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[[File:Aristotle, Metaphysics, Incunabulum.jpg|thumb|alt=Incunabulum showing a text of the beginning of Aristotle's ''Metaphysics'' at the center of the picture. A group of people in colorful robes stands above it and below it are animals on grass.|The beginning of [[Metaphysics (Aristotle)|Aristotle's ''Metaphysics'']], one of the foundational texts of the discipline]]

'''Metaphysics''' is the branch of [[philosophy]] that examines the basic structure of [[reality]]. It is traditionally seen as the study of mind-independent features of the world, but some theorists view it as an inquiry into the conceptual framework of human understanding. Some philosophers, including [[Aristotle]], designate metaphysics as '''first philosophy'''<!--boldface per WP:R#PLA--> to suggest that it is more fundamental than other forms of philosophical inquiry.

Metaphysics encompasses a wide range of general and abstract topics. It investigates the nature of [[existence]], the features all entities have in common, and their division into [[categories of being]]. An influential division is between [[particular]]s and [[Universal (metaphysics)|universals]]. Particulars are individual unique entities, like a specific apple. Universals are general features that different particulars have in common, like the color {{em|red}}. [[Modal metaphysics]] examines what it means for something to be possible or necessary. Metaphysicians also explore the [[Philosophy of space and time|concepts of space, time, and change]], and their connection to [[causality]] and the [[Scientific laws|laws of nature]]. Other topics include how [[mind–body problem|mind and matter are related]], whether everything in the world is [[Determinism|predetermined]], and whether there is [[free will]].

Metaphysicians use [[Philosophical methodology|various methods]] to conduct their inquiry. Traditionally, they rely on rational [[intuition]]s and [[abstract reasoning]] but have recently included [[Empirical evidence|empirical]] approaches associated with scientific theories. Due to the abstract nature of its topic, metaphysics has received criticisms questioning the reliability of its methods and the meaningfulness of its theories. Metaphysics is relevant to many fields of inquiry that often implicitly rely on metaphysical concepts and assumptions.

The [[History of metaphysics|roots of metaphysics]] lie in [[ancient period|antiquity]] with speculations about the nature and origin of the universe, like those found in the [[Upanishads]] in [[ancient India]], [[Daoism]] in [[ancient China]], and [[pre-Socratic philosophy]] in [[ancient Greece]]. During the subsequent [[medieval period]] in the West, discussions about the [[Problem of universals|nature of universals]] were influenced by the philosophies of [[Plato]] and Aristotle. The [[modern period]] saw the emergence of various comprehensive systems of metaphysics, many of which embraced [[idealism]]. In the 20th century, traditional metaphysics in general and idealism in particular faced various criticisms, which prompted new approaches to metaphysical inquiry.

== Definition ==
Metaphysics is the study of the most general features of [[reality]], including [[existence]], [[Subject and object (philosophy)|objects]] and their [[Property (philosophy)|properties]], possibility and necessity, [[space]] and [[time]], change, [[Causality|causation]], and the relation between [[matter]] and [[mind]]. It is one of the oldest branches of [[philosophy]].<ref>{{multiref | {{harvnb|Carroll|Markosian|2010|pp=1–3}} | {{harvnb|Koons|Pickavance|2015|pp=1–2}} | {{harvnb|McDaniel|2020|loc=§ 0.3 An Overview of Metaphysics and Other Areas of Philosophy}} | {{harvnb|Mumford|2012|loc=§ What Is an Introduction?}} }}</ref>{{efn|Philosophers engaged in metaphysics are called ''metaphysicians'' or ''metaphysicists''.<ref>{{multiref | {{harvnb|Mumford|2012|loc=§ 10 What Is Metaphysics?}} | {{harvnb|Carroll|Markosian|2010|p=2}} }}</ref> Outside the academic discourse, the term ''metaphysics'' is sometimes used in a different sense for the study of [[occult]] and [[paranormal]] phenomena, like metaphysical healing, [[Aura (paranormal)|auras]], and the [[Pyramid power|power of pyramids]].<ref>{{multiref | {{harvnb|Carroll|Markosian|2010|p=1}} | {{harvnb|Turner|1911|loc=[[:s:Catholic_Encyclopedia_(1913)/Metaphysics|I. The Name]]}} }}</ref>}}

The precise nature of metaphysics is disputed and its characterization has changed in the course of history. Some approaches see metaphysics as a unified field and give a wide-sweeping definition by understanding it as the study of "fundamental questions about the nature of reality" or as an inquiry into the [[essence]]s of things. Another approach doubts that the different areas of metaphysics share a set of underlying features and provides instead a fine-grained characterization by listing all the main topics investigated by metaphysicians.<ref>{{multiref | {{harvnb|Carroll|Markosian|2010|pp=1–4}} | {{harvnb|Loux|Crisp|2017|pp=1–2}} | {{harvnb|McDaniel|2020|loc=§ 0.3 An Overview of Metaphysics and Other Areas of Philosophy}} | {{harvnb|Mumford|2012|loc=§ 10 What Is Metaphysics?}} | {{harvnb|Ney|2014|pp=9–10}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=Lead Section, § 1. The Word 'Metaphysics' and the Concept of Metaphysics}} }}</ref> Some definitions are descriptive by providing an account of what metaphysicians do while others are normative and prescribe what metaphysicians ought to do.<ref>{{harvnb|Loux|Crisp|2017|p=2}}</ref>

Two historically influential definitions in [[ancient philosophy|ancient]] and [[medieval philosophy]] understand metaphysics as the science of the [[first cause]]s and as the study of being {{em|qua}} being, that is, the topic of what all beings have in common and to what fundamental categories they belong. In the modern period, the scope of metaphysics expanded to include topics such as the distinction between mind and body and [[free will]].<ref>{{multiref | {{harvnb|Loux|Crisp|2017|pp=1–4}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=Lead Section, § 1. The Word 'Metaphysics' and the Concept of Metaphysics}} }}</ref> Some philosophers follow [[Aristotle]] in describing metaphysics as "first philosophy", suggesting that it is the most basic inquiry upon which all other branches of philosophy depend in some way.<ref>{{multiref | {{harvnb|Koons|Pickavance|2015|pp=8–10}} | {{harvnb|Loux|Crisp|2017|pp=2–3}} }}</ref>{{efn|For example, the metaphysical problem of causation is relevant both to [[epistemology]], as a factor involved in perceptual knowledge, and [[ethics]], in regard to moral responsibility for the consequences caused by one's [[Action (philosophy)|actions]].<ref>{{harvnb|Koons|Pickavance|2015|pp=8–10}}</ref>}}

[[File:Kant gemaelde 1.jpg|thumb|alt=Oil painting showing Kant from the front against a dark background in a sitting position, leaning on a table with pens and ink and wearing brown formal dress|[[Immanuel Kant]] conceived metaphysics from the perspective of [[critical philosophy]] as the study of the principles underlying all human thought and experience.]]

Metaphysics is traditionally understood as a study of mind-independent features of reality. Starting with [[Immanuel Kant]]'s [[critical philosophy]], an alternative conception gained prominence that focuses on conceptual schemes rather than external reality. Kant distinguishes transcendent metaphysics, which aims to describe the objective features of reality beyond sense experience, from the [[Critical philosophy|critical perspective]] on metaphysics, which outlines the aspects and principles underlying all human thought and experience.<ref>{{multiref | {{harvnb|Loux|Crisp|2017|pp=1–2, 6–7}} | {{harvnb|Bengtson|2015|p=[https://books.google.com/books?id=4CnxCgAAQBAJ&pg=PA23 23]}} | {{harvnb|Wood|2009|p=[https://books.google.com/books?id=i7PG-Vk824UC&pg=PA354 354]}} }}</ref> Philosopher [[P. F. Strawson]] further explored the role of conceptual schemes, contrasting descriptive metaphysics, which articulates conceptual schemes commonly used to understand the world, with revisionary metaphysics, which aims to produce better conceptual schemes.<ref>{{multiref | {{harvnb|Heyndels|Bengtson|Mesel|2024|p=[https://books.google.com/books?id=_wvjEAAAQBAJ&pg=PA4 4]}} | {{harvnb|MacDonald|2008|p=[https://books.google.com/books?id=JjRG56XeyIcC&pg=PA18 18]}} }}</ref>

Metaphysics differs from the individual sciences by studying the most general and abstract aspects of reality. The individual sciences, by contrast, examine more specific and concrete features and restrict themselves to certain classes of entities, such as the focus on physical things in [[physics]], living entities in [[biology]], and cultures in [[anthropology]].<ref>{{multiref | {{harvnb|Mumford|2012|loc=§ 10 What Is Metaphysics?}} | {{harvnb|Ney|2014|p=xiii}} | {{harvnb|Tahko|2015|pp=206–207}} }}</ref> It is disputed to what extent this contrast is a strict dichotomy rather than a gradual continuum.<ref>{{harvnb|Tahko|2015|pp=203–205}}</ref>

===Etymology===
The word ''metaphysics'' has its origin in the ancient Greek words {{tlit|grc|[[Meta (prefix)|metá]]}} ({{lang|grc|[[wikt:μετά|μετά]]}}, meaning {{gloss|after}}, {{gloss|above}}, and {{gloss|beyond}}) and {{tlit|grc|phusiká}} ({{lang|grc|[[wikt:φυσικά|φυσικά]]}}), as a short form of {{tlit|grc|ta metá ta phusiká}}, meaning {{gloss|what comes after the physics}}. This is often interpreted to mean that metaphysics discusses topics that, due to their generality and comprehensiveness, lie beyond the realm of physics and its focus on empirical observation.<ref name=":0"/> Metaphysics may have received its name by a historical accident when [[Metaphysics (Aristotle)|Aristotle's book]] on this subject was published.<ref>{{multiref | {{harvnb|Hamlyn|2005|p=590}} | {{harvnb|Mumford|2012|loc=§ 10. What Is Metaphysics?}} | {{harvnb|Pols|1993|p=[https://books.google.com/books?id=sv84Gi7C9jgC&pg=PA203 203]}} | {{harvnb|Lowe|2013|p=[https://books.google.com/books?id=Las3AAAAQBAJ&pg=PA127 127]}} }}</ref> Aristotle did not use the term ''metaphysics'' but his editor (likely [[Andronicus of Rhodes]]) may have coined it for its title to indicate that this book should be studied after Aristotle's book published on [[Physics (Aristotle)|physics]]: literally {{gloss|after physics}}. The term entered the English language through the Latin word {{lang|la|[[wikt:metaphysica|metaphysica]]}}.<ref name=":0">{{multiref | {{harvnb|Hoad|1993|pp=291, 351}} | {{harvnb|Cohen|Reeve|2021|loc=Lead Section}} | {{harvnb|Carroll|Markosian|2010|pp=1–2}} | {{harvnb|Mumford|2012|loc=§ 10. What Is Metaphysics?}} | {{harvnb|Politis|2004|p=[https://books.google.com/books?id=d-GjOoZNnGsC&pg=PA1 1]}} }}</ref>

