books?id=-mv0098rs-oC&pg=PA350 350]}} | {{harvnb|Hawley|2016|pp=168–170}} }}</ref> For instance, to encode and store information about clients and employees in a database, an organization may use an ontology with categories such as person, company, address, and name.<ref>{{harvnb|Kozierkiewicz|Pietranik|2019|p=[https://books.google.com/books?id=2uWPDwAAQBAJ&pg=PA24 24]}}</ref> In some cases, it is necessary to exchange information belonging to different domains or to integrate databases using distinct ontologies. This can be achieved with the help of [[Upper ontology|upper ontologies]], which are not limited to one specific domain. They use general categories that apply to most or all domains, like [[Suggested Upper Merged Ontology]] and [[Basic Formal Ontology]].<ref>{{multiref | {{harvnb|Hameed|Preece|Sleeman|2013|pp=[https://books.google.com/books?id=uTwDCAAAQBAJ&pg=PA232 231–233]}} | {{harvnb|Stuart|2016|p=[https://books.google.com/books?id=awYUDgAAQBAJ&pg=PA14 14]}} }}</ref>

Similar applications of ontology are found in various fields seeking to manage extensive information within a structured framework. [[Protein Ontology]] is a formal framework for the standardized representation of [[protein]]-related entities and their relationships.<ref>{{multiref | {{harvnb|Chicco|Masseroli|2018|pp=[https://books.google.com/books?id=rs51DwAAQBAJ&pg=PA832 832]}} | {{harvnb|Masseroli|2018|p=[https://books.google.com/books?id=rs51DwAAQBAJ&pg=PA814 814]}} }}</ref> [[Gene Ontology]] and [[Sequence Ontology]] serve a similar purpose in the field of [[genetics]].<ref>{{harvnb|Masseroli|2018|p=[https://books.google.com/books?id=rs51DwAAQBAJ&pg=PA814 814]}}</ref> Environment Ontology is a knowledge representation focused on [[ecosystems]] and environmental processes.<ref>{{harvnb|Pouchard|Devarakon|Bransetter|2015|pp=[https://books.google.com/books?id=pmVrCgAAQBAJ&pg=PA37 37–38]}}</ref> [[FOAF|Friend of a Friend]] provides a conceptual framework to represent relations between people and their interests and activities.<ref>{{harvnb|Yu|2014|pp=[https://books.google.com/books?id=vcmoBQAAQBAJ&pg=PA357 357–359]}}</ref>

The topic of ontology has received increased attention in [[anthropology]] since the 1990s, sometimes termed the "[[ontological turn]]".<ref>{{harvnb|Scott|2013|pp=[https://www.jstor.org/stable/42001687 859–872]}}</ref> This type of inquiry is focused on how people from different cultures experience and understand the nature of being. Specific interest has been given to the ontological outlook of [[Indigenous people]] and how it differs from a Western perspective.<ref>{{multiref | {{harvnb|Scott|2013|pp=[https://www.jstor.org/stable/42001687 859–872]}} | {{harvnb|Heywood|2012|pp=[https://www.jstor.org/stable/43610895 143–151]}} }}</ref> As an example of this contrast, it has been argued that various indigenous communities ascribe [[intentionality]] to non-human entities, like plants, forests, or rivers. This outlook is known as [[animism]]<ref>{{harvnb|Ludwig|Weiskopf|2019}}</ref> and is also found in [[Indigenous peoples of the Americas|Native American]] ontologies, which emphasize the interconnectedness of all living entities and the importance of balance and harmony with nature.<ref>{{multiref | {{harvnb|Pack|2023|pp=105–107|loc=Animist Ontologies, Abstraction, and Slavery}} | {{harvnb|Pack|2022|pp=[https://books.google.com/books?id=nP18EAAAQBAJ&pg=PA162 162–163]}} | {{harvnb|Sinclair|2022|p=96|loc=Righting Names: The Importance of Native American Philosophies of Naming for Environmental Justice}} }}</ref>

Ontology is closely related to [[theology]] and its interest in the [[existence of God]] as an ultimate entity. The [[ontological argument]], first proposed by [[Anselm of Canterbury]], attempts to prove the existence of the divine. It defines [[God]] as the greatest conceivable being. From this definition it concludes that God must exist since God would not be the greatest conceivable being if God lacked existence.<ref>{{multiref | {{harvnb|Grayling|2019|loc=Anselm}} | {{harvnb|Dehsen|2013|p=[https://books.google.com/books?id=cU7cAAAAQBAJ&pg=PA10 10]}} }}</ref> Another overlap in the two disciplines is found in ontological theories that use God or an ultimate being as the foundational principle of reality. Heidegger criticized this approach, terming it ''[[ontotheology]]''.<ref>{{multiref | {{harvnb|Halteman|1998|loc=Lead Section}} | {{harvnb|Thomson|2011|p=[https://books.google.com/books?id=S1JS4X_1ORgC&pg=PA114 114]}} }}</ref>

== History ==
{{main|History of ontology}}

[[File:Kapila (cropped).png|thumb|upright=.8|alt=Depiction of Kapila|[[Kapila]] was one of the founding fathers of the dualist school of [[Samkhya]].<ref>{{harvnb|Ruzsa|loc=§ 1. History}}</ref>]]

The roots of ontology in [[ancient philosophy]] are speculations about the nature of being and the source of the universe. Discussions of the essence of reality are found in the [[Upanishads]], ancient Indian scriptures dating from as early as 700 BCE. They say that the universe has a divine foundation and discuss in what sense [[Brahman|ultimate reality]] is one or many.<ref>{{multiref | {{harvnb|Baird|2017|p=[https://books.google.com/books?id=Am1QDwAAQBAJ&pg=PA5 5]}} | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} }}</ref> [[Samkhya]], the first [[Āstika and nāstika|orthodox school of Indian philosophy]],{{efn|Its initial ideas were developed in the 7th and 6th centuries BCE but it was not until 350 CE that it received its classical and systematic formulation.<ref>{{multiref | {{harvnb|Ruzsa|loc=Lead Section}} | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} }}</ref>}} formulated an [[atheist]] dualist ontology based on the Upanishads, identifying [[Purusha|pure consciousness]] and [[Prakriti|matter]] as its two foundational principles.<ref>{{multiref | {{harvnb|Lopez|2010|p=[https://books.google.com/books?id=qejaEAAAQBAJ&pg=PA1426 1426]}} | {{harvnb|Ruzsa|loc=Lead Section}} | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} }}</ref> The later [[Vaisheshika]] school{{efn|The founding text of the school was written 500–300 BCE and the first major commentary on it is dated 400 CE.<ref>{{harvnb|Lopez|2010|p=[https://books.google.com/books?id=qejaEAAAQBAJ&pg=PA1426 1426]}}</ref>}} proposed a comprehensive system of categories.<ref>{{multiref | {{harvnb|Ambuel|1998|loc=§ 1. Categories}} | {{harvnb|Lopez|2010|p=[https://books.google.com/books?id=qejaEAAAQBAJ&pg=PA1426 1426]}} }}</ref> In [[ancient China]], [[Laozi]]'s (6th century BCE){{efn|The exact date is disputed and some theorists suggest a later date between the 4th and 3rd centuries BCE.<ref>{{multiref | {{harvnb|Dynes|2016|p=[https://books.google.com/books?id=pxjOEAAAQBAJ&pg=PA60 60]}} | {{harvnb|Littlejohn|loc=§ 2. Classical Sources for Our Understanding of Daoism}} }}</ref>}} [[Taoism]] examines the underlying order of the universe, known as [[Tao]], and how this order is shaped by the interaction of two basic forces, [[yin and yang]].<ref>{{multiref | {{harvnb|Littlejohn|loc=§ 5. Fundamental Concepts in the Daodejing}} | {{harvnb|Dynes|2016|pp=[https://books.google.com/books?id=pxjOEAAAQBAJ&pg=PA60 60–61]}} }}</ref> The philosophical movement of [[Xuanxue]] emerged in the 3rd century CE and explored the relation between being and non-being.<ref>{{multiref | {{harvnb|Chai|2020|p=[https://books.google.com/books?id=LSAAEAAAQBAJ&pg=PA19 19]}} | {{harvnb|Robinet|2013|loc=[https://books.google.com/books?id=R3Sp6TfzhpIC&pg=PA274 Chongxuan]}} }}</ref>