=== Branches ===
The nature of metaphysics can also be characterized in relation to its main branches. An influential division from early [[modern philosophy]] distinguishes between general and special or specific metaphysics.<ref>{{multiref | {{harvnb|Loux|Crisp|2017|pp=3–5, 10}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 1. The Word 'Metaphysics' and the Concept of Metaphysics}} | {{harvnb|Craig|1998}} | {{harvnb|Koons|Pickavance|2015|pp=1–2}} }}</ref> General metaphysics, also called ''[[ontology]]'',{{efn|The term ''[[ontology]]'' is sometimes also used as a synonym of metaphysics as a whole.<ref>{{harvnb|Hawley|2016|p=166}}</ref>}} takes the widest perspective and studies the most fundamental aspects of being. It investigates the features that all entities share and how entities can be divided into different [[categories of being|categories]]. Categories are the most general kinds, such as substance, property, [[Relation (philosophy)|relation]], and [[fact]].<ref>{{multiref | {{harvnb|Loux|Crisp|2017|pp=10–14}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 1. The Word 'Metaphysics' and the Concept of Metaphysics}} | {{harvnb|Campbell|2006|loc=The Categories Of Being}} }}</ref> Ontologists research which categories there are, how they depend on one another, and how they form a system of categories that provides a comprehensive classification of all entities.<ref>{{multiref | {{harvnb|Hofweber|2023|loc=§ 3. Ontology}} | {{harvnb|Campbell|2006|loc=The Categories Of Being}} | {{harvnb|Thomasson|2022|loc=Lead Section}} }}</ref>

Special metaphysics considers being from more narrow perspectives and is divided into subdisciplines based on the perspective they take. [[Metaphysical cosmology]] examines changeable things and investigates how they are connected to form a [[world]] as a totality extending through space and time.<ref name="Loux 2017 3–5, 10">{{multiref | {{harvnb|Loux|Crisp|2017|pp=3–5, 10}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 1. The Word 'Metaphysics' and the Concept of Metaphysics}} }}</ref> Rational psychology focuses on metaphysical foundations and problems concerning the mind, such as its relation to matter and the freedom of the will. Natural theology studies the divine and its role as the first cause.<ref name="Loux 2017 3–5, 10"/> The scope of special metaphysics overlaps with other philosophical disciplines, making it unclear whether a topic belongs to it or to areas like [[philosophy of mind]] and [[theology]].<ref>{{multiref | {{harvnb|Loux|Crisp|2017|pp=10–11}} | {{harvnb|Craig|1998|loc=§ 2. Specific Metaphysics}} }}</ref>

Starting in the second half of the 20th century, applied metaphysics was conceived as the area of [[applied philosophy]] examining the implications and uses of metaphysics, both within philosophy and other fields of inquiry. In areas like [[ethics]] and [[philosophy of religion]], it addresses topics like the ontological foundations of moral claims and religious doctrines.<ref>{{multiref | {{harvnb|Hawley|2016|pp=165–168}} | {{harvnb|Brumbaugh|1966|pp=[https://www.jstor.org/stable/20124133 647–648]}} }}</ref> Beyond philosophy, its applications include the use of ontologies in [[artificial intelligence]], [[economics]], and [[sociology]] to classify entities.<ref>{{harvnb|Hawley|2016|pp=168–169, 171–172}}</ref> In [[psychiatry]] and [[medicine]], it examines the metaphysical status of [[disease]]s.<ref>{{harvnb|Hawley|2016|p=174}}</ref>

{{anchor|Meta-metaphysics}}<!--'Metametaphysics' and 'Meta-metaphysics' redirect here-->
'''Meta-metaphysics'''<!--boldface per WP:R#PLA-->{{efn|Some philosophers use the term ''[[metaontology]]'' as a synonym while others characterize metaontology as a subfield of meta-metaphysics.<ref>{{harvnb|Tahko|2018|loc=Lead Section}}</ref>}} is the [[metatheory]] of metaphysics and investigates the nature and methods of metaphysics. It examines how metaphysics differs from other philosophical and scientific disciplines and assesses its relevance to them. Even though discussions of these topics have a long history in metaphysics, meta-metaphysics has only recently developed into a systematic field of inquiry.<ref>{{multiref | {{harvnb|McDaniel|2020|loc=§ 7 Meta-metaphysics}} | {{harvnb|Tahko|2018|loc=Lead Section}} }}</ref>

== Topics ==
=== Existence and categories of being ===
{{main|Existence|Theory of categories}}

Metaphysicians often regard existence or being as one of the most basic and general concepts.<ref>{{multiref | {{harvnb|Lowe|2005b|p=277}} | {{harvnb|White|2019|pp=135, 200}} | {{harvnb|Jubien|2004|pp=[https://books.google.com/books?id=uoCh8mpbZO4C&pg=PA47 47–48]}} }}</ref> To exist means to be part of [[reality]], distinguishing real entities from imaginary ones.<ref>{{multiref | {{harvnb|Lowe|2005b|p=277}} | {{harvnb|AHD staff|2022}} }}</ref> According to a traditionally influential view, existence is a property of properties: if an entity exists then its properties are instantiated.<ref>{{multiref |1={{harvnb|Casati|Fujikawa|loc=Lead Section, §1. Existence as a Second-Order Property and Its Relation to Quantification}} |2={{harvnb|Blackburn|2008|loc=[https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095804522;jsessionid=AEB41DBFF0B3EBCDCCB8A1E0DAFD4EB0 existence]}} }}</ref> A different position states that existence is a property of individuals, meaning that it is similar to other properties, such as shape or size.<ref>{{multiref |1={{harvnb|Casati|Fujikawa|loc=Lead Section, §2. Existence as a First-Order Property and Its Relation to Quantification}} |2={{harvnb|Blackburn|2008|loc=[https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095804522;jsessionid=AEB41DBFF0B3EBCDCCB8A1E0DAFD4EB0 existence]}} }}</ref> It is controversial whether all entities have this property. According to philosopher [[Alexius Meinong]], there are [[nonexistent objects]], including merely possible objects like [[Santa Claus]] and [[Pegasus]].<ref name="auto">{{multiref |1={{harvnb|Van Inwagen|2023}} |2={{harvnb|Nelson|2022|loc=Lead Section, §2. Meinongianism}} |3={{harvnb|Jubien|2004|p=[https://books.google.com/books?id=uoCh8mpbZO4C&pg=PA49 49]}} }}</ref>{{efn|According to Meinong, existence is not a synonym of being: all entities have being but not all entities have existence.<ref name="auto"/>}} A related question is whether existence is the same for all entities or whether there are different modes or degrees of existence.<ref>{{multiref |1={{harvnb|Casati|Fujikawa|loc=Lead Section, §3. How Many Ways of Being Existent?}} |2={{harvnb|McDaniel|2017|p=[https://books.google.com/books?id=8F0vDwAAQBAJ&pg=PT89 77]}} }}</ref> For instance, Plato held that [[Platonic forms]], which are perfect and immutable ideas, have a higher degree of existence than matter, which can only imperfectly reflect Platonic forms.<ref>{{multiref |1={{harvnb|Daly|2009|pp=227–228}} |2={{harvnb|Van Inwagen|2023}} }}</ref>{{efn|Although commonly labelled ''Plato's theory of forms'', there is some [[Socratic problem|scholarly disagreement]] about the extent to which this position belongs to [[Socrates]] rather than Plato.<ref>{{multiref | {{harvnb|Gerson|2002|p=[https://books.google.com/books?id=vbtbQk_A0YoC&pg=PA87 87]}} | {{harvnb|Dancy|2004|p=[https://books.google.com/books?id=WAoOQnoRa9gC&pg=PA11 11]}} }}</ref>}}

Another key concern in metaphysics is the division of entities into distinct groups based on underlying features they share. Theories of categories provide a system of the most fundamental kinds or the highest genera of being by establishing a comprehensive inventory of everything.<ref>{{multiref | {{harvnb|Thomasson|2022|loc=Lead Section}} | {{harvnb|Loux|Crisp|2017|pp=11–12}} | {{harvnb|Wardy|1998|loc=Lead Section}} }}</ref> One of the earliest theories of categories was proposed by Aristotle, who outlined a [[Categories_(Aristotle)#The_praedicamenta|system of 10 categories]]. He argued that [[Substance theory|substances]] (e.g., man and horse), are the most important category since all other categories like [[quantity]] (e.g., four), [[Quality (philosophy)|quality]] (e.g., white), and place (e.g., in Athens) are said of substances and depend on them.<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> Kant understood categories as fundamental principles underlying human understanding and developed a [[Category (Kant)|system of 12 categories]], divided into the 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> More recent theories of categories were proposed by [[Charles Sanders Peirce|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> Many philosophers rely on the contrast between [[Abstract and concrete|concrete and abstract objects]]. According to a common view, concrete objects, like rocks, trees, and human beings, exist in space and time, undergo changes, and impact each other as cause and effect. They contrast with abstract objects, like [[number]]s and [[Set (mathematics)|sets]], which do not exist in space and time, are immutable, and do not engage in causal relations.<ref>{{multiref | {{harvnb|Falguera|Martínez-Vidal|Rosen|2022|loc=Lead Section, § 1. Introduction, § 3.5 The Ways of Negation}} | {{harvnb|Erasmus|2018|p=[https://books.google.com/books?id=ze5FDwAAQBAJ&pg=PA93 93]}} }}</ref>

=== Particulars ===
[[Particular]]s are individual entities and include both concrete objects, like Aristotle, the Eiffel Tower, or a specific apple, and abstract objects, like the number 2 or a specific set in mathematics. They are unique, non-repeatable entities and contrast with [[Universal (metaphysics)|universals]], like the color red, which can at the same time exist in several places and characterize several particulars.<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> A widely held view is that particulars instantiate universals but are not themselves instantiated by something else, meaning that they exist in themselves while universals exist in something else. [[Substance theory|Substratum theory]], associated with [[John Locke]]'s philosophy, analyzes each particular as a substratum, also called ''bare particular'', together with various properties. The substratum confers individuality to the particular while the properties express its qualitative features or what it is like. This approach is rejected by [[Bundle theory|bundle theorists]]. Inspired by [[David Hume]]'s philosophy, they state that particulars are only bundles of properties without an underlying substratum. Some bundle theorists include in the bundle an individual essence, called ''[[haecceity]]'' following [[Scholasticism|scholastic]] terminology, to ensure that each bundle is unique. Another proposal for concrete particulars is that they are individuated by their space-time location.<ref>{{multiref | {{harvnb|Maurin|2019|loc=Lead Section}} | {{harvnb|Campbell|2006|loc=§ Particularity and Individuality}} | {{harvnb|Bigelow|1998|loc=Lead Section, § 3. Bundles of Properties}} | {{harvnb|Loux|Crisp|2017|pp=82–83}} }}</ref>

Concrete particulars encountered in everyday life, like rocks, tables, and organisms, are complex entities [[Composition (objects)|composed]] of various parts. For example, a table consists of a tabletop and legs, each of which is itself made up of countless particles. The relation between parts and wholes is studied by [[mereology]].<ref>{{multiref | {{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>{{efn|Mereological problems were discussed as early as ancient Greek philosophy.<ref>{{harvnb|Varzi|2019|loc=Lead Section}}</ref>}} The problem of the many is a philosophical question about the conditions under which several individual things compose a larger whole. For example, a cloud comprises many droplets without a clear boundary, raising the question of which droplets form part of the cloud. According to mereological universalists, every collection of entities forms a whole. This means that what seems to be a single cloud is an overlay of countless clouds, one for each cloud-like collection of water droplets. Mereological moderatists hold that certain conditions must be met for a group of entities to compose a whole, for example, that the entities touch one another. [[Mereological nihilism|Mereological nihilists]] reject the idea of wholes altogether, claiming that there are no clouds or tables but only particles that are arranged cloud-wise or table-wise.<ref>{{multiref | {{harvnb|Weatherson|2023|loc=Lead section, § 3. Overpopulation}} | {{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}} }}</ref> A related mereological problem is whether there are simple entities that have no parts, as [[Atomism|atomists]] claim, or whether everything can be endlessly subdivided into smaller parts, as continuum theorists contend.<ref>{{multiref | {{harvnb|Berryman|2022|loc=§ 2.6 Atomism and Particle Theories in Ancient Greek Sciences}} | {{harvnb|Varzi|2019|loc=§ 3.4 Atomism, Gunk, and Other Options}} }}</ref>

=== Universals ===
{{main|Universal (metaphysics)}}

Universals are general entities, encompassing both [[Property (philosophy)|properties]] and [[Relations (philosophy)|relations]], that express what particulars are like and how they resemble one another. They are repeatable, meaning that they are not limited to a unique existent but can be instantiated by different particulars at the same time. For example, the particulars [[Nelson Mandela]] and [[Mahatma Gandhi]] instantiate the universal {{em|humanity}}, similar to how a strawberry and a ruby instantiate the universal {{em|red}}.<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>

A topic discussed since ancient philosophy, the [[problem of universals]] consists in the challenge of characterizing the ontological status of universals.<ref>{{multiref | {{harvnb|MacLeod|Rubenstein|loc=Lead Section, § 1c. The Problem of Universals}} | {{harvnb|Rodriguez-Pereyra|2000|pp=255–256}} | {{harvnb|Loux|Crisp|2017|pp=17–19}} }}</ref> Realists argue that universals are real, mind-independent entities that exist in addition to particulars. According to [[Theory of forms|Platonic realists]], universals exist independently of particulars, which implies that the universal {{em|red}} would continue to exist even if there were no red things. A more [[Aristotelianism#Problem of universals|moderate form of realism]], inspired by Aristotle, states that universals depend on particulars, meaning that they are only real if they are instantiated. [[Nominalism|Nominalists]] reject the idea that universals exist in either form. For them, the world is composed exclusively of particulars. [[Conceptualism|Conceptualists]] offer an intermediate position, stating that universals exist, but only as [[concept]]s in the mind used to order experience by classifying entities.<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}} }}</ref>{{efn|The positions of nominalism and conceptualism were formulated in medieval philosophy.<ref>{{harvnb|Hancock|2006|pp=188–190}}</ref>}}

[[Natural kind|Natural]] and social kinds are often understood as special types of universals. Entities belonging to the same natural kind share certain fundamental features characteristic of the structure of the natural world. In this regard, natural kinds are not an artificially constructed classification but are discovered,{{efn|The classified entities do not have to occur naturally and can encompass man-made products, such as synthetic chemical substances.<ref>{{multiref | {{harvnb|Brzović|loc=Lead Section}} | {{harvnb|Bird|Tobin|2024|loc=Lead Section}} }}</ref>}} usually by the natural sciences, and include kinds like [[electrons]], [[H2O|{{chem2|H2O}}]], and tigers. [[Scientific realism|Scientific realists]] and anti-realists disagree about whether natural kinds exist.<ref>{{multiref | {{harvnb|Brzović|loc=Lead Section, § 3. Metaphysics of Natural Kinds}} | {{harvnb|Bird|Tobin|2024|loc=Lead Section, § 1.2 Natural Kind Realism}} | {{harvnb|Liston|loc=Lead Section}} }}</ref> Social kinds, like [[money]] and [[baseball]],<ref>{{multiref | {{harvnb|Ásta|2017|pp=[https://www.taylorfrancis.com/chapters/edit/10.4324/9781315768571-27/social-kinds-%C3%A1sta 290–291]}} | {{harvnb|Bird|Tobin|2024|loc=§ 2.4 Natural Kinds and Social Science}} }}</ref> are studied by [[social metaphysics]] and characterized as useful social constructions that, while not purely fictional, do not reflect the fundamental structure of mind-independent reality.<ref>{{multiref| {{harvnb|Ney|2014|pp=259–263}}| {{harvnb|Rea|2021|pp=185–186}}}}</ref>

=== Possibility and necessity ===
The concepts of possibility and necessity convey what can or must be the case, expressed in modal statements like "it is possible to find a cure for cancer" and "it is necessary that two plus two equals four". Modal metaphysics studies metaphysical problems surrounding possibility and necessity, for instance, why some modal statements are true while others are false.<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>{{efn|A further topic concerns different types of modality, such as the contrast between physical, metaphysical, and logical necessity based on whether the necessity has its source in the [[Scientific law|laws of nature]], the essences of things, or the laws of logic.<ref>{{multiref | {{harvnb|Hanna|2009|p=[https://books.google.com/books?id=ka9BhOL1ev8C&pg=PA196 196]}} | {{harvnb|Hale|2020|p=[https://books.google.com/books?id=OSvsDwAAQBAJ&pg=PA142 142]}} }}</ref>}} Some metaphysicians hold that modality is a fundamental aspect of reality, meaning that besides facts about what is the case, there are additional facts about what could or must be the case.<ref>{{multiref | {{harvnb|Goswick|2018|pp=97–98}} | {{harvnb|Wilsch|2017|pp=428–429, 446}} }}</ref> A different view argues that modal truths are not about an independent aspect of reality but can be reduced to non-modal characteristics, for example, to facts about what properties or linguistic descriptions are compatible with each other or to [[Fictionalism|fictional statements]].<ref>{{multiref | {{harvnb|Goswick|2018|pp=97–98}} | {{harvnb|Parent|loc=§ 3. Ersatzism, § 4. Fictionalism}} | {{harvnb|Wilsch|2017|pp=428–429}} }}</ref>

Borrowing a term from German philosopher [[Gottfried Wilhelm Leibniz]]'s [[theodicy]], many metaphysicians use the concept of [[possible world]]s to analyze the meaning and ontological ramifications of modal statements. A possible world is a complete and consistent way the totality of things could have been.<ref>{{multiref | {{harvnb|Menzel|2023|loc=Lead Section, § 1. Possible Worlds and Modal Logic}} | {{harvnb|Berto|Jago|2023|loc=Lead Section}} | {{harvnb|Pavel|1986|p=[https://books.google.com/books?id=OF7ZA54UpYYC&pg=PA50 50]}} | {{harvnb|Campbell|2006|loc=§ Possible Worlds}} }}</ref> For example, the [[dinosaurs]] were [[Cretaceous–Paleogene extinction event|wiped out]] in the actual world but there are possible worlds in which they are still alive.<ref>{{harvnb|Nuttall|2013|p=[https://books.google.com/books?id=luc-Hf_bEOIC&pg=PT135 135]}}</ref> According to possible world semantics, a statement is possibly true if it is true in at least one possible world, whereas it 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> [[Modal realism|Modal realists]] argue that possible worlds exist as concrete entities in the same sense as the actual world, with the main difference being that the actual world is the world we live in while other possible worlds are inhabited by [[Counterpart theory|counterparts]]. This view is controversial and various alternatives have been suggested, for example, that possible worlds only exist as abstract objects or are similar to stories told in works of [[fiction]].<ref>{{multiref | {{harvnb|Parent|loc=Lead Section, § 2. Lewis' Realism, § 3. Ersatzism, § 4. Fictionalism}} | {{harvnb|Menzel|2023|loc=Lead Section, § 2. Three Philosophical Conceptions of Possible Worlds}} | {{harvnb|Campbell|2006|loc=§ Modal Realism}} }}</ref>

=== Space, time, and change ===
{{main|Philosophy of space and time}}

[[Space]] and [[time]] are dimensions that entities occupy. Spacetime realists state that space and time are fundamental aspects of reality and exist independently of the human mind. Spacetime idealists, by contrast, hold that space and time are constructs of the human mind, created to organize and make sense of reality.<ref>{{multiref | {{harvnb|Dainton|2010|pp=[https://www.cambridge.org/core/books/abs/time-and-space/spatial-antirealism/CE284C8D3088AF598998951618D4867D 245–246]}} | {{harvnb|Janiak|2022|loc=§ 4.2 Absolute/Relational Vs. Real/Ideal}} | {{harvnb|Pelczar|2015|p=[https://books.google.com/books?id=tkjTBgAAQBAJ&pg=PA115 115]}} }}</ref> Spacetime absolutism or substantivalism understands spacetime as a distinct object, with some metaphysicians conceptualizing it as a container that holds all other entities within it. [[Relationalism#Relationalism (theory of space and time)|Spacetime relationism]] sees spacetime not as an object but as a network of relations between objects, such as the spatial relation of {{em|being next to}} and the temporal relation of {{em|coming before}}.<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>

In the metaphysics of time, an important contrast is between the [[A series and B series|A-series and the B-series]]. According to the A-series theory, the [[flow of time]] is real, meaning that events are categorized into the past, present, and future. The present continually moves forward in time and events that are in the present now will eventually change their status and lie in the past. From the perspective of the B-series theory, time is static, and events are ordered by the temporal relations earlier-than and later-than without any essential difference between past, present, and future.<ref>{{multiref | {{harvnb|Dyke|2002|p=[https://books.google.com/books?id=IxIlqbSWg4gC&pg=PA138 138]}} | {{harvnb|Koons|Pickavance|2015|pp=182–185}} | {{harvnb|Carroll|Markosian|2010|pp=160–161}} }}</ref> [[Eternalism (philosophy of time)|Eternalism]] holds that past, present, and future are equally real, whereas [[Presentism (philosophy of time)|presentism]] asserts that only entities in the present exist.<ref>{{multiref | {{harvnb|Carroll|Markosian|2010|pp=179–181}} | {{harvnb|Loux|Crisp|2017|pp=206, 214–215}} | {{harvnb|Romero|2018|p=[https://books.google.com/books?id=5wJ2DwAAQBAJ&pg=PA135 135]}} }}</ref>

Material objects persist through time and change in the process, like a tree that grows or loses leaves.<ref>{{multiref | {{harvnb|Miller|2018|loc=Lead Section}} | {{harvnb|Costa|loc=Lead Section}} | {{harvnb|Simons|2013|p=[https://books.google.com/books?id=ql27m77IveQC&pg=PA166 166]}} }}</ref> The main ways of conceptualizing persistence through time are [[endurantism]] and [[perdurantism]]. According to endurantism, material objects are three-dimensional entities that are wholly present at each moment. As they change, they gain or lose properties but otherwise remain the same. Perdurantists see material objects as four-dimensional entities that extend through time and are made up of different [[temporal parts]]. At each moment, only one part of the object is present, not the object as a whole. Change means that an earlier part is qualitatively different from a later part. For example, when a banana ripens, there is an unripe part followed by a ripe part.<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>

=== Causality ===
{{main|Causality}}

Causality is the relation between cause and effect whereby one entity produces or alters another entity.<ref>{{multiref | {{harvnb|Carroll|Markosian|2010|pp=20–22}} | {{harvnb|Tallant|2017|pp=218–219}} }}</ref> For instance, if a person bumps a glass and spills its contents then the bump is the cause and the spill is the effect.<ref>{{harvnb|Carroll|Markosian|2010|p=20}}</ref> Besides the single-case causation between particulars in this example, there is also general-case causation expressed in statements such as "smoking causes cancer".<ref>{{multiref | {{harvnb|Carroll|Markosian|2010|pp=21–22}} | {{harvnb|Williamson|2012|p=[https://books.google.com/books?id=yWWEIvNgUQ4C&pg=PA186 186]}} }}</ref> The term [[agent causation]] is used when people and their actions cause something.<ref>{{multiref | {{harvnb|Ney|2014|pp=219, 252–253}} | {{harvnb|Tallant|2017|pp=233–234}} }}</ref> Causation is usually interpreted deterministically, meaning that a cause always brings about its effect. However, some philosophers such as [[G. E. M. Anscombe]] have provided counterexamples to this idea.<ref>{{multiref|{{harvnb|Wiland|Driver|2022|loc=§ 3. Metaphysics}}|{{harvnb|Van Miltenburg|2022|pp=1, 6}}}}</ref> Such counterexamples have inspired the development of [[Probabilistic causation|probabilistic theories]], which claim that the cause merely increases the probability that the effect occurs. This view can explain that smoking causes cancer even though this does not happen in every single case.<ref>{{multiref | {{harvnb|Ney|2014|pp=228–231}} | {{harvnb|Williamson|2012|pp=[https://books.google.com/books?id=yWWEIvNgUQ4C&pg=PA185 185–186]}} }}</ref>