Starting in the 6th century BCE, [[Presocratic philosophy|Presocratic philosophers]] in [[ancient Greece]] aimed to provide rational explanations of the universe. They suggested that a first principle, such as water or fire, is the primal source of all things.<ref>{{multiref | {{harvnb|Graham|loc=§ 1. Presocratic Thought}} | {{harvnb|Rée|Urmson|2004|pp=[https://books.google.com/books?id=uewoLyIw_DQC&pg=PA308 308–309]}} }}</ref> [[Parmenides]] (c. 515–450 BCE) is sometimes considered the founder of ontology because of his explicit discussion of the concepts of being and non-being.<ref>{{multiref | {{harvnb|Kahn|2009|p=[https://books.google.com/books?id=DxE6zOaaGyIC&pg=PA143 143]}} | {{harvnb|Graham|loc=§ 6.a. Parmenides}} }}</ref> Inspired by Presocratic philosophy, [[Plato]] (427–347 BCE) developed his [[theory of forms]]. It distinguishes between unchangeable perfect forms and matter, which has a lower degree of existence and imitates the forms.<ref>{{multiref | {{harvnb|Hancock|2006|pp=184–185}} | {{harvnb|Hamlyn|2005|p=590}} | {{harvnb|Graham|loc=§ 3b. Metaphysics}} }}</ref> [[Aristotle]] (384–322 BCE) suggested an elaborate system of categories that introduced the concept of substance as the primary kind of being.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=§ 1.1 Aristotelian Realism}} | {{harvnb|Studtmann|2024|loc=§ 2. The Ten-Fold Division}} | {{harvnb|Wardy|1998|loc=§ 1. Categories in Aristotle}} }}</ref> The school of [[Neoplatonism]] arose in the 3rd century CE and proposed an ineffable source of everything, called ''the One'', which is more basic than being itself.<ref>{{multiref | {{harvnb|Halfwassen|2014|p=[https://books.google.com/books?id=yhcWBAAAQBAJ&pg=PA185 185]}} | {{harvnb|Hancock|2006|pp=187–188}} | {{harvnb|Hamlyn|2005|pp=590–591}} | {{harvnb|Graham|loc=§ 5. Post-Hellenistic Thought}} }}</ref>

The [[problem of universals]] was an influential topic in medieval ontology. [[Boethius]] (477–524 CE) suggested that universals can exist not only in matter but also in the mind. This view inspired [[Peter Abelard]] (1079–1142 CE), who proposed that universals exist only in the mind.<ref>{{multiref | {{harvnb|Hancock|2006|pp=188–189}} | {{harvnb|Grayling|2019|loc=§ Boethius, § Abelard}} | {{harvnb|Marenbon|2009|p=[https://books.google.com/books?id=DYSVbvnDL8IC&pg=PA6 6]}} | {{harvnb|Sweeney|2016|pp=[https://books.google.com/books?id=orIYDAAAQBAJ&pg=PA10 10–11]}} }}</ref> [[Thomas Aquinas]] (1224–1274 CE) developed and refined fundamental ontological distinctions, such as the contrast between existence and [[essence]], between substance and accidents, and between [[matter and form]].<ref>{{multiref | {{harvnb|Buren|2023|p=[https://books.google.com/books?id=qnWzEAAAQBAJ&pg=PA53 53]}} | {{harvnb|Hancock|2006|p=189}} }}</ref> He also discussed the [[transcendentals]], which are the most general properties or modes of being.<ref>{{multiref | {{harvnb|Aertsen|2009|p=[https://books.google.com/books?id=lQ2xDwAAQBAJ&pg=PA117 117]}} | {{harvnb|Goris|Aertsen|2019|loc=§ 4.1 The first model: God as the cause of transcendental being (Thomas Aquinas)}} | {{harvnb|Kuhlmann|2010|p=1859}} }}</ref> [[John Duns Scotus]] (1266–1308) argued that all entities, including God, [[Univocity of being|exist in the same way]] and that each entity has a unique essence, called [[haecceity]].<ref>{{multiref | {{harvnb|Gilson|2018|loc=§ 1C Common Being, § 6C Unity of the Concrete}} | {{harvnb|Williams|2022|loc=§ 2.3 Divine Infinity and the Doctrine of Univocity, § 3.3 Universals and Individuation}} }}</ref> [[William of Ockham]] (c. 1287–1347 CE) proposed that one can decide between competing ontological theories by assessing which one uses the smallest number of elements, a principle known as [[Ockham's razor]].<ref>{{multiref | {{harvnb|Hancock|2006|p=190}} | {{harvnb|Grayling|2019|loc=§ Ockham}} | {{harvnb|Kuhlmann|2010|p=1859b}} }}</ref>

[[File:Zhu_xi.jpg|thumb|upright=.8|alt=Depiction of Zhu Xi|The [[Neo-Confucianism|Neo-Confucian]] philosopher [[Zhu Xi]] conceived the concept of [[Li (neo-Confucianism)|li]] as the organizing principle of the universe.<ref>{{harvnb|Thompson|2021|loc=§ 4. Natural Philosophy}}</ref>]]

In [[Islamic philosophy|Arabic-Persian philosophy]], [[Avicenna]] (980–1037 CE) combined ontology with [[theology]]. He identified God as a necessary being that is the source of everything else, which only has contingent existence.<ref>{{harvnb|Lizzini|2021|loc=§ 2.1 Ontology and Theology, § 2.4 Univocacy of Being and Ontological Distinction}}</ref> In 8th-century [[Indian philosophy]], the school of [[Advaita Vedanta]] emerged. It says that only a single all-encompassing entity exists, stating that the impression of a plurality of distinct entities is an [[Maya (religion)|illusion]].<ref>{{multiref | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} | {{harvnb|Perrett|2016|loc=§ The Medieval Period of Indian Philosophy}} | {{harvnb|Dalal|2021|loc=Lead Section, § 2.3 Two-Tiered Reality}} }}</ref> Starting in the 13th century CE, the [[Navya-Nyāya]] school built on Vaisheshika ontology with a particular focus on the problem of non-existence and negation.<ref>{{multiref | {{harvnb|Ambuel|1998|loc=§ 10. Nonexistence or absence}} | {{harvnb|Bhattacharya|2013|p=[https://books.google.com/books?id=mioW_kp5gzUC&pg=PA35 35]}} }}</ref> 9th-century China saw the emergence of [[Neo-Confucianism]], which developed the idea that a rational principle, known as ''[[Li (neo-Confucianism)|li]]'', is the ground of being and order of the cosmos.<ref>{{multiref | {{harvnb|Berthrong|loc=Lead Section, § 4. Traits, Themes and Motifs}} | {{harvnb|Wu|2022|p=[https://books.google.com/books?id=zRVmEAAAQBAJ&pg=PA56 56]}} | {{harvnb|Smart|2008|p=99}}}}</ref>

[[René Descartes]] (1596–1650) formulated a dualist ontology at the beginning of the modern period. It distinguishes between mind and matter as distinct substances that causally interact.<ref>{{multiref | {{harvnb|Hamlyn|2005|p=591}} | {{harvnb|Dehsen|2013|p=[https://books.google.com/books?id=cU7cAAAAQBAJ&pg=PA51 51]}} }}</ref> Rejecting Descartes's dualism, [[Baruch Spinoza]] (1632–1677) proposed a monist ontology according to which there is only a single entity that is identical to [[God or Nature|God and nature]].<ref>{{multiref | {{harvnb|Hancock|2006|p=190}} | {{harvnb|Hamlyn|2005|p=591}} }}</ref> [[Gottfried Wilhelm Leibniz]] (1646–1716), by contrast, said that the universe is made up of many simple substances, which are synchronized but do not interact with one another.<ref>{{multiref | {{harvnb|Hancock|2006|pp=190–191}} | {{harvnb|Hamlyn|2005|p=591}} | {{harvnb|Look|2020|loc=§ 4. Metaphysics: A Primer on Substance}} | {{harvnb|Menzel|2023|loc=1. Possible Worlds and Modal Logic}} }}</ref> [[John Locke]] (1632–1704) proposed his substratum theory, which says that each object has a featureless substratum that supports the object's properties.<ref>{{multiref | {{harvnb|Robinson|Weir|2024|loc=§ 2.5.1 Locke on 'pure substance in general'}} | {{harvnb|Kuhlmann|2010|p=1860b}} }}</ref>  [[Christian Wolff (philosopher)|Christian Wolff]] (1679–1754) was influential in establishing ontology as a distinct discipline, delimiting its scope from other forms of metaphysical inquiry.<ref>{{multiref | {{harvnb|Svare|2006|p=[https://books.google.com/books?id=60MsUE3K2ekC&pg=PA15 15]}} | {{harvnb|Hettche|Dyck|2019|loc=§ 5. Metaphysics}} }}</ref> [[George Berkeley]] (1685–1753) developed an idealist ontology according to which material objects are ideas perceived by minds.<ref>{{multiref | {{harvnb|Hancock|2006|p=192}} | {{harvnb|Hamlyn|2005|p=591}} }}</ref>

[[Immanuel Kant]] (1724–1804) rejected the idea that humans can have direct knowledge of independently existing things and their nature, limiting knowledge to the field of appearances. For Kant, ontology does not study external things but provides a system of [[Category (Kant)|pure concepts of understanding]].<ref>{{multiref | {{harvnb|Lorini|2015|pp=[https://books.google.com/books?id=rY1mCwAAQBAJ&pg=PA71 71, 75–76]}} | {{harvnb|Grier|2022|loc=§ 1. Preliminary Remarks: The Rejection of Ontology (general metaphysics) and the Transcendental Analytic}} }}</ref> Influenced by Kant's philosophy, [[Georg Wilhelm Friedrich Hegel]] (1770–1831) linked ontology and [[logic]]. He said that being and thought are identical and examined their foundational structures.<ref>{{multiref | {{harvnb|Redding|2020|loc=§ 3.1.2 Science of Logic}} | {{harvnb|Houlgate|2006|p=[https://books.google.com/books?id=Xz30HFjrIFAC&pg=PA117 117]}} }}</ref> [[Arthur Schopenhauer]] (1788–1860) rejected Hegel's philosophy and proposed that the world is an expression of a [[Voluntarism (philosophy)#Metaphysical voluntarism|blind and irrational will]].<ref>{{multiref | {{harvnb|Grayling|2019|loc=§ Schopenhauer}} | {{harvnb|Janaway|1999|pp=[https://academic.oup.com/book/2954/chapter-abstract/143638920?redirectedFrom=fulltext 248–249]}} }}</ref> [[Francis Herbert Bradley]] (1846–1924) saw absolute spirit as the ultimate and all-encompassing reality<ref>{{multiref | {{harvnb|Hancock|2006|p=193}} | {{harvnb|Hamlyn|2005|p=592}} | {{harvnb|Grayling|2019|loc=§ Idealism}} }}</ref> while denying that there are any external relations.<ref>{{harvnb|Johansson|2014|p=[https://books.google.com/books?id=Q31HBAAAQBAJ&pg=PA226 226]}}</ref> In Indian philosophy, [[Swami Vivekananda]] (1863–1902) expanded on Advaita Vedanta, emphasizing the unity of all existence.<ref>{{harvnb|Banhatti|1995|p=[https://books.google.com/books?id=jK5862eV7_EC&pg=PA151 151]}}</ref> [[Sri Aurobindo]] (1872–1950) sought to understand the world as an evolutionary manifestation of a divine consciousness.<ref>{{multiref | {{harvnb|Vernekar|1998|pp=81–86}} | {{harvnb|Lawrence|2018|p=415}} | {{harvnb|Phillips|1998|loc=Lead section, § Metaphysics}} }}</ref>

At the beginning of the 20th century, [[Edmund Husserl]] (1859–1938) developed [[Phenomenology (philosophy)|phenomenology]] and employed its method, the description of [[experience]], to address ontological problems.<ref>{{harvnb|Boedeker|2008|p=[https://books.google.com/books?id=mhiAcSw201kC&pg=PA156 156]}}</ref> This idea inspired his student [[Martin Heidegger]] (1889–1976) to clarify the meaning of being by exploring the mode of human existence.<ref>{{multiref | {{harvnb|Wheeler|2020|loc=§ 2.2.1 The Question}} | {{harvnb|Schalow|2019|p=[https://books.google.com/books?id=nJ27DwAAQBAJ&pg=PA139 139]}} }}</ref> [[Jean-Paul Sartre]] responded to Heidegger's philosophy by examining the relation between being and [[nothingness]] from the perspective of human existence, freedom, and consciousness.<ref>{{harvnb|Onof|loc=Lead Section}}</ref> Based on the phenomenological method, [[Nicolai Hartmann]] (1882–1950) developed a complex hierarchical ontology that divides reality into four levels: inanimate, biological, psychological, and spiritual.<ref>{{multiref | {{harvnb|Poli|2011|pp=[https://books.google.com/books?id=1Qya55bssVQC&pg=PA1 1, 11, 21–22]}} | {{harvnb|Peterson|Poli|2022|loc=§ 3. What is the Relationship between Thinking and Being?, § 5.2 Strata}} }}</ref>

[[File:Alexius Meinong 1900.jpg|thumb|upright=.8|alt=Photo of Alexius Meinong|[[Alexius Meinong]] proposed that there are [[nonexistent objects]].]]

[[Alexius Meinong]] (1853–1920) articulated a controversial ontological theory that includes nonexistent objects as part of being.<ref>{{harvnb|Aspenson|2016|loc=[https://books.google.com/books?id=pp4YDQAAQBAJ&pg=PA13 § 1.4 Essential Terms of Metaphysics: Ontology]}}</ref> Arguing against this theory, [[Bertrand Russell]] (1872–1970) formulated a fact ontology known as [[logical atomism]]. This idea was further refined by the early [[Ludwig Wittgenstein]] (1889–1951) and inspired [[D. M. Armstrong]]'s (1926–2014) ontology.<ref>{{multiref | {{harvnb|Proops|2022|loc=Lead Section}} | {{harvnb|Klement|2019|loc=Lead Section}} | {{harvnb|Mumford|2003|p=[https://books.google.com/books?id=kGGmBgAAQBAJ&pg=PA100 100]}} | {{harvnb|Loux|Crisp|2017|p=148}} }}</ref> [[Alfred North Whitehead]] (1861–1947), by contrast, developed a process ontology.<ref>{{multiref|{{harvnb|Desmet|Irvine|2022|loc=§ 6. Metaphysics}}|{{harvnb|Palmer|1998|p=[https://books.google.com/books?id=ZT2pI9IMiYUC&pg=PA175 175]}}}}</ref> [[Rudolf Carnap]] (1891–1970) questioned the objectivity of ontological theories by claiming that what exists depends on one's linguistic framework.<ref>{{multiref | {{harvnb|Chalmers|2009|p=78}} | {{harvnb|Hofweber|2023|loc=§ 4.4 Carnap’s rejection of ontology. (L1) meets (O4) and (the end of?) (O2)}} }}</ref> He had a strong influence on [[Willard Van Orman Quine]] (1908–2000), who analyzed the ontological commitments of scientific theories to solve ontological problems.<ref>{{multiref | {{harvnb|Ney|2014|pp=37–38, 40}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} }}</ref> Quine's student [[David Lewis (philosopher)|David Lewis]] (1941–2001) formulated the position of modal realism, which says that possible worlds are as real and concrete as the actual world.<ref>{{harvnb|Parent|loc=§ 2. Lewis' Realism}}</ref> Since the end of the 20th century, interest in applied ontology has risen in computer and information science with the development of conceptual frameworks for specific domains.<ref>{{multiref | {{harvnb|Guizzardi|2007|pp=[https://books.google.com/books?id=kR2iUt-CuwMC&pg=PA18 18–19]}} | {{harvnb|Sales|Guizzardi|2017|p=[https://books.google.com/books?id=F9s1DwAAQBAJ&pg=PA28 28]}} }}</ref>