The [[Humeanism#Causality and necessity|regularity theory of causation]], inspired by [[David Hume]]'s philosophy, states that causation is nothing but a [[constant conjunction]] in which the mind apprehends that one phenomenon, like putting one's hand in a fire, is always followed by another phenomenon, like a feeling of pain.<ref>{{multiref | {{harvnb|Lorkowski|loc=Lead Section, § 2. Necessary Connections and Hume’s Two Definitions, § 4. Causal Reductionism}} | {{harvnb|Carroll|Markosian|2010|pp=24–25}} | {{harvnb|Tallant|2017|pp=220–221}} }}</ref> According to nomic regularity theories, regularities manifest as [[Scientific law|laws of nature]] studied by science.<ref>{{harvnb|Ney|2014|pp=223–224}}</ref> [[Counterfactual conditional|Counterfactual]] theories focus not on regularities but on how effects depend on their causes. They state that effects owe their existence to the cause and would not occur without them.<ref>{{multiref | {{harvnb|Carroll|Markosian|2010|p=26}} | {{harvnb|Tallant|2017|pp=221–222}} | {{harvnb|Ney|2014|pp=224–225}} }}</ref> According to primitivism, causation is a basic concept that cannot be analyzed in terms of non-causal concepts, such as regularities or dependence relations. One form of primitivism identifies causal powers inherent in entities as the underlying mechanism.<ref>{{multiref | {{harvnb|Ney|2014|pp=231–232}} | {{harvnb|Mumford|2009|pp=94–95}} | {{harvnb|Mumford|Anjum|2013}} | {{harvnb|Koons|Pickavance|2015|pp=63–64}} }}</ref> Eliminativists reject the above theories by holding that there is no causation.<ref>{{harvnb|Tallant|2017|pp=231–232}}</ref>

=== Mind and free will ===
{{main|Mind|Free will}}

[[File:Dualism-vs-Monism.png|thumb|right|upright=1.3|alt=Diagram of approaches to the mind–body problem. It shows dualism in the form of Cartesian dualism on the left side. It presents monism in the forms of physicalism, idealism, and neutral monism on the right side.|Different approaches toward resolving the mind–body problem<ref>{{harvnb|Kind|Stoljar|2023|loc=[https://books.google.com/books?id=_VC_EAAAQBAJ&pg=PT19 § Introduction]}}</ref>]]

Mind encompasses phenomena like [[thinking]], [[perceiving]], [[feeling]], and [[desiring]] as well as the underlying faculties responsible for these phenomena.<ref>{{harvnb|Morton|2005|p=[https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1608?rskey=jqUtkA&result=1601 603]}}</ref> The [[mind–body problem]] is the challenge of clarifying the relation between physical and mental phenomena. According to [[Cartesian dualism]], minds and bodies are distinct substances. They causally interact with each other in various ways but can, at least in principle, exist on their own.<ref>{{multiref | {{harvnb|McLaughlin|1999|pp=684–685}} | {{harvnb|Kim|2005|p=608}} }}</ref> This view is rejected by [[Monism|monists]], who argue that reality is made up of only one kind. According to metaphysical [[idealism]], everything is mental or dependent on the mind, including physical objects, which may be understood as ideas or perceptions of conscious minds.{{efn|There are other forms of idealism that assert slightly different positions, such as [[transcendental idealism]] and [[absolute idealism]].<ref>{{multiref | {{harvnb|Alston|2018|p=[https://books.google.com/books?id=4JNlDwAAQBAJ&pg=PA97 97]}} | {{harvnb|Guyer|Horstmann|2023|loc=§ 1. Introduction}} }}</ref>}} Materialists, by contrast, state that all reality is at its core material. Some deny that mind exists but the more common approach is to explain mind in terms of certain aspects of matter, such as brain states, behavioral [[disposition]]s, or functional roles.<ref>{{multiref | {{harvnb|McLaughlin|1999|pp=685–691}} | {{harvnb|Kim|2005|p=608}} | {{harvnb|Ramsey|2022|loc=Lead Section}} | {{harvnb|Pradhan|2020|p=[https://books.google.com/books?id=tSz7DwAAQBAJ&pg=PA4 4]}} }}</ref> [[Neutral monism|Neutral monists]] argue that reality is fundamentally neither material nor mental and suggest that matter and mind are both derivative phenomena.<ref>{{multiref | {{harvnb|Stubenberg|Wishon|2023|loc=Lead Section; § 1.3 Mind and Matter Revisited}} | {{harvnb|Griffin|1998}} }}</ref> A key aspect of the mind–body problem is the [[hard problem of consciousness]] or how to explain that physical systems like brains can produce phenomenal consciousness.<ref>{{harvnb|Weisberg|loc=Lead Section, § 1. Stating the Problem}}</ref>

The status of free will as the ability of a person to choose their [[Action (philosophy)|actions]] is a central aspect of the mind–body problem.<ref>{{multiref | {{harvnb|Timpe|loc=Lead Section}} | {{harvnb|Olson|2001|loc=[https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/mind-body-problem Mind–Body Problem]}} | {{harvnb|Armstrong|2018|p=[https://books.google.com/books?id=uf7EDwAAQBAJ&pg=PA94 94]}} }}</ref> Metaphysicians are interested in the relation between free will and [[causal determinism]]{{em dash}}the view that everything in the universe, including human behavior, is determined by preceding events and laws of nature. It is controversial whether causal determinism is true, and, if so, whether this would imply that there is no free will. According to [[incompatibilism]], free will cannot exist in a deterministic world since there is no true choice or control if everything is determined.{{efn|For example, the [[consequence argument]] by [[Peter van Inwagen]] says that people have no power over the future if everything is determined by the past together with the laws of nature.<ref>{{multiref | {{harvnb|Vihvelin|2022|loc=§ 5. Choice and the Consequence Argument}} | {{harvnb|Kane|2011|p=[https://books.google.com/books?id=bOdoAgAAQBAJ&pg=PA10 10]}} }}</ref>}} [[Hard determinists]] infer from this that there is no free will, whereas [[Libertarianism (metaphysics)|libertarians]] conclude that determinism must be false. [[Compatibilists]] offer a third perspective, arguing that determinism and free will do not exclude each other, for instance, because a person can still act in tune with their motivation and choices even if they are determined by other forces. Free will plays a key role in ethics regarding the [[moral responsibility]] people have for what they do.<ref>{{multiref | {{harvnb|O’Connor|Franklin|2022|loc=Lead Section, § 2. The Nature of Free Will}} | {{harvnb|Timpe|loc=Lead Section, § 1. Free Will, Free Action and Moral Responsibility, § 3. Free Will and Determinism}} | {{harvnb|Armstrong|2018|p=[https://books.google.com/books?id=uf7EDwAAQBAJ&pg=PA94 94]}} }}</ref>

=== Others ===
[[Identity (philosophy)|Identity]] is a relation that every entity has to itself as a form of sameness. It refers to numerical identity when the same entity is involved, as in the statement "the [[Phosphorus (morning star)|morning star]] is the [[Hesperus|evening star]]" (both are the planet [[Venus]]). In a slightly different sense, it encompasses qualitative identity, also called ''exact similarity'' and ''indiscernibility'', which occurs when two distinct entities are exactly alike, such as perfect identical twins.<ref>{{multiref | {{harvnb|Kirwan|2005|pp=417–418}} | {{harvnb|Noonan|Curtis|2022|loc=Lead Section}} }}</ref> The principle of the indiscernibility of identicals is widely accepted and holds that numerically identical entities exactly resemble one another. The converse principle, known as the [[identity of indiscernibles]] or Leibniz's Law, is more controversial and states that two entities are numerically identical if they exactly resemble one another.<ref>{{multiref | {{harvnb|Sleigh|2005|p=418}} | {{harvnb|Kirwan|2005|pp=417–418}} | {{harvnb|Noonan|Curtis|2022|loc=§ 2. The Logic of Identity}} }}</ref> Another distinction is between synchronic and diachronic identity. Synchronic identity relates an entity to itself at the same time, whereas diachronic identity is about the same entity at different times, as in statements like "the table I bought last year is the same as the table in my dining room now".<ref>{{multiref | {{harvnb|Gallois|2016|loc=§ 2.1 Diachronic and Synchronic Identity}} | {{harvnb|Noonan|Curtis|2022|loc=Lead Section, § 5. Identity Over Time}} }}</ref> [[Personal identity]] is a related topic in metaphysics that uses the term ''identity'' in a slightly different sense and concerns questions like what [[personhood]] is or what makes someone a person.<ref>{{multiref | {{harvnb|Noonan|Curtis|2022|loc=Lead Section}} | {{harvnb|Olson|2023|loc=Lead Section, § 1. The Problems of Personal Identity}} | {{harvnb|Korfmacher}} }}</ref>

Various contemporary metaphysicians rely on the concepts of [[truth]], [[truth-bearer]], and [[Truthmaker theory|truthmaker]] to conduct their inquiry.<ref>{{multiref | {{harvnb|Tallant|2017|pp=1–4}} | {{harvnb|Koons|Pickavance|2015|pp=15–17}} }}</ref> Truth is a property of being in accord with reality. Truth-bearers are entities that can be true or false, such as linguistic statements and mental representations. A truthmaker of a statement is the entity whose existence makes the statement true.<ref>{{multiref | {{harvnb|Lowe|2005a|p=926}} | {{harvnb|Tallant|2017|pp=1–4}} | {{harvnb|Koons|Pickavance|2015|pp=15–17}} | {{harvnb|Asay|2020|p=[https://books.google.com/books?id=nRXeDwAAQBAJ&pg=PA11 11]}} | {{harvnb|MacBride|2022}} }}</ref> For example, the fact that a tomato exists and that it is red acts as a truthmaker for the statement "a tomato is red".<ref>{{multiref | {{harvnb|Rodriguez-Pereyra|2006|pp=191–192}} | {{harvnb|Beebee|Dodd|2005|pp=[https://books.google.com/books?id=l24TDAAAQBAJ&pg=PA2 2–3]}} | {{harvnb|Tallant|2017|p=1}} }}</ref> Based on this observation, it is possible to pursue metaphysical research by asking what the truthmakers of statements are, with different areas of metaphysics being dedicated to different types of statements. According to this view, modal metaphysics asks what makes statements about what is possible and necessary true while the metaphysics of time is interested in the truthmakers of temporal statements about the past, present, and future.<ref>{{multiref | {{harvnb|Tallant|2017|pp=1–4, 163–165}} | {{harvnb|Koons|Pickavance|2015|pp=15–17, 154}} | {{harvnb|Meinertsen|2018|pp=[https://books.google.com/books?id=8HiQDwAAQBAJ&pg=PA21 21–22]}} }}</ref> A closely related topic concerns the nature of truth. Theories of truth aim to determine this nature and include [[Correspondence theory of truth|correspondence]], [[Coherence theory of truth|coherence]], [[Pragmatic theory of truth|pragmatic]], [[Semantic theory of truth|semantic]], and [[Deflationary theory of truth|deflationary theories]].<ref>{{multiref | {{harvnb|Dowden|Swartz|loc=Lead section}} | {{harvnb|Engel|2014|pp=12, 34–35, 47}} }}</ref>

== Methodology ==
Metaphysicians employ a variety of [[Philosophical methodology|methods]] to develop metaphysical theories and formulate arguments for and against them.<ref>{{multiref | {{harvnb|Loux|Crisp|2017|pp=xi, 2}} | {{harvnb|Koons|Pickavance|2015|pp=2–3}} }}</ref> Traditionally, ''[[A priori and a posteriori|a priori]]'' methods have been the dominant approach. They rely on rational [[intuition]] and abstract reasoning from general principles rather than sensory [[experience]]. ''A posteriori'' approaches, by contrast, ground metaphysical theories in [[empirical observation]]s and scientific theories.<ref>{{multiref | {{harvnb|Koons|Pickavance|2015|pp=2–3}} | {{harvnb|Mumford|2012|loc=§ 10. What Is Metaphysics?}} | {{harvnb|Tahko|2015|pp=151–152}} | {{harvnb|Jaksland|2023|pp=198–199}} }}</ref> Some metaphysicians incorporate perspectives from fields such as [[physics]], [[psychology]], [[linguistics]], and [[history]] into their inquiry.<ref>{{harvnb|Koons|Pickavance|2015|pp=2–3}}</ref> The two approaches are not mutually exclusive: it is possible to combine elements from both.<ref>{{harvnb|Tahko|2015|pp=151–152, 172–173}}</ref> The method a metaphysician chooses often depends on their understanding of the nature of metaphysics, for example, whether they see it as an inquiry into the mind-independent structure of reality, as [[Metaphysical realism|metaphysical realists]] claim, or the principles underlying thought and experience, as some [[Metaphysical anti-realism|metaphysical anti-realists]] contend.<ref>{{multiref | {{harvnb|Mumford|2012|loc=§ 10. What Is Metaphysics?}} | {{harvnb|Koons|Pickavance|2015|pp=2–3}} | {{harvnb|Effingham|Beebee|Goff|2010|p=[https://books.google.com/books?id=BBKsAgAAQBAJ&pg=PA123 123]}} | {{harvnb|Khlentzos|2021|loc=Lead Section, § 3. The Anti-Realist Challenges to Metaphysical Realism}} }}</ref>

''A priori'' approaches often rely on intuitions{{em dash}}non-inferential impressions about the correctness of specific claims or general principles.<ref>{{multiref | {{harvnb|Daly|2015|pp=[https://link.springer.com/chapter/10.1057/9781137344557_1 11–12]|loc=Introduction and Historical Overview}} | {{harvnb|Duignan|2009}} | {{harvnb|Tahko|2015|pp=177–180}}}}</ref>{{efn|The term ''intuition'' has a variety of other meanings in philosophy. It can refer to a simple opinion, a disposition to belief, what seems to be the case, or a relation between the mind and abstract objects.<ref>{{multiref | {{harvnb|Pust|2019|loc=§ 1. The Nature of Intuitions}} | {{harvnb|Lacey|2005|p=[https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1255 442]}} }}</ref> The concept plays a central role in the philosophy of [[Immanuel Kant]], who understands intuitions as conscious, objective representations closely associated with the sense of space and time.<ref>{{multiref | {{harvnb|Janiak|2022|loc=§ 2.2 Kant's Understanding of Representation}} | {{harvnb|Lacey|2005|p=[https://www.oxfordreference.com/display/10.1093/acref/9780199264797.001.0001/acref-9780199264797-e-1255 442]}} }}</ref>}} For example, arguments for the [[A-theory of time]], which states that time flows from the past through the present and into the future, often rely on pre-theoretical intuitions associated with the sense of the passage of time.<ref>{{harvnb|Tahko|2015|pp=188–190}}</ref> Some approaches use intuitions to establish a small set of [[self-evident]] fundamental principles, known as [[axiom]]s, and employ [[deductive reasoning]] to build complex metaphysical systems by drawing conclusions from these axioms.<ref>{{harvnb|Goldenbaum|loc=Lead Section, § 1. The Geometrical Method}}</ref> Intuition-based approaches can be combined with [[thought experiments]], which help evoke and clarify intuitions by linking them to imagined situations. They use [[counterfactual thinking]] to assess the possible consequences of these situations.<ref>{{multiref | {{harvnb|Tahko|2015|pp=177–178}} | {{harvnb|Brown|Fehige|2019|loc=Lead Section}} | {{harvnb|Goffi|Roux|2011|pp=[https://philpapers.org/rec/GOFOTV 165, 168–169]}} | {{harvnb|Eder|Lawler|Van Riel|2020|pp=915–916}} }}</ref> For example, to explore the relation between matter and consciousness, some theorists compare humans to [[philosophical zombies]]{{em dash}}hypothetical creatures identical to humans but without [[Consciousness|conscious experience]].<ref>{{harvnb|Kirk|2023|loc=Lead Section, § 2. Zombies and Physicalism}}</ref> A related method relies on commonly accepted beliefs instead of intuitions to formulate arguments and theories. The [[Common sense|common-sense]] approach is often used to criticize metaphysical theories that deviate significantly from how the average person thinks about an issue. For example, common-sense philosophers have argued that [[mereological nihilism]] is false since it implies that commonly accepted things, like tables, do not exist.<ref>{{multiref | {{harvnb|Lawson|2020|pp=185–186}} | {{harvnb|Jaksland|2023|pp=198–199}} }}</ref>

[[Conceptual analysis]], a method particularly prominent in [[analytic philosophy]], aims to decompose metaphysical concepts into component parts to clarify their meaning and identify essential relations.<ref>{{multiref | {{harvnb|Jackson|1998|pp=28–30}} | {{harvnb|Eder|Lawler|Van Riel|2020|p=915}} | {{harvnb|Shaffer|2015|pp=[https://www.jstor.org/stable/26602327 555–556]}} | {{harvnb|Audi|2006|loc=[https://www.encyclopedia.com/philosophy-and-religion/philosophy/philosophy-terms-and-concepts/philosophy § Philosophical Methods]}} }}</ref> In [[Phenomenology (philosophy)|phenomenology]], the method of [[eidetic variation]] is used to investigate essential structures underlying [[Phenomenon|phenomena]]. This method involves imagining an object and varying its features to determine which ones are essential and cannot be changed.<ref>{{multiref | {{harvnb|Drummond|2022|p=[https://books.google.com/books?id=VQ9hEAAAQBAJ&pg=PA75 75]}} | {{harvnb|Lohmar|2010|p=[https://books.google.com/books?id=rsqdCfBCL1MC&pg=PA83 83]}} }}</ref> The [[Transcendental arguments|transcendental]] method is a further approach and examines the metaphysical structure of reality by observing what entities there are and studying the [[Condition of possibility|conditions of possibility]] without which these entities could not exist.<ref>{{multiref | {{harvnb|Pihlström|2009|pp=[https://books.google.com/books?id=srGLpb7pWdkC&pg=PA60 60–61]}} | {{harvnb|Stern|Cheng|2023|loc=Lead Section}} }}</ref>

Some approaches give less importance to ''a priori'' reasoning and view metaphysics as a practice continuous with the empirical sciences that generalizes their insights while making their underlying assumptions explicit. This approach is known as ''naturalized metaphysics'' and is closely associated with the work of [[Willard Van Orman Quine]].<ref>{{multiref | {{harvnb|Ney|2014|pp=30–31}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} | {{harvnb|Jaksland|2023|pp=198–199}} }}</ref> He relies on the idea that true sentences from the sciences and other fields have [[ontological commitments]], that is, they imply that certain entities exist.<ref>{{multiref | {{harvnb|Ney|2014|pp=37–38, 40}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} }}</ref> For example, if the sentence "some electrons are bonded to protons" is true then it can be used to justify that electrons and protons exist.<ref>{{harvnb|Ney|2014|p=41}}</ref> Quine used this insight to argue that one can learn about metaphysics by closely analyzing{{efn|Quine's method of analysis relies on [[logic translation]] to [[first-order logic]] in order to express claims as precisely as possible while relying [[existential quantifier]]s to identify their ontological commitments.<ref>{{harvnb|Ney|2014|pp=40–41}}</ref>}} scientific claims to understand what kind of metaphysical picture of the world they presuppose.<ref>{{multiref | {{harvnb|Ney|2014|pp=40–43}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} }}</ref>

In addition to methods of conducting metaphysical inquiry, there are various methodological principles used to decide between competing theories by comparing their theoretical virtues. [[Ockham's Razor]] is a well-known principle that gives preference to simple theories, in particular, those that assume that few entities exist. Other principles consider [[explanatory power]], theoretical usefulness, and proximity to established beliefs.<ref>{{multiref | {{harvnb|McDaniel|2020|pp=[https://books.google.com/books?id=3tDaDwAAQBAJ&pg=PA217 217–221]}} | {{harvnb|Ney|2014|pp=48–49}} | {{harvnb|Mumford|2012|loc=§ 10. What Is Metaphysics?}} | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 4. The Methodology of Metaphysics}} | {{harvnb|Koons|Pickavance|2015|pp=2–3}} }}</ref>

== Criticism <!--'Antimetaphysicalism' and 'Anti-metaphysicalism' redirect here-->==
[[File:Allan Ramsay - David Hume, 1711 - 1776. Historian and philosopher - Google Art Project.jpg|thumb|alt=Oil painting showing David Hume from the front against a dark background, dressed in a red coat with gold embroidery, his left arm resting on a surface|[[David Hume]] criticizes metaphysicians for trying to gain knowledge outside the field of sensory experience.]]

Despite its status as one of the main branches of philosophy, metaphysics has received numerous criticisms questioning its legitimacy as a field of inquiry.<ref>{{multiref | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 5. Is Metaphysics Possible?}} | {{harvnb|Manley|2009|pp=1–2}} }}</ref> One criticism argues that metaphysical inquiry is impossible because humans lack the cognitive capacities needed to access the ultimate nature of reality.<ref>{{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 5. Is Metaphysics Possible?}}</ref> This line of thought leads to [[skepticism]] about the possibility of metaphysical knowledge. Empiricists often follow this idea, like Hume, who asserts that there is no good [[Knowledge#Sources|source of metaphysical knowledge]] since metaphysics lies outside the field of [[Empirical evidence|empirical knowledge]] and relies on dubious intuitions about the realm beyond sensory experience. Arguing that the mind actively structures experience, [[Critique of Pure Reason|Kant criticizes traditional metaphysics]] for its attempt to gain insight into the mind-independent nature of reality. He asserts that knowledge is limited to the realm of possible experience, meaning that humans are not able to decide questions like [[Kant's antinomies#The first antinomy (of space and time)|whether the world has a beginning in time or is infinite]]. A related argument favoring the unreliability of metaphysical theorizing points to the deep and lasting [[Disagreements (epistemology)|disagreements]] about metaphysical issues, suggesting a lack of overall progress.<ref>{{multiref | {{harvnb|Rea|2021|pp=210–212}} | {{harvnb|Carroll|Markosian|2010|pp=16–17}} | {{harvnb|Koons|Pickavance|2015|pp=4–5}} | {{harvnb|Willaschek|2018|p=[https://books.google.com/books?id=wmjtDwAAQBAJ&pg=PA43 43]}} | {{harvnb|McCormick|loc=Lead section, § 6. Kant's Dialectic }} }}</ref>

Another criticism holds that the problem lies not with human cognitive abilities but with metaphysical statements themselves, which some claim are neither true nor false but [[Meaning (philosophy)|meaningless]]. According to [[Logical positivism|logical positivists]], for instance, the meaning of a statement is given by the procedure used to [[Verificationism|verify]] it, usually through the [[observations]] that would confirm it. Based on this controversial assumption, they argue that metaphysical statements are meaningless since they make no testable predictions about experience.<ref>{{multiref | {{harvnb|Van Inwagen|Sullivan|Bernstein|2023|loc=§ 5. Is Metaphysics Possible?}} | {{harvnb|Manley|2009|p=4}} | {{harvnb|Rea|2021|pp=212–215}} | {{harvnb|Koons|Pickavance|2015|p=5}} }}</ref>