== See also ==
{{cols}}
* {{annotated link|Hauntology}}
{{colend}}

== References ==
=== Notes ===
{{notelist}}

=== Citations ===
{{Reflist}}

=== Sources ===
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* {{cite book |last1=Kim |first1=Jaegwon |title=The Oxford Companion to Philosophy |publisher=Oxford University Press |isbn=978-0-19-926479-7 |url=https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1608?rskey=jqUtkA&result=1601 |language=en |chapter=Mind, Problems of the Philosophy of |date=2005 |access-date=29 March 2024 |archive-date=11 April 2024 |archive-url=https://web.archive.org/web/20240411165434/https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1608?rskey=jqUtkA&result=1601 |url-status=live }}
* {{cite web |last1=Kirk |first1=Robert |title=Zombies |url=https://plato.stanford.edu/entries/zombies/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=15 March 2024 |date=2023 |archive-date=28 September 2020 |archive-url=https://web.archive.org/web/20200928081213/https://plato.stanford.edu/entries/zombies/ |url-status=live }}
* {{cite book |last1=Kirwan |first1=Christopher |title=The Oxford Companion to Philosophy |publisher=Oxford University Press |isbn=978-0-19-926479-7 |url=https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1171 |language=en |chapter=Identity |date=2005 |access-date=29 March 2024 |archive-date=11 April 2024 |archive-url=https://web.archive.org/web/20240411165535/https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1171 |url-status=live }}
* {{cite web |last1=Klement |first1=Kevin |title=Russell's Logical Atomism |url=https://plato.stanford.edu/entries/logical-atomism/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=2 April 2024 |date=2019 |archive-date=11 April 2024 |archive-url=https://web.archive.org/web/20240411165434/https://plato.stanford.edu/entries/logical-atomism/ |url-status=live }}
* {{cite book |last1=Koons |first1=Robert C. |last2=Pickavance |first2=Timothy H. |title=Metaphysics: The Fundamentals |date=2015 |publisher=Wiley-Blackwell |isbn=978-1-4051-9574-4 |edition=1}}
* {{cite web |last1=Korman |first1=Daniel Z. |title=Material Constitution |url=https://www.oxfordbibliographies.com/display/document/obo-9780195396577/obo-9780195396577-0386.xml |website=Oxford Bibliographies Online |publisher=Oxford University Press |access-date=3 July 2024 |language=en |doi=10.1093/OBO/9780195396577-0386 |date=2021 |isbn=978-0-19-539657-7 |archive-date=6 July 2024 |archive-url=https://web.archive.org/web/20240706141148/https://www.oxfordbibliographies.com/display/document/obo-9780195396577/obo-9780195396577-0386.xml |url-status=live }}
* {{cite book |last1=Körner |first1=Stephan |title=Metaphysics: Its Structure and Function |date=1984 |publisher=Cambridge University Press |isbn=978-0-521-26496-9 |url=https://books.google.com/books?id=eAA4AAAAIAAJ&pg=PA183 |language=en |access-date=18 March 2024 |archive-date=17 March 2024 |archive-url=https://web.archive.org/web/20240317134336/https://books.google.com/books?id=eAA4AAAAIAAJ&pg=PA183 |url-status=live }}
* {{cite book |last1=Koslicki |first1=Kathrin |title=Form, Matter, Substance |publisher=Oxford University Press |isbn=978-0-19-255708-7 |url=https://books.google.com/books?id=th1rDwAAQBAJ&pg=PA11 |language=en |date=2018 |access-date=2024-06-12 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706141144/https://books.google.com/books?id=th1rDwAAQBAJ&pg=PA11#v=onepage&q&f=false |url-status=live }}
* {{cite book |last1=Kozierkiewicz |first1=Adrianna |last2=Pietranik |first2=Marcin |editor1-last=Nguyen |editor1-first=Ngoc Thanh |editor2-last=Gaol |editor2-first=Ford Lumban |editor3-last=Hong |editor3-first=Tzung-Pei |editor4-last=Trawiński |editor4-first=Bogdan |title=Intelligent Information and Database Systems: 11th Asian Conference, ACIIDS 2019, Yogyakarta, Indonesia, April 8–11, 2019, Proceedings, Part I |publisher=Springer |isbn=978-3-030-14799-0 |chapter-url=https://books.google.com/books?id=2uWPDwAAQBAJ&pg=PA24 |language=en |chapter=A Formal Framework for the Ontology Evolution |date=2019 }}
* {{cite journal |last1=Kriegel |first1=Uriah |title=Intentional Inexistence and Phenomenal Intentionality |journal=Philosophical Perspectives |volume=21 |issue=1 |doi=10.1111/j.1520-8583.2007.00129.x |date=2007 |pages=307–340 |issn=1520-8583 |url=https://philarchive.org/rec/KRIIIA }}
* {{cite web |last1=Kroon |first1=Fred |last2=Voltolini |first2=Alberto |title=Fictional Entities |url=https://plato.stanford.edu/entries/fictional-entities/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=28 April 2024 |date=2023 |archive-date=June 17, 2024 |archive-url=https://web.archive.org/web/20240617060209/https://plato.stanford.edu/entries/fictional-entities/ |url-status=live }}
* {{cite book |last1=Kuhlmann |first1=Meinard |editor1-last=Sandkühler |editor1-first=Hans Jörg |title=Enzyklopädie Philosophie |publisher=Meiner |isbn=978-3-7873-1999-2 |edition=2 |chapter=Ontologie |date=2010 }}
* {{cite book |last1=Kuhn |first1=Thomas S. |editor1-last=Sture |editor1-first=Allén |title=Possible Worlds in Humanities, Arts and Sciences: Proceedings of Nobel Symposium 65 |date=2010 |publisher=Walter de Gruyter |isbn=978-3-11-086685-8 |chapter-url=https://books.google.com/books?id=c_eYe6NVaDMC&pg=PA13 |language=en |chapter=Possible Worlds in History of Science |access-date=29 March 2024 |archive-date=28 March 2024 |archive-url=https://web.archive.org/web/20240328192319/https://books.google.com/books?id=c_eYe6NVaDMC&pg=PA13 |url-status=live }}
* {{cite book |last1=Kumar |first1=ShashiPrabha |title=Categories, Creation and Cognition in Vaiśeṣika Philosophy |publisher=Springer |isbn=978-981-13-2965-4 |url=https://books.google.com/books?id=Jr2YDwAAQBAJ&pg=PA34 |language=en |date=2019 |access-date=2024-06-12 |archive-date=2024-06-08 |archive-url=https://web.archive.org/web/20240608121137/https://books.google.com/books?id=Jr2YDwAAQBAJ&pg=PA34 |url-status=live }}
* {{cite web |last1=Ladyman |first1=James |title=Structural Realism |url=https://plato.stanford.edu/entries/structural-realism/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=5 June 2024 |date=2023 |archive-date=11 September 2019 |archive-url=https://web.archive.org/web/20190911130111/https://plato.stanford.edu/entries/structural-realism/ |url-status=live }}
* {{cite book |last1=Lamarque |first1=Peter |chapter=Fictional Entities |url=https://www.rep.routledge.com/articles/thematic/fictional-entities/v-1 |title=Routledge Encyclopedia of Philosophy |access-date=24 March 2024 |language=en |date=1998 |doi=10.4324/9780415249126-M021-1 |isbn=978-0-415-25069-6 |publisher=Routledge |archive-date=April 28, 2024 |archive-url=https://web.archive.org/web/20240428121741/https://www.rep.routledge.com/articles/thematic/fictional-entities/v-1 |url-status=live }}
* {{cite book |last1=LaZella |first1=Andrew T. |title=The Singular Voice of Being: John Duns Scotus and Ultimate Difference |publisher=Fordham University Press |isbn=978-0-8232-8459-7 |url=https://books.google.com/books?id=NCqODwAAQBAJ&pg=PA17 |language=en |date=2019 |access-date=2024-07-03 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706141145/https://books.google.com/books?id=NCqODwAAQBAJ&pg=PA17#v=onepage&q&f=false |url-status=live }}
* {{cite book |last1=Lehrer |first1=Keith |editor1-last=Lehrer |editor1-first=Keith |title=Haecceity: An Ontological Essay |publisher=Springer Science & Business Media |isbn=978-0-7923-2438-6 |chapter-url=https://books.google.com/books?id=w590r7cZ8TsC&pg=PR11 |language=en |chapter=Preface |date=1993 |access-date=2024-06-20 |archive-date=2024-06-19 |archive-url=https://web.archive.org/web/20240619170428/https://books.google.com/books?id=w590r7cZ8TsC&pg=PR11 |url-status=live }}