{{anchor|Ontological deflationism}}
A slightly weaker position allows metaphysical statements to have meaning while holding that metaphysical disagreements are merely verbal disputes about different ways to describe the world. According to this view, the disagreement in the metaphysics of composition about whether there are tables or only particles arranged table-wise is a trivial debate about linguistic preferences without any substantive consequences for the nature of reality.<ref>{{multiref | {{harvnb|Manley|2009|pp=1–4}} | {{harvnb|Rea|2021|pp=213–215}} | {{harvnb|Tahko|2015|pp=71–72}} }}</ref> The position that metaphysical disputes have no meaning or no significant point is called ''metaphysical'' or ''ontological deflationism''.<ref>{{multiref | {{harvnb|Manley|2009|pp=4, 15, 32}} | {{harvnb|Sider|2009|pp=386–387}} }}</ref> This view is opposed by so-called ''serious metaphysicians'', who contend that metaphysical disputes are about substantial features of the underlying structure of reality.<ref>{{multiref | {{harvnb|Manley|2009|pp=28, 36}} | {{harvnb|Kriegel|2016|pp=272–273}} }}</ref> A closely related debate between ontological [[Philosophical realism|realists]] and anti-realists concerns the question of whether there are any objective facts that determine which metaphysical theories are true.<ref>{{multiref | {{harvnb|Chalmers|2009|pp=77–78}} | {{harvnb|Loux|Crisp|2017|pp=304–305}} | {{harvnb|Tahko|2015|pp=65–66, 68}} }}</ref> A different criticism, formulated by [[Pragmatism|pragmatists]], sees the fault of metaphysics not in its cognitive ambitions or the meaninglessness of its statements, but in its practical irrelevance and lack of usefulness.<ref>{{multiref | {{harvnb|Koons|Pickavance|2015|p=5}} | {{harvnb|Macarthur|2020|p=[https://books.google.com/books?id=ra7QDwAAQBAJ&pg=PA166 166]}} }}</ref>

[[Martin Heidegger]] criticized traditional metaphysics, saying that it fails to distinguish between individual entities and being as their ontological ground. His attempt to reveal the underlying assumptions and limitations in the history of metaphysics to "overcome metaphysics" influenced [[Jacques Derrida]]'s method of [[deconstruction]].<ref>{{multiref | {{harvnb|Wheeler|2020|loc=§ 1. Biographical Sketch, § 2.2.1 The Question, § 3.3 Technology}} | {{harvnb|Gilje|Skirbekk|2017|pp=[https://books.google.com/books?id=_I00e3SQAwMC&pg=PA463 463–464]}} | {{harvnb|Holland|loc=Lead Section}} | {{harvnb|Beaulieu|Kazarian|Sushytska|2014|pp=[https://books.google.com/books?id=d4PzBQAAQBAJ&pg=PA3 3–4]}} | {{harvnb|George|2015|p=[https://books.google.com/books?id=Ym7vCAAAQBAJ&pg=PA2 2]}} }}</ref> Derrida employed this approach to criticize metaphysical texts for relying on opposing terms, like presence and absence, which he thought were inherently unstable and contradictory.<ref>{{multiref | {{harvnb|Reynolds|loc=Lead Section, § 2. Deconstructive Strategy}} | {{harvnb|Gilje|Skirbekk|2017|pp=[https://books.google.com/books?id=_I00e3SQAwMC&pg=PA463 463–464]}} | {{harvnb|Holland|loc=Lead Section}} }}</ref>

There is no consensus about the validity of these criticisms and whether they affect metaphysics as a whole or only certain issues or approaches in it. For example, it could be the case that certain metaphysical disputes are merely verbal while others are substantive.<ref>{{harvnb|Rea|2021|pp=215–216, 223–224}}</ref>

== Relation to other disciplines ==
Metaphysics is related to many fields of inquiry by investigating their basic concepts and relation to the fundamental structure of reality. For example, the natural sciences rely on concepts such as [[Scientific law|law of nature]], causation, necessity, and spacetime to formulate their theories and predict or explain the outcomes of experiments.<ref>{{multiref | {{harvnb|Göhner|Schrenk|loc=Lead Section, § 1. What Is Metaphysics of Science?}} | {{harvnb|Mumford|Tugby|2013|pp=1–2}} | {{harvnb|Hawley|2018|pp=187–188}} }}</ref> While scientists primarily focus on applying these concepts to specific situations, metaphysics examines their general nature and how they depend on each other. For instance, physicists formulate laws of nature, like [[Newton's law of universal gravitation|laws of gravitation]] and [[Laws of thermodynamics|thermodynamics]], to describe how physical systems behave under various conditions. Metaphysicians, by contrast, examine what all laws of nature have in common, asking whether they merely describe contingent regularities or express necessary relations.<ref>{{multiref | {{harvnb|Göhner|Schrenk|loc=§ 3. Why Do We Need Metaphysics of Science?, § 4c. Laws of Nature}} | {{harvnb|Roberts|2016|pp=337–338}} }}</ref> New scientific discoveries have also influenced existing metaphysical theories and inspired new ones. Einstein's [[theory of relativity]], for instance, prompted various metaphysicians to conceive space and time as a unified dimension rather than as independent dimensions.<ref>{{harvnb|Healey|2016|pp=356–357}}</ref> Empirically focused metaphysicians often rely on scientific theories to ground their theories about the nature of reality in empirical observations.<ref>{{harvnb|Hawley|2018|pp=187–188}}</ref>

Similar issues arise in the [[social sciences]] where metaphysicians investigate their basic concepts and analyze their metaphysical implications. This includes questions like whether social facts emerge from non-social facts, whether social groups and institutions have mind-independent existence, and how they persist through time.<ref>{{harvnb|Hawley|2018|pp=188–189}}</ref> Metaphysical assumptions and topics in [[psychology]] and [[psychiatry]] include the questions about the relation between body and mind, whether the nature of the human mind is historically fixed, and what the metaphysical status of diseases is.<ref>{{multiref | {{harvnb|Dafermos|2021|pp=1–2, 6–7}} | {{harvnb|Hawley|2016|p=174}} }}</ref>

Metaphysics is similar to both [[physical cosmology]] and [[theology]] in its exploration of the first causes and the universe as a whole. Key differences are that metaphysics relies on rational inquiry while physical cosmology gives more weight to empirical observations and theology incorporates divine [[revelation]] and other faith-based doctrines.<ref>{{multiref | {{harvnb|Van Inwagen|2024|pp=6–8}} | {{harvnb|Loux|Crisp|2017|p=10}} }}</ref> Historically, cosmology and theology were considered subfields of metaphysics.<ref>{{multiref | {{harvnb|Dryer|2016|p=[https://books.google.com/books?id=S8weDAAAQBAJ&pg=PA490 490]}} | {{harvnb|Loux|Crisp|2017|p=10}} }}</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}}
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}}

[[Computer science|Computer scientists]] rely on metaphysics in the form of ontology to represent and classify objects. They develop conceptual frameworks, called ''ontologies'', for limited domains,<ref name="auto2">{{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> such as a database with categories like ''person'', ''company'', ''address'', and ''name'' to represent information about clients and employees.<ref>{{harvnb|Kozierkiewicz|Pietranik|2019|p=[https://books.google.com/books?id=2uWPDwAAQBAJ&pg=PA24 24]}}</ref> Ontologies provide standards for encoding and storing information in a structured way, allowing computational processes to use the information for various purposes.<ref name="auto2"/> [[Upper ontology|Upper ontologies]], such as [[Suggested Upper Merged Ontology]] and [[Basic Formal Ontology]], define concepts at a more abstract level, making it possible to integrate information belonging to different domains.<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>

[[Logic]] as the study of [[Logical reasoning|correct reasoning]]<ref>{{multiref |1={{harvnb|MacFarlane|2017}} |2={{harvnb|Corkum|2015|pp=753–767}} |3={{harvnb|Blair|Johnson|2000|pp=93–95}} |4={{harvnb|Magnus|2005|loc=1.6 Formal Languages|pp=12–14}} }}</ref> is often used by metaphysicians to engage in their inquiry and express insights through precise [[logical formula]]s.<ref>{{harvnb|Ney|2014|pp=1–2, 18–20}}</ref> Another relation between the two fields concerns the metaphysical assumptions associated with [[logical system]]s. Many logical systems like [[first-order logic]] rely on [[existential quantifier]]s to express existential statements. For instance, in the logical formula <math>\exists x \text{Horse}(x)</math> the existential quantifier <math>\exists</math> is applied to the [[Predicate (logic)|predicate]] <math>\text{Horse}</math> to express that there are horses. Following Quine, various metaphysicians assume that existential quantifiers carry [[ontological commitment]]s, meaning that existential statements imply that the entities over which one quantifies are part of reality.<ref>{{multiref |1={{harvnb|Shapiro|Kouri Kissel|2022|loc=§2.1 Building Blocks}} |2={{harvnb|Cook|2009|p=[https://books.google.com/books?id=JfaqBgAAQBAJ&pg=PA111 111]}} |3={{harvnb|Kind|2018|p=[https://books.google.com/books?id=oDhjDwAAQBAJ&pg=PT236 236]}} |4={{harvnb|Casati|Fujikawa|loc=Lead Section, §1. Existence as a Second-Order Property and Its Relation to Quantification}} }}</ref>

== History ==
{{main|History of metaphysics}}

[[File:Yin yang.svg|thumb|right|upright=0.8|alt=Symbol of yin and yang. It has a circular shape split into two swirling halves. One half is black with a white dot inside. The other half is white with a black dot inside.|The [[taijitu]] symbol shows [[yin and yang]], which are two correlated forces discussed in Chinese metaphysics to explore the nature and patterns of existence.<ref>{{multiref | {{harvnb|Perkins|2023|loc=Lead Section}} | {{harvnb|Littlejohn|loc=§ 5. Fundamental Concepts in the Daodejing}} }}</ref>]]

Metaphysics originated in the ancient period from speculations about the nature and origin of the cosmos.<ref>{{multiref | {{harvnb|Hancock|2006|p=183}} | {{harvnb|Hamlyn|2005|p=590}} }}</ref> In [[ancient India]], starting in the 7th century BCE, the [[Upanishads]] were written as religious and philosophical texts that examine how [[Brahman|ultimate reality]] constitutes the ground of all being. They further explore the nature of the [[Ātman (Hinduism)|self]] and how it can reach [[moksha|liberation]] by understanding ultimate reality.<ref>{{multiref | {{harvnb|Perrett|2016|pp=[https://books.google.com/books?id=q7wwCwAAQBAJ&pg=PA7 7–10]}} | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} | {{harvnb|Andrea|Overfield|2015|pp=[https://books.google.com/books?id=x5-aBAAAQBAJ&pg=PA70 70–71]}} }}</ref> This period also saw the emergence of [[Buddhism]] in the 6th century BCE,{{efn|The precise date is disputed.<ref>{{harvnb|Velez|loc=§ 1a. Dates}}</ref>}} which denies the existence of an independent self and understands the world as a [[Saṃsāra|cyclic process]].<ref>{{multiref | {{harvnb|Perrett|2016|pp=[https://books.google.com/books?id=q7wwCwAAQBAJ&pg=PA7 7–10]}} | {{harvnb|Velez|loc=Lead Section, § 3. The Buddha's Cosmology and Metaphysics}} | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} }}</ref> At about the same time{{efn|According to traditional accounts, [[Laozi]] as the founder of Daoism lived in the 6th century BCE but other accounts state that he may have lived in the 4th or 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>}} in [[ancient China]], the school of [[Daoism]] was formed and explored the natural order of the universe, known as [[Dao]], and how it is characterized by the interplay of [[yin and yang]] as two correlated forces.<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]}} | {{harvnb|Wang|Bao|Guan|2020|p=[https://books.google.com/books?id=gSfXDwAAQBAJ&pg=PA3 3]}} }}</ref>