* {{cite book |last1=Leuenberger |first1=Stephan |editor1-last=Sinclair |editor1-first=Mark |title=The Actual and the Possible: Modality and Metaphysics in Modern Philosophy |publisher=Oxford University Press |isbn=978-0-19-108973-2 |chapter-url=https://books.google.com/books?id=uBBADwAAQBAJ&pg=PT57 |language=en |chapter=Wolff's Close Shafe with Fatalism |date=2017 |access-date=2024-06-17 |archive-date=2024-06-16 |archive-url=https://web.archive.org/web/20240616092245/https://books.google.com/books?id=uBBADwAAQBAJ&pg=PT57 |url-status=live }}
* {{cite book |last1=Levine |first1=Michael P. |title=Pantheism: A Non-Theistic Concept of Deity |publisher=Routledge |isbn=978-1-134-91157-8 |url=https://books.google.com/books?id=GAYyLrfsZvUC |language=en |date=2002 |access-date=2024-06-12 |archive-date=2024-06-11 |archive-url=https://web.archive.org/web/20240611165737/https://books.google.com/books?id=GAYyLrfsZvUC |url-status=live }}
* {{cite web |last1=Linnebo |first1=Øystein |title=Platonism in the Philosophy of Mathematics |url=https://plato.stanford.edu/entries/platonism-mathematics/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=2 June 2024 |date=2024 |archive-date=25 November 2018 |archive-url=https://web.archive.org/web/20181125182359/https://plato.stanford.edu/entries/platonism-mathematics/ |url-status=live }}
* {{cite web |last1=Liston |first1=Michael |title=Scientific Realism and Antirealism |url=https://iep.utm.edu/scientific-realism-antirealism/ |website=Internet Encyclopedia of Philosophy |access-date=2 June 2024 |archive-date=14 March 2024 |archive-url=https://web.archive.org/web/20240314000448/https://iep.utm.edu/scientific-realism-antirealism/ |url-status=live }}
* {{cite web |last1=Littlejohn |first1=Ronnie |title=Daoist Philosophy |url=https://iep.utm.edu/daoismdaoist-philosophy/ |website=Internet Encyclopedia of Philosophy |access-date=30 March 2024 |archive-date=29 March 2024 |archive-url=https://web.archive.org/web/20240329075541/https://iep.utm.edu/daoismdaoist-philosophy/ |url-status=live }}
* {{cite web |last1=Lizzini |first1=Olga |title=Ibn Sina's Metaphysics |url=https://plato.stanford.edu/entries/ibn-sina-metaphysics/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=23 June 2024 |date=2021 |archive-date=11 April 2024 |archive-url=https://web.archive.org/web/20240411165434/https://plato.stanford.edu/entries/ibn-sina-metaphysics/ |url-status=live }}
* {{cite web |last1=Look |first1=Brandon C. |title=Gottfried Wilhelm Leibniz |url=https://plato.stanford.edu/entries/leibniz/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=2 April 2024 |date=2020 |archive-date=5 August 2020 |archive-url=https://web.archive.org/web/20200805133308/https://plato.stanford.edu/entries/leibniz/ |url-status=live }}
* {{cite book |last1=Lopez |first1=Carlos |editor1-last=Melton |editor1-first=J. Gordon |editor2-last=Baumann |editor2-first=Martin |title=Religions of the World: A Comprehensive Encyclopedia of Beliefs and Practices |publisher=Bloomsbury |isbn=978-1-59884-204-3 |chapter-url=https://books.google.com/books?id=qejaEAAAQBAJ&pg=PA1426 |language=en |chapter=India, Hinduism in: Medieval Period |date=2010 |access-date=2024-06-26 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706141146/https://books.google.com/books?id=qejaEAAAQBAJ&pg=PA1426#v=onepage&q&f=false |url-status=live }}
* {{cite book |last1=Lorini |first1=Gualtiero |editor1-last=Kauark-Leite |editor1-first=Patricia |editor2-last=Cecchinato |editor2-first=Giorgia |editor3-last=Figueiredo |editor3-first=Virginia De Araujo |editor4-last=Ruffing |editor4-first=Margit |editor5-last=Serra |editor5-first=Alice |title=Kant and the Metaphors of Reason |publisher=Georg Olms Verlag |isbn=978-3-487-15124-3 |chapter-url=https://books.google.com/books?id=rY1mCwAAQBAJ&pg=PA71 |language=en |chapter=Kant's Metaphor by Analogy Between Ontology and Transcendental Philosophy |date=2015 |access-date=2024-06-26 |archive-date=2024-06-23 |archive-url=https://web.archive.org/web/20240623170222/https://books.google.com/books?id=rY1mCwAAQBAJ&pg=PA71 |url-status=live }}
* {{cite book |last1=Loux |first1=Michael J. |last2=Crisp |first2=Thomas M. |title=Metaphysics: A Contemporary Introduction |date=2017 |publisher=Routledge |isbn=978-1-138-63933-1 |edition=4}}
* {{cite book |last1=Lowe |first1=E. J. |title=The Oxford Companion to Philosophy |publisher=Oxford University Press |isbn=978-0-19-926479-7 |url=https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 |language=en |chapter=Ontology |date=2005 }}
* {{cite book |last1=Lowe |first1=E. J. |title=The Oxford Companion to Philosophy |publisher=Oxford University Press |isbn=978-0-19-926479-7 |url=https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 |language=en |chapter=Being |date=2005a |access-date=2024-06-18 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706141657/https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 |url-status=live }}
* {{cite book |last1=Lowe |first1=E. J. |title=The Oxford Companion to Philosophy |publisher=Oxford University Press |isbn=978-0-19-926479-7 |url=https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 |language=en |chapter=Existence |date=2005b |access-date=2024-06-18 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706141657/https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 |url-status=live }}
* {{cite book |last1=Lowe |first1=E. J. |title=The Four-Category Ontology: A Metaphysical Foundation for Natural Science |publisher=Clarendon Press |isbn=978-0-19-925439-2 |url=https://books.google.com/books?id=s7ISDAAAQBAJ&pg=PA195 |language=en |date=2006 }}
* {{cite journal |last1=Ludwig |first1=David |last2=Weiskopf |first2=Daniel A. |title=Ethnoontology: Ways of World-building Across Cultures |journal=Philosophy Compass |date=2019 |volume=14 |issue=9 |doi=10.1111/phc3.12621 |s2cid=199516840 |quote=Consider the animism debate. Animists consider nonhuman entities (e.g., plants, forests, or rivers) as intentional actors (Harvey, 2005). There is substantial evidence that animism is a widespread metaphysical view. For example, the Nayaka people of South India consider not only certain animals but also stones, hills, cups, and knives to be devaru: beings that stand in active, quasi-social relationships with them (Bird-David, 1999). Devaru are aspects of a larger kin structure that incorporates potential "partners" in the nonhuman world. In addition to these ethnographic observations, there are intriguing cross-cultural similarities in animist ontologies. Indigenous communities around the world tend to be much more permissive in their ascription of intentionality than Western participants (Ojalehto, Douglas, & García, 2017). |doi-access=free}}
* {{cite book |last1=Lupisella |first1=Mark |title=Cosmological Theories of Value: Science, Philosophy, and Meaning in Cosmic Evolution |date=2020 |publisher=Springer Nature |isbn=978-3-030-25339-4 |url=https://books.google.com/books?id=3JTyDwAAQBAJ&pg=PA70 |language=en |access-date=12 June 2024 |archive-date=5 June 2024 |archive-url=https://web.archive.org/web/20240605173449/https://books.google.com/books?id=3JTyDwAAQBAJ&pg=PA70 |url-status=live }}
* {{cite web |last1=MacBride |first1=Fraser |title=Relations |url=https://plato.stanford.edu/entries/relations/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=2 July 2024 |date=2020 |archive-date=6 July 2024 |archive-url=https://web.archive.org/web/20240706141656/https://plato.stanford.edu/entries/relations/ |url-status=live }}
* {{cite book |last1=MacIntyre |first1=Alasdair |editor1-last=Borchert |editor1-first=Donald M. |title=Encyclopedia of Philosophy |publisher=Macmillan Reference USA |isbn=978-0-02-865781-3 |edition=2 |volume=1 |chapter=Being |date=2006 }}
* {{cite web |last1=Mackie |first1=Penelope |title=Existence |url=https://www.rep.routledge.com/articles/thematic/existence/v-1 |website=Routledge Encyclopedia of Philosophy |publisher=Routledge |access-date=7 August 2023 |language=en |date=1998 |archive-date=10 August 2023 |archive-url=https://web.archive.org/web/20230810230551/https://www.rep.routledge.com/articles/thematic/existence/v-1 |url-status=live |issn=2161-0002 }}
* {{cite book |last1=Mackie |first1=Penelope |title=The Oxford Companion to Philosophy |publisher=Oxford University Press |isbn=978-0-19-926479-7 |url=https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 |language=en |chapter=Events |date=2005 |access-date=2024-06-18 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706141657/https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1806 |url-status=live }}
* {{cite web |last1=MacLeod |first1=Mary C. |last2=Rubenstein |first2=Eric M. |title=Universals |url=https://iep.utm.edu/universa/ |website=Internet Encyclopedia of Philosophy |access-date=24 March 2024 |archive-date=24 February 2024 |archive-url=https://web.archive.org/web/20240224193719/https://iep.utm.edu/universa/ |url-status=live }}
* {{cite book |last1=Marenbon |first1=John |editor1-last=Marenbon |editor1-first=John |title=The Cambridge Companion to Boethius |publisher=Cambridge University Press |isbn=978-1-139-82815-4 |chapter-url=https://books.google.com/books?id=DYSVbvnDL8IC&pg=PA6 |language=en |chapter=Introduction: Reading Boethius Whole |date=2009 |access-date=4 April 2024 |archive-date=2 April 2024 |archive-url=https://web.archive.org/web/20240402120923/https://books.google.com/books?id=DYSVbvnDL8IC&pg=PA6 |url-status=live }}
* {{cite web |last1=Marshall |first1=Dan |last2=Weatherson |first2=Brian |title=Intrinsic Vs. Extrinsic Properties |url=https://plato.stanford.edu/entries/intrinsic-extrinsic/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=2 July 2024 |date=2023 |archive-date=6 July 2024 |archive-url=https://web.archive.org/web/20240706140207/https://plato.stanford.edu/entries/intrinsic-extrinsic/ |url-status=live }}
* {{cite book |last1=Masseroli |first1=Marco |title=Encyclopedia of Bioinformatics and Computational Biology: ABC of Bioinformatics |publisher=Elsevier |isbn=978-0-12-811432-2 |chapter-url=https://books.google.com/books?id=rs51DwAAQBAJ&pg=PA813 |language=en |chapter=Biological and Medical Ontologies: Introduction |date=2018 |access-date=2024-06-29 |archive-date=2024-06-28 |archive-url=https://web.archive.org/web/20240628171434/https://books.google.com/books?id=rs51DwAAQBAJ&pg=PA813 |url-status=live }}
* {{cite book |last1=Maurin |first1=Anna-Sofia |title=Routledge Encyclopedia of Philosophy |chapter=Particulars |date=2019 |publisher=Routledge Encyclopedia of Philosophy |chapter-url=https://www.rep.routledge.com/articles/thematic/particulars/v-2/sections/particulars-thick-or-thin |language=en |doi=10.4324/9780415249126-N040-2 |isbn=978-0-415-25069-6 |access-date=29 March 2024 |archive-date=25 March 2024 |archive-url=https://web.archive.org/web/20240325125022/https://www.rep.routledge.com/articles/thematic/particulars/v-2/sections/particulars-thick-or-thin |url-status=live }}
* {{cite book |last1=McLaughlin |first1=Brian P. |editor-last1=Audi |editor-first1=Robert |title=The Cambridge Dictionary of Philosophy |publisher=Cambridge University Press |isbn=978-0-521-63722-0 |edition=2 |date=1999 }}
* {{cite web |last1=Menzel |first1=Christopher |title=Possible Worlds |url=https://plato.stanford.edu/entries/possible-worlds/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=24 March 2024 |date=2023 |archive-date=6 July 2024 |archive-url=https://web.archive.org/web/20240706141659/https://plato.stanford.edu/entries/possible-worlds/ |url-status=live }}
* {{cite web |author1=Merriam-Webster |title=Definition of Ontology |url=https://www.merriam-webster.com/dictionary/ontology |website=Merriam-Webster Dictionary |publisher=Merriam-Webster |access-date=17 June 2024 |language=en |date=2024 |archive-date=6 July 2018 |archive-url=https://web.archive.org/web/20180706190701/https://www.merriam-webster.com/dictionary/ontology |url-status=live }}
* {{cite book |last1=Miller |first1=Kristie |chapter=Persistence |url=https://www.rep.routledge.com/articles/thematic/persistence/v-1/sections/1-four-accounts-of-persistence |title=Routledge Encyclopedia of Philosophy |access-date=26 March 2024 |language=en |doi=10.4324/0123456789-N126-1 |date=2018 |isbn=978-0-415-25069-6 |archive-date=26 March 2024 |archive-url=https://web.archive.org/web/20240326184119/https://www.rep.routledge.com/articles/thematic/persistence/v-1/sections/1-four-accounts-of-persistence |url-status=live |publisher=Routledge }}
* {{cite book |last1=Moore |first1=A. W. |title=Routledge Encyclopedia of Philosophy |chapter=Antirealism in the Philosophy of Mathematics |chapter-url=https://www.rep.routledge.com/articles/thematic/antirealism-in-the-philosophy-of-mathematics/v-1 |publisher=Routledge |access-date=2 June 2024 |language=en |doi=10.4324/9780415249126-Y065-1 |date=1998 |isbn=978-0-415-25069-6 |archive-date=1 June 2024 |archive-url=https://web.archive.org/web/20240601181128/https://www.rep.routledge.com/articles/thematic/antirealism-in-the-philosophy-of-mathematics/v-1 |url-status=live }}
* {{cite book |last1=Mulligan |first1=Kevin |editor1-last=Mulligan |editor1-first=Kevin |title=Language, Truth and Ontology |publisher=Springer Science & Business Media |isbn=978-94-011-2602-1 |chapter-url=https://books.google.com/books?id=oLfwCAAAQBAJ&pg=PR10 |language=en |chapter=Preface |date=2012 |access-date=2024-06-18 |archive-date=2024-06-17 |archive-url=https://web.archive.org/web/20240617175325/https://books.google.com/books?id=oLfwCAAAQBAJ&pg=PR10 |url-status=live }}
* {{cite book |editor-last1=Mumford |editor-first1=Stephen |title=Russell on Metaphysics: Selections from the Writings of Bertrand Russell |publisher=Routledge |isbn=978-1-136-90272-7 |chapter-url=https://books.google.com/books?id=kGGmBgAAQBAJ&pg=PA100 |language=en |chapter=11. The Philosophy of Logical Atomism |date=2003 |access-date=4 April 2024 |archive-date=2 April 2024 |archive-url=https://web.archive.org/web/20240402234006/https://books.google.com/books?id=kGGmBgAAQBAJ&pg=PA100 |url-status=live }}
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* {{cite web |last1=Schaffer |first1=Jonathan |title=Monism |url=https://plato.stanford.edu/entries/monism/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=9 June 2024 |date=2018 |archive-date=6 July 2024 |archive-url=https://web.archive.org/web/20240706142224/https://plato.stanford.edu/entries/monism/ |url-status=live }}
* {{cite book |last1=Schalow |first1=Frank |title=Historical Dictionary of Heidegger's Philosophy |publisher=Rowman & Littlefield |isbn=978-1-5381-2436-9 |url=https://books.google.com/books?id=nJ27DwAAQBAJ&pg=PA139 |language=en |date=2019 |access-date=2024-06-20 |archive-date=2024-06-19 |archive-url=https://web.archive.org/web/20240619170428/https://books.google.com/books?id=nJ27DwAAQBAJ&pg=PA139 |url-status=live }}
* {{cite journal |last=Scott |first=Michael W. |title=The Anthropology of Ontology (Religious Science?) |date=2013 |issue=4 |journal=The Journal of the Royal Anthropological Institute |volume=19 |pages=859–872 |doi=10.1111/1467-9655.12067 |jstor=42001687 |url=https://www.jstor.org/stable/42001687 |quote=Since roughly the 1990s, a growing number of anthropologists have become interested in the study of ontology – the investigation and theorization of diverse experiences and understandings of the nature of being itself. This generally takes the form of ethnographic accounts of indigenous non-Western modes and models of being, presented in more or less explicit contrast with aspects of a Euro-American or modern ontology imputed to conventional anthropology. |access-date=2022-09-24 |archive-date=2022-09-24 |archive-url=https://web.archive.org/web/20220924082557/https://www.jstor.org/stable/42001687 |url-status=live }}