In [[ancient Greece]], metaphysics emerged in the 6th century BCE with the [[pre-Socratic]] philosophers, who gave rational explanations of the cosmos as a whole by examining the [[first principle]]s from which everything arises.<ref>{{multiref | {{harvnb|Hancock|2006|p=183}} | {{harvnb|Hamlyn|2005|p=590}} | {{harvnb|Kirk|2004|pp=[https://books.google.com/books?id=uewoLyIw_DQC&pg=PA308 308–310]}} }}</ref> Building on their work, [[Plato]] (427–347 BCE) formulated his [[theory of forms]], which states that eternal forms or ideas possess the highest kind of reality while the material world is only an imperfect reflection of them.<ref>{{multiref | {{harvnb|Hancock|2006|pp=184–185}} | {{harvnb|Hamlyn|2005|p=590}} | {{harvnb|Graham|loc=§ 3b. Metaphysics}} }}</ref> [[Aristotle]] (384–322 BCE) accepted Plato's idea that there are universal forms but held that they cannot exist on their own but depend on matter. He also proposed a system of categories and developed a comprehensive framework of the natural world through his theory of the [[four causes]].<ref>{{multiref | {{harvnb|Hancock|2006|pp=185–187}} | {{harvnb|Hamlyn|2005|p=590}} | {{harvnb|Graham|loc=§ 4a. Terminology, § 4f. Metaphysics}} }}</ref> Starting in the 4th century BCE, [[Hellenistic philosophy]] explored the [[Logos|rational order]] underlying the cosmos and the laws governing it.<ref>{{multiref | {{harvnb|Hamlyn|2005|p=590}} | {{harvnb|Graham|loc=§ 5a. Epicureanism, § 5c. The Stoics}} }}</ref> [[Neoplatonism]] emerged towards the end of the ancient period in the 3rd century CE and introduced the idea of "the One" as the transcendent and ineffable source of all creation.<ref>{{multiref | {{harvnb|Hancock|2006|pp=187–188}} | {{harvnb|Hamlyn|2005|pp=590–591}} | {{harvnb|Graham|loc=§ 5. Post-Hellenistic Thought}} }}</ref>{{efn|Influential Neoplatonists include [[Plotinus]], [[Porphyry (philosopher)|Porphyry]], [[Iamblichus]], [[Hypatia]], and [[Proclus]].<ref>{{multiref | {{harvnb|Wildberg|2021|loc=§ 1. Historical Orientation: Antiquity}} | {{harvnb|Remes|2014|pp=[https://books.google.com/books?id=MKrCBQAAQBAJ&pg=PA2 2, 25]}} }}</ref>}}

Meanwhile, in [[Indian Buddhism]], the [[Madhyamaka|Madhyamaka school]] developed the idea that all phenomena are [[Sunyata|inherently empty]] without a permanent essence. The consciousness-only doctrine of the [[Yogācāra|Yogācāra school]] stated that experienced objects are mere transformations of consciousness and do not reflect external reality.<ref>{{multiref | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} | {{harvnb|Depraz|Varela|Vermersch|2003|p=[https://books.google.com/books?id=iYJy_2909NAC&pg=PA212 212]}} | {{harvnb|Shun'ei|2014|pp=[https://books.google.com/books?id=1C4qAwAAQBAJ&pg=PA5 5–6]}} }}</ref> The [[Āstika and nāstika|Hindu school]] of [[Samkhya]] philosophy{{efn|The ideas underlying Samkhya philosophy arose as early as the 7th and 6th centuries BCE but its classical and systematic formulation is dated 350 CE.<ref name="auto1">{{multiref | {{harvnb|Ruzsa|loc=Lead Section}} | {{harvnb|Grayling|2019|loc=§ Indian Philosophy}} }}</ref>}} introduced a metaphysical dualism with [[Purusha|pure consciousness]] and [[Prakṛti|matter]] as its fundamental categories.<ref name="auto1"/> In China, the school of [[Xuanxue]] explored metaphysical problems such as the contrast 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>

[[File:Boethius.jpeg|thumb|alt=Medieval illustration showing Boethius from the front against a light background in a sitting position, dressed in green clothes with a red cloak|[[Boethius]]'s theory of universals influenced many subsequent metaphysicians.]]

Medieval Western philosophy was profoundly shaped by ancient Greek thought as philosophers integrated these ideas with [[Christian philosophy|Christian teachings]]. [[Boethius]] (477–524 CE) sought to reconcile Plato's and Aristotle's theories of universals, proposing that universals can exist both in matter and mind. His theory inspired the development of nominalism and conceptualism, as in the thought of [[Peter Abelard]] (1079–1142 CE).<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) understood metaphysics as the discipline investigating different meanings of ''being'', such as the contrast between substance and [[Accident (philosophy)|accident]], and principles applying to all beings, such as the [[principle of identity]].<ref>{{multiref | {{harvnb|Brown|loc=§ 5. Metaphysics}} | {{harvnb|Hancock|2006|p=189}} }}</ref> [[William of Ockham]] (1285–1347 CE) developed a methodological principle, known as [[Ockham's razor]], to choose between competing metaphysical theories.<ref>{{multiref | {{harvnb|Hancock|2006|p=190}} | {{harvnb|Grayling|2019|loc=§ Ockham}} }}</ref> Arabic–Persian philosophy flourished from [[Islamic Golden Age|the early 9th century CE to the late 12th century CE]], integrating ancient Greek philosophies to interpret and clarify the teachings of the [[Quran]].<ref>{{multiref | {{harvnb|Grayling|2019|loc=Arabic–Persian Philosophy}} | {{harvnb|Adamson|Taylor|2004|pp=1–3}} }}</ref> [[Avicenna]] (980–1037 CE) developed a comprehensive philosophical system that examined the contrast between existence and essence and distinguished between contingent and necessary existence.<ref>{{multiref | {{harvnb|Grayling|2019|loc=§ Ibn Sina (Avicenna)}} | {{harvnb|Lizzini|2021|loc=Lead Section, § 3. Essence and Existence, § 4. Modality and Existence}} }}</ref> [[Medieval India]] saw the emergence of the [[Monism|monist]] school of [[Advaita Vedanta]] in the 8th century CE, which holds that everything is one and that the idea of many entities existing independently 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}} | {{harvnb|Rangaswami|2012|p=[https://books.google.com/books?id=2snhxaaWDAYC&pg=PA114 114]}} }}</ref> In China, [[Neo-Confucianism]] arose in the 9th century CE and explored the [[Li (neo-Confucianism)|concept of li]] as the rational principle that is the ground of being and reflects the order of the universe.<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>

In the early modern period and following renewed interest in Platonism during the [[Renaissance]], [[René Descartes]] (1596–1650) developed a substance dualism according to which body and mind exist as independent entities 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> This idea was rejected by [[Baruch Spinoza]] (1632–1677), who formulated a monist philosophy suggesting that there is only one substance with both physical and mental attributes that develop side-by-side without interacting.<ref>{{multiref | {{harvnb|Hancock|2006|p=190}} | {{harvnb|Hamlyn|2005|p=591}} }}</ref> [[Gottfried Wilhelm Leibniz]] (1646–1716) introduced the concept of possible worlds and articulated a metaphysical system known as [[monadology]], which views the universe as a collection of [[Monad (philosophy)|simple substances]] synchronized without causal interaction.<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> [[Christian Wolff (philosopher)|Christian Wolff]] (1679–1754), conceptualized the scope of metaphysics by distinguishing between general and special metaphysics.<ref>{{multiref | {{harvnb|Svare|2006|p=[https://books.google.com/books?id=60MsUE3K2ekC&pg=PA15 15]}} | {{harvnb|Hettche|Dyck|2019|loc=§ 5. Metaphysics}} }}</ref> According to the [[idealism]] of [[George Berkeley]] (1685–1753), everything is mental, including material objects, which are [[Esse est percipi|ideas perceived by the mind]].<ref>{{multiref | {{harvnb|Hancock|2006|p=192}} | {{harvnb|Hamlyn|2005|p=591}} }}</ref> [[David Hume]] (1711–1776) made various contributions to metaphysics, including the [[Humeanism#Causality and necessity|regularity theory of causation]] and the idea that there are no necessary connections between distinct entities. Inspired by the [[empiricism]] of [[Francis Bacon]] (1561–1626) and [[John Locke]] (1632–1704), Hume criticized metaphysical theories that seek ultimate principles inaccessible to sensory experience.<ref>{{multiref | {{harvnb|Morris|Brown|2023|loc=§ 3. Philosophical Project, § 5. Causation, § 6. The Idea of Necessary Connection}} | {{harvnb|Hamlyn|2005|pp=591–592}} | {{harvnb|Waxman|2006|p=488}} }}</ref> This critical outlook was embraced by [[Immanuel Kant]] (1724–1804), who tried to reconceptualize metaphysics as an inquiry into the basic principles and categories of thought and understanding rather than seeing it as an attempt to comprehend mind-independent reality.<ref>{{multiref | {{harvnb|Hancock|2006|pp=192–193}} | {{harvnb|Hamlyn|2005|p=592}} | {{harvnb|Wood|2009|p=[https://books.google.com/books?id=i7PG-Vk824UC&pg=PA354 354]}} | {{harvnb|Loux|Crisp|2017|pp=1–2, 6}} }}</ref>

Many developments in the later modern period were shaped by Kant's philosophy. [[German idealism|German idealists]] adopted his idealistic outlook in their attempt to find a unifying principle as the foundation of all reality.<ref>{{multiref | {{harvnb|Hancock|2006|p=193}} | {{harvnb|Hamlyn|2005|p=592}} | {{harvnb|Critchley|2001|p=[https://books.google.com/books?id=syhsLJ1eMOEC&pg=PA31 31]}} }}</ref> [[Georg Wilhelm Friedrich Hegel]]'s (1770–1831) idealistic contention is that reality is conceptual all the way down, and being itself is rational.<ref>{{multiref | {{harvnb|Houlgate|2005|p=106}} | {{harvnb|Stern|2008|p=172}} }}</ref> He inspired the [[British idealism]] of [[Francis Herbert Bradley]] (1846–1924), who interpreted Hegel's concept of [[Absolute idealism|absolute spirit]] as the all-inclusive totality of being.<ref>{{multiref | {{harvnb|Hancock|2006|p=193}} | {{harvnb|Hamlyn|2005|p=592}} | {{harvnb|Grayling|2019|loc=§ Idealism}} }}</ref> [[Arthur Schopenhauer]] (1788–1860) was a strong critic of German idealism and articulated a different [[The World as Will and Representation|metaphysical vision]], positing a [[Voluntarism (philosophy)#Metaphysical voluntarism|blind and irrational will as the underlying principle of reality]].<ref>{{multiref | {{harvnb|Grayling|2019|loc=§ Schopenhauer}} | {{harvnb|Janaway|1999|pp=[https://academic.oup.com/book/2954/chapter-abstract/143638920?redirectedFrom=fulltext 248–249]}} | {{harvnb|Barua|2018|pp=[https://books.google.com/books?id=mqVFDwAAQBAJ&pg=PA2 2–3]}} }}</ref> Pragmatists like [[C. S. Peirce]] (1839–1914) and  [[John Dewey]] (1859–1952) conceived metaphysics as an observational science of the most general features of reality and experience.<ref>{{multiref | {{harvnb|Hancock|2006|p=194}} | {{harvnb|Misak|2008|loc=[https://books.google.com/books?id=p30osmyc2xoC&pg=PA406 Scientific Realism, Anti-Realism, and Empiricism]}} }}</ref>

[[File:ANWhitehead.jpg|thumb|alt=Photo showing Alfred North Whitehead from the front against a dark background looking at the camera, dressed in formal dark-colored attire with a high-collared white shirt below|[[Alfred North Whitehead]] articulated the foundations of [[process philosophy]] in his work ''[[Process and Reality]]''.]]