* {{cite journal |last1=Shaffer |first1=Michael J. |title=The Problem of Necessary and Sufficient Conditions and Conceptual Analysis |journal=Metaphilosophy |volume=46 |issue=4–5 |doi=10.1111/meta.12158 |date=2015 |pages=555–563 |url=https://philarchive.org/rec/SHATPO-64 }}
* {{cite book |last1=Shields |first1=Christopher |title=Aristotle |publisher=Routledge |isbn=978-1-317-95214-5 |url=https://books.google.com/books?id=A_pwEAAAQBAJ&pg=PA279 |language=en |date=2014 |access-date=2024-06-18 |archive-date=2024-06-17 |archive-url=https://web.archive.org/web/20240617133338/https://books.google.com/books?id=A_pwEAAAQBAJ&pg=PA279 |url-status=live }}
* {{cite book |last1=Sider |first1=Theodore |editor1-last=Chalmers |editor1-first=David |editor2-last=Manley |editor2-first=David |editor3-last=Wasserman |editor3-first=Ryan |title=Metametaphysics: New Essays on the Foundations of Ontology |publisher=Oxford University Press |isbn=978-0-19-954604-6 |chapter=Ontological Realism |date=2009 }}
* {{cite book |last1=Sider |first1=Theodore |title=Logic for Philosophy |date=2010 |publisher=Oxford University Press |isbn=978-0-19-265881-4 |url=https://books.google.com/books?id=GK8SEAAAQBAJ&pg=PA129 |language=en |access-date=1 September 2023 |archive-date=16 August 2023 |archive-url=https://web.archive.org/web/20230816072051/https://books.google.com/books?id=GK8SEAAAQBAJ&pg=PA129 |url-status=live }}
* {{cite journal |last1=Simons |first1=Peter |title=Ontology Meets Ontologies: Philosophers as Healers |journal=Metascience |volume=18 |issue=3 |doi=10.1007/s11016-009-9308-4 |date=2009 |pages=469–473 }}
* {{cite book |last1=Simons |first1=Peter |editor1-last=Kanzian |editor1-first=Christian |title=Persistence |publisher=Walter de Gruyter |isbn=978-3-11-032705-2 |chapter-url=https://books.google.com/books?id=ql27m77IveQC&pg=PA166 |language=en |chapter=The Thread of Persistence |date=2013 |access-date=29 March 2024 |archive-date=29 March 2024 |archive-url=https://web.archive.org/web/20240329053018/https://books.google.com/books?id=ql27m77IveQC&pg=PA166 |url-status=live }}
* {{cite book |last1=Sinclair |first1=Rebekah |editor1-last=Dhillon |editor1-first=Jaskiran |title=Indigenous Resurgence: Decolonialization and Movements for Environmental Justice |date=2022 |publisher=Berghahn Books |isbn=978-1-80073-247-6 |chapter-url=https://books.google.com/books?id=yhwrEAAAQBAJ&pg=PA96 |language=en |chapter=Righting Names: The Importance of Native American Philosophies of Naming for Environmental Justice |access-date=5 May 2024 |archive-date=7 May 2024 |archive-url=https://web.archive.org/web/20240507030212/https://books.google.com/books?id=yhwrEAAAQBAJ&pg=PA96 |url-status=live }}
* {{cite book |last1=Smart |first1=Ninian |title=World Philosophies |date=2008 |publisher=Routledge |isbn=978-0-415-41188-2 |edition=2}}
* {{cite book |last1=Smith |first1=Barry |last2=Klagges |first2=Bert |editor1-last=Munn |editor1-first=Katherine |editor2-last=Smith |editor2-first=Barry |title=Applied Ontology: An Introduction |publisher=Ontos Verlag |isbn=978-3-938793-98-5 |chapter=Philosophy and Biomedical Information Systems |date=2008 }}
* {{cite web |last1=Sorensen |first1=Roy |title=Nothingness |url=https://plato.stanford.edu/entries/nothingness/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=17 August 2023 |date=2023 |archive-date=30 August 2006 |archive-url=https://web.archive.org/web/20060830021344/https://plato.stanford.edu/entries/nothingness/ |url-status=live }}
* {{cite web |last1=Spear |first1=Andrew D. |title=Husserl, Edmund: Intentionality and Intentional Content |url=https://iep.utm.edu/huss-int/ |website=Internet Encyclopedia of Philosophy |access-date=16 June 2024 |archive-date=16 April 2021 |archive-url=https://web.archive.org/web/20210416164538/https://iep.utm.edu/huss-int/ |url-status=live }}
* {{cite web |last1=Sprigge |first1=T. L. S. |title=Idealism |url=https://www.rep.routledge.com/articles/thematic/idealism/v-1 |website=Routledge Encyclopedia of Philosophy |publisher=Routledge |access-date=9 June 2024 |language=en |date=1998 |archive-date=4 November 2019 |archive-url=https://web.archive.org/web/20191104210304/https://www.rep.routledge.com/articles/thematic/idealism/v-1 |url-status=live }}
* {{cite book |last1=Stuart |first1=David |title=Practical Ontologies for Information Professionals |publisher=Facet Publishing |isbn=978-1-78330-062-4 |url=https://books.google.com/books?id=awYUDgAAQBAJ&pg=PA14 |language=en |date=2016 }}
* {{cite web |last1=Stubenberg |first1=Leopold |last2=Wishon |first2=Donovan |title=Neutral Monism |url=https://plato.stanford.edu/entries/neutral-monism/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=27 March 2024 |date=2023 |archive-date=15 July 2018 |archive-url=https://web.archive.org/web/20180715152537/https://plato.stanford.edu/entries/neutral-monism/ |url-status=live }}
* {{cite web |last1=Studtmann |first1=Paul |title=Aristotle's Categories |url=https://plato.stanford.edu/entries/aristotle-categories/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=22 March 2024 |date=2024 |archive-date=6 July 2024 |archive-url=https://web.archive.org/web/20240706142224/https://plato.stanford.edu/entries/aristotle-categories/ |url-status=live }}
* {{cite book |last1=Svare |first1=Helge |title=Body and Practice in Kant |publisher=Springer Science & Business Media |isbn=978-1-4020-4118-1 |url=https://books.google.com/books?id=60MsUE3K2ekC&pg=PA15 |language=en |date=2006 |access-date=4 April 2024 |archive-date=2 April 2024 |archive-url=https://web.archive.org/web/20240402120906/https://books.google.com/books?id=60MsUE3K2ekC&pg=PA15 |url-status=live }}
* {{cite book |last1=Sweeney |first1=E. |title=Logic, Theology and Poetry in Boethius, Anselm, Abelard, and Alan of Lille: Words in the Absence of Things |date=2016 |publisher=Springer |isbn=978-1-137-06373-1 |url=https://books.google.com/books?id=orIYDAAAQBAJ |language=en |access-date=17 June 2023 |archive-date=22 June 2023 |archive-url=https://web.archive.org/web/20230622154205/https://books.google.com/books?id=orIYDAAAQBAJ |url-status=live }}
* {{cite book |last1=Tahko |first1=Tuomas E. |title=An Introduction to Metametaphysics |date=2015 |publisher=Cambridge University Press |isbn=978-1-107-07729-4}}
* {{cite web |last1=Tahko |first1=Tuomas E. |last2=Lowe |first2=E. Jonathan |title=Ontological Dependence |url=https://plato.stanford.edu/entries/dependence-ontological/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=2 July 2024 |date=2020 |archive-date=6 July 2024 |archive-url=https://web.archive.org/web/20240706142225/https://plato.stanford.edu/entries/dependence-ontological/ |url-status=live }}
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* {{cite book |last1=Tallant |first1=Jonathan |title=Metaphysics: An Introduction |publisher=Bloomsbury Academic |isbn=978-1-3500-0671-3 |edition=Second |date=2017 }}
* {{cite book |last1=Tambassi |first1=Timothy |title=The Philosophy of Geo-Ontologies |publisher=Springer |isbn=978-3-319-64033-4 |url=https://books.google.com/books?id=dtYtDwAAQBAJ&pg=PA6 |language=en |date=2017 }}
* {{cite book |last1=Tambassi |first1=Timothy |editor1-last=Tambassi |editor1-first=Timothy |title=Studies in the Ontology of E. J. Lowe |publisher=Taylor & Francis |isbn=978-3-86838-213-6 |chapter-url=https://books.google.com/books?id=JkCdEAAAQBAJ&pg=PA79 |language=en |chapter=The Riddle of Reality |date=2022 |access-date=2024-06-18 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706142227/https://books.google.com/books?id=JkCdEAAAQBAJ&pg=PA79#v=onepage&q&f=false |url-status=live }}
* {{cite web |last1=Textor |first1=Mark |title=States of Affairs |url=https://plato.stanford.edu/entries/states-of-affairs/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=3 July 2024 |date=2021 |archive-date=11 June 2018 |archive-url=https://web.archive.org/web/20180611161235/https://plato.stanford.edu/entries/states-of-affairs/ |url-status=live }}
* {{cite journal |last1=Thomasson |first1=Amie L. |title=Experimental Philosophy and the Methods of Ontology |journal=Monist |volume=95 |issue=2 |doi=10.5840/monist201295211 |date=2012 |pages=175–199 }}
* {{cite web |last1=Thomasson |first1=Amie |title=Categories |url=https://plato.stanford.edu/entries/categories/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=20 March 2024 |date=2022 |archive-date=8 October 2023 |archive-url=https://web.archive.org/web/20231008154635/https://plato.stanford.edu/entries/categories/ |url-status=live }}
* {{cite web |last1=Thompson |first1=Kirill |title=Zhu Xi |url=https://plato.stanford.edu/entries/zhu-xi/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=6 July 2024 |date=2021 }}
* {{cite book |last1=Thomson |first1=Ian |editor1-last=Dahlstrom |editor1-first=Daniel O. |title=Interpreting Heidegger: Critical Essays |publisher=Cambridge University Press |isbn=978-1-139-50042-5 |chapter-url=https://books.google.com/books?id=S1JS4X_1ORgC&pg=PA114 |language=en |chapter=Ontotheology |date=2011 |access-date=2024-06-29 |archive-date=2024-06-28 |archive-url=https://web.archive.org/web/20240628171430/https://books.google.com/books?id=S1JS4X_1ORgC&pg=PA114 |url-status=live }}
* {{cite book |last1=Tuomela |first1=Raimo |last2=Hakli |first2=Raul |last3=Mäkelä |first3=Pekka |title=Social Ontology in the Making |publisher=Walter de Gruyter GmbH & Co KG |isbn=978-3-11-061767-2 |chapter-url=https://books.google.com/books?id=P23cDwAAQBAJ&pg=PT9 |language=en |chapter=Social Ontology in the Making: An Introduction |date=2020 |access-date=2024-06-20 |archive-date=2024-06-18 |archive-url=https://web.archive.org/web/20240618170705/https://books.google.com/books?id=P23cDwAAQBAJ&pg=PT9 |url-status=live }}
* {{cite book |last1=Vaidya |first1=Anand Jayprakash |last2=Wallner |first2=Michale |editor1-last=Koslicki |editor1-first=Kathrin |editor2-last=Raven |editor2-first=Michael J. |title=The Routledge Handbook of Essence in Philosophy |publisher=Taylor & Francis |isbn=978-1-040-01688-6 |chapter-url=https://books.google.com/books?id=W34IEQAAQBAJ&pg=PA473 |language=en |chapter=Conferralism; |date=2024 |access-date=2024-07-03 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706142729/https://books.google.com/books?id=W34IEQAAQBAJ&pg=PA473#v=onepage&q&f=false |url-status=live }}
* {{cite journal |last1=Van Inwagen |first1=Peter |title=Relational Vs. Constituent Ontologies |journal=Philosophical Perspectives |volume=25 |issue=1 |doi=10.1111/j.1520-8583.2011.00221.x |date=2011 |pages=389–405 }}
* {{cite web |last1=Van Inwagen |first1=Peter |title=Existence |url=https://www.britannica.com/topic/existence |website=Encyclopædia Britannica |access-date=7 August 2023 |language=en |date=2023 |archive-date=29 June 2023 |archive-url=https://web.archive.org/web/20230629022444/https://www.britannica.com/topic/existence |url-status=live }}
* {{cite book |last1=Van Inwagen |first1=Peter |title=Metaphysics |publisher=Routledge |isbn=978-1-032-40916-0 |edition=5 |date=2024 }}
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* {{cite web |last1=Varzi |first1=Achille |title=Mereology |url=https://plato.stanford.edu/entries/mereology/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=25 March 2024 |date=2019 |archive-date=28 September 2020 |archive-url=https://web.archive.org/web/20200928232840/https://plato.stanford.edu/entries/mereology/ |url-status=live }}
* {{cite journal |last1=Vernekar |first1=Sanjyot D. Pai |title=Aurobindonian Ontology: Salient Peculiarities |journal=The Paideia Archive: Twentieth World Congress of Philosophy |doi=10.5840/wcp20-paideia199813282 |date=1998 |pages=81–86 |isbn=978-1-63435-051-8 }}
* {{cite book |last1=Vineberg |first1=Susan |editor1-last=Preyer |editor1-first=Gerhard |editor2-last=Peter |editor2-first=Georg |title=Philosophy of Mathematics: Set Theory, Measuring Theories, and Nominalism |publisher=Walter de Gruyter |isbn=978-3-11-032368-9 |chapter-url=https://books.google.com/books?id=0NJavSp-DbwC&pg=PA133 |language=en |chapter=Is Indispensability Still a Problem for Fictionalism? |date=2013 |access-date=2024-06-17 |archive-date=2024-06-17 |archive-url=https://web.archive.org/web/20240617092527/https://books.google.com/books?id=0NJavSp-DbwC&pg=PA133 |url-status=live }}
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* {{cite web |last1=Weir |first1=Alan |title=Formalism in the Philosophy of Mathematics |url=https://plato.stanford.edu/entries/formalism-mathematics/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=2 June 2024 |date=2024 |archive-date=1 February 2024 |archive-url=https://web.archive.org/web/20240201100923/https://plato.stanford.edu/entries/formalism-mathematics/ |url-status=live }}
* {{cite web |last1=Westacott |first1=Emrys |title=Moral Relativism |url=https://iep.utm.edu/moral-re/ |website=Internet Encyclopedia of Philosophy |access-date=19 December 2023 |archive-date=December 16, 2023 |archive-url=https://web.archive.org/web/20231216115535/https://iep.utm.edu/moral-re/ |url-status=live }}
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* {{cite web |last1=Williams |first1=Thomas |title=John Duns Scotus |url=https://plato.stanford.edu/entries/duns-scotus/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=25 June 2024 |date=2022 |archive-date=11 June 2017 |archive-url=https://web.archive.org/web/20170611075435/https://plato.stanford.edu/entries/duns-scotus/ |url-status=live }}
* {{cite book |last1=Wittgenstein |first1=Ludwig |translator-last1=Pears |translator-first1=David |translator-last2=McGuinness |translator-first2=Brian |title=Tractatus Logico-philosophicus |orig-date=1921 |publisher=Routledge |isbn=978-0-415-25562-2 |date=2001 }}
* {{cite book |last1=Woznicki |first1=Christopher Grzegorz |title=T. F. Torrance's Christological Anthropology: Discerning Humanity in Christ |publisher=Routledge |isbn=978-1-032-20134-4  |date=2022 }}
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* {{cite book |last1=Yao |first1=Zhihua |chapter=The Cognition of Nonexistent Objects: Five Yogācāra Arguments |editor-last1=Liu |editor-first1=Jeeloo |editor-last2=Berger |editor-first2=Douglas |title=Nothingness in Asian Philosophy |date=2014 |publisher=Routledge |isbn=978-1-317-68383-4 |chapter-url=https://books.google.com/books?id=NZjOAwAAQBAJ&pg=PA140 |language=en |access-date=1 September 2023 |archive-date=11 August 2023 |archive-url=https://web.archive.org/web/20230811074249/https://books.google.com/books?id=p5nOAwAAQBAJ&pg=PT150 |url-status=live }}
* {{cite journal |last1=Young |first1=Niki |title=Object, Reduction, and Emergence: An Object-Oriented View |journal=Open Philosophy |volume=4 |issue=1 |doi=10.1515/opphil-2020-0159 |date=2021 |pages=83–93 }}
* {{cite book |last1=Yu |first1=Liyang |title=A Developer's Guide to the Semantic Web |publisher=Springer |isbn=978-3-662-43796-4 |url=https://books.google.com/books?id=vcmoBQAAQBAJ&pg=PA357 |language=en |date=2014 |access-date=2024-06-29 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706142732/https://books.google.com/books?id=vcmoBQAAQBAJ&pg=PA357#v=onepage&q&f=false |url-status=live }}
* {{cite book |last1=Zhang |first1=Jiayan |title=One and Many: A Comparative Study of Plato's Philosophy and Daoism Represented by Ge Hong |publisher=University of Hawaii Press |isbn=978-0-8248-6118-6 |url=https://books.google.com/books?id=Vl4EEAAAQBAJ&pg=PA220 |language=en |date=2011 |access-date=2024-07-03 |archive-date=2024-07-06 |archive-url=https://web.archive.org/web/20240706142732/https://books.google.com/books?id=Vl4EEAAAQBAJ&pg=PA220#v=onepage&q&f=false |url-status=live }}
{{refend}}

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