At the turn of the 20th century in [[analytic philosophy]], philosophers such as [[Bertrand Russell]] (1872–1970) and [[G. E. Moore]] (1873–1958) led a "revolt against idealism", arguing for the existence of a mind-independent world aligned with common sense and empirical science.<ref>{{multiref | {{harvnb|Griffin|2013|pp=383, 396, 399–402}} | {{harvnb|Peters|2021|pp=[https://books.google.com/books?id=UakWEAAAQBAJ&pg=PA31 31–32]}} }}</ref> [[Logical atomism|Logical atomists]], like Russell and the early [[Ludwig Wittgenstein]] (1889–1951), conceived the world as a multitude of atomic facts, which later inspired metaphysicians such as [[D. M. Armstrong]] (1926–2014).<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]}}}}</ref> [[Alfred North Whitehead]] (1861–1947) developed [[process philosophy|process metaphysics]] as an attempt to provide a holistic description of both the objective and the subjective realms.<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) and other [[Logical positivism|logical positivists]] formulated a wide-ranging criticism of metaphysical statements, arguing that they are meaningless because there is no way to [[Verificationism|verify them]].<ref>{{multiref | {{harvnb|Hamlyn|2005|p=592}} | {{harvnb|Hart|1998|loc=Lead Section}} | {{harvnb|Dharamsi|2017|p=[https://books.google.com/books?id=DFbJDgAAQBAJ&pg=PA368 368]}} }}</ref> Other criticisms of traditional metaphysics identified misunderstandings of [[Ordinary language philosophy|ordinary language]] as the source of many traditional metaphysical problems or challenged complex metaphysical deductions by appealing to common sense.<ref>{{multiref | {{harvnb|Hancock|2006|pp=194–195}} | {{harvnb|Morris|2017|p=[https://books.google.com/books?id=sfElDgAAQBAJ&pg=PA15 15]}} | {{harvnb|Baldwin|2010|loc=§ 2. The Refutation of Idealism, § 6. Common Sense and Certainty}} }}</ref>  

The decline of logical positivism led to a revival of metaphysical theorizing.<ref>{{harvnb|Broadbent|2016|p=[https://books.google.com/books?id=_GSFCwAAQBAJ&pg=PA145 145]}}</ref> [[Willard Van Orman Quine]] (1908–2000) tried to naturalize metaphysics by connecting it to the empirical sciences. His student [[David Lewis (philosopher)|David Lewis]] (1941–2001) employed the concept of possible worlds to formulate his [[modal realism]].<ref>{{multiref | {{harvnb|Hylton|2007|p=[https://books.google.com/books?id=n5XX3CwWh2MC&pg=PT348 348]}} | {{harvnb|Oddie|2006|p=170}} | {{harvnb|Parent|loc=§ 2. Lewis' Realism}} }}</ref> [[Saul Kripke]] (1940–2022) helped revive discussions of identity and [[Scientific essentialism|essentialism]], distinguishing [[Metaphysical necessity|necessity]] as a metaphysical notion from the [[Epistemology|epistemic]] notion of ''[[A priori and a posteriori|a priori]]''.<ref>{{multiref | {{harvnb|Ahmed|2010|p=[https://books.google.com/books?id=dkkdCgAAQBAJ&pg=PA3 3]}} | {{harvnb|Gutting|2009|pp=[https://books.google.com/books?id=4WuaB_0nu8wC&pg=PA31 31–32]}} }}</ref>

In [[continental philosophy]], [[Edmund Husserl]] (1859–1938) engaged in ontology through a phenomenological description of experience, while his student [[Martin Heidegger]] (1889–1976) developed [[fundamental ontology]] to clarify the meaning of being.<ref>{{multiref | {{harvnb|Smith|2018|loc=Lead Section, § 5. Phenomenology and Ontology, Epistemology, Logic, Ethics}} | {{harvnb|McLean|2003|p=[https://www.encyclopedia.com/philosophy-and-religion/philosophy/philosophy-terms-and-concepts/metaphysics 550]}} | {{harvnb|Taminiaux|1991|p=[https://books.google.com/books?id=kcJzeXpHctYC&pg=PA154 154]}} }}</ref> Heidegger's philosophy inspired [[Jacques Derrida]]'s (1930–2004) criticism of metaphysics.<ref>{{multiref | {{harvnb|Gilje|Skirbekk|2017|loc=Derrida, Foucault, and Rorty – Deconstruction and Critique}} | {{harvnb|Reynolds|loc=Lead Section}} }}</ref> [[Gilles Deleuze]]'s (1925–1995) approach to metaphysics challenged traditionally influential concepts like substance, essence, and identity by reconceptualizing the field through alternative notions such as multiplicity, event, and difference.<ref>{{multiref | {{harvnb|Smith|Protevi|Voss|2023|loc=Lead Section}} | {{harvnb|Roberts|2016a|p=[https://books.google.com/books?id=UKW5DAAAQBAJ&pg=PA149 149]}} }}</ref>

==See also==
* [[Computational metaphysics]]
* [[Doctor of Metaphysics]]
* [[Enrico Berti#Thought|Enrico Berti's classification of metaphysics]]
* [[Feminist metaphysics]]
* [[Fundamental question of metaphysics]]
* [[List of metaphysicians]]
* [[Grounding (metaphysics)|Metaphysical grounding]]

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

===Citations===
{{reflist}}

===Sources===
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* {{cite journal |last1=Van Miltenburg |first1=Niels |title=Causality, Determination and Free Will: Towards an Anscombean Account of Free Action |journal=Synthese |volume=200 |issue=4 |doi=10.1007/s11229-022-03700-3 |date=2022 |doi-access=free }}
* {{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 web |last1=Velez |first1=Abraham |title=Buddha |url=https://iep.utm.edu/buddha/ |website=Internet Encyclopedia of Philosophy |access-date=30 March 2024 |archive-date=4 February 2024 |archive-url=https://web.archive.org/web/20240204123126/https://iep.utm.edu/buddha/ |url-status=live }}
* {{cite web |last1=Vihvelin |first1=Kadri |title=Arguments for Incompatibilism |url=https://plato.stanford.edu/entries/incompatibilism-arguments/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=1 May 2024 |date=2022 }}
* {{cite book |last1=Wang |first1=Yueqing |last2=Bao |first2=Qinggang |last3=Guan |first3=Guoxing |title=History of Chinese Philosophy Through Its Key Terms |publisher=Nanjing University Press |isbn=978-981-15-2572-8 |chapter-url=https://books.google.com/books?id=gSfXDwAAQBAJ&pg=PA3 |language=en |chapter=1. Way (Dao, 道) |date=2020 |pages=1–18 }}
* {{cite book |last1=Wardy |first1=Robert |chapter=Categories |chapter-url=https://www.rep.routledge.com/articles/thematic/categories/v-1 |title=Routledge Encyclopedia of Philosophy |publisher=Routledge |access-date=22 March 2024 |language=en |date=1998 |doi=10.4324/9780415249126-N005-1 |isbn=978-0-415-25069-6 |archive-date=22 March 2024 |archive-url=https://web.archive.org/web/20240322183105/https://www.rep.routledge.com/articles/thematic/categories/v-1 |url-status=live }}
* {{cite book |last1=Waxman |first1=Wayne |editor1-last=Borchert |editor1-first=Donald M. |title=The Encyclopedia of Philosophy. 4: Gadamer – Just War Theory |publisher=Macmillan |isbn=0-02-865784-5 |edition=2 |chapter=David Hume (1711–1776) |date=2006 |chapter-url=https://www.encyclopedia.com/people/philosophy-and-religion/philosophy-biographies/david-hume |pages=486–514 }}
* {{cite web |last1=Weatherson |first1=Brian |title=The Problem of the Many |url=https://plato.stanford.edu/entries/problem-of-many/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=19 November 2024 |date=2023 }}
* {{cite web |last1=Weisberg |first1=Josh |title=Hard Problem of Consciousness |url=https://iep.utm.edu/hard-problem-of-conciousness/ |website=Internet Encyclopedia of Philosophy |access-date=27 March 2024 |archive-date=19 July 2023 |archive-url=https://web.archive.org/web/20230719172212/https://iep.utm.edu/hard-problem-of-conciousness/ |url-status=live }}
* {{cite web |last1=Wheeler |first1=Michael |title=Martin Heidegger |url=https://plato.stanford.edu/entries/heidegger/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=11 August 2024 |date=2020 }}
* {{cite book |last1=White |first1=Alan |title=Methods of Metaphysics |date=2019 |publisher=Routledge |isbn=978-0-429-51427-2 |language=en }}
* {{cite web |last1=Wiland |first1=Eric |last2=Driver |first2=Julia |title=Gertrude Elizabeth Margaret Anscombe |url=https://plato.stanford.edu/entries/anscombe/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=23 November 2024  |date=2022 }}
* {{cite web |last1=Wildberg |first1=Christian |title=Neoplatonism |url=https://plato.stanford.edu/entries/neoplatonism/ |website=The Stanford Encyclopedia of Philosophy |publisher=Metaphysics Research Lab, Stanford University |access-date=22 November 2024  |date=2021 }}
* {{cite book |last1=Willaschek |first1=Marcus |author-link1=Marcus Willaschek |title=Kant on the Sources of Metaphysics: The Dialectic of Pure Reason |publisher=Cambridge University Press |isbn=978-1-108-59607-7 |url=https://books.google.com/books?id=wmjtDwAAQBAJ&pg=PA43 |language=en |date=2018 }}
* {{cite book |last1=Williamson |first1=John |editor1-last=Beebee |editor1-first=Helen |editor2-last=Hitchcock |editor2-first=Christopher |editor3-last=Menzies |editor3-first=Peter |title=The Oxford Handbook of Causation |publisher=Oxford University Press |isbn=978-0-19-162946-4 |chapter-url=https://books.google.com/books?id=yWWEIvNgUQ4C&pg=PA186 |language=en |chapter=Probabilistic Theories |date=2012 |pages=185–212}}
* {{cite journal |last1=Wilsch |first1=Tobias |title=Sophisticated Modal Primitivism |journal=Philosophical Issues |date=2017 |volume=27 |issue=1 |pages=428–448 |doi=10.1111/phis.12100 }}
* {{cite book |last1=Wood |first1=Allen W. |editor1-last=Kim |editor1-first=Jaekwon |editor2-last=Sosa |editor2-first=Ernest |editor3-last=Rosenkrantz |editor3-first=Gary S. |title=A Companion to Metaphysics |date=2009 |publisher=John Wiley & Sons |isbn=978-1-4443-0853-2 |chapter-url=https://books.google.com/books?id=i7PG-Vk824UC&pg=PA354 |language=en |chapter=Kantianism |pages=353–358 }}
* {{cite book |last1=Wu |first1=Guo |title=An Anthropological Inquiry Into Confucianism: Ritual, Emotion, and Rational Principle |publisher=Rowman & Littlefield |isbn=978-1-7936-5432-8 |url=https://books.google.com/books?id=zRVmEAAAQBAJ |language=en |date=2022 }}
{{Refend}}

==External links==
{{Library resources box}}
* {{PhilPapers|category|metaphysics}}
* {{InPho|taxonomy|2350}}
* {{cite IEP |url-id=category/m-and-e/metaphysics/ |title=Metaphysics}}
* [https://www.britannica.com/EBchecked/topic/377923/metaphysics Metaphysics] at [[Encyclopædia Britannica]]
* {{librivox book |title=Metaphysics}}

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