View source for Epistemic closure

{{short description|Principle in epistemology}}
{{Other uses|Closure (disambiguation){{!}}Closure}}

'''Epistemic closure'''<ref name="stanford">{{cite encyclopedia |author=Luper, Steven |title=The Epistemic Closure Principle |date=31 December 2001 |encyclopedia=[[Stanford Encyclopedia of Philosophy]] |publisher= Metaphysics Research Lab, Stanford University|chapter-url=http://plato.stanford.edu/entries/closure-epistemic/#CloPri|chapter=Epistemic Closure }}</ref> is a [[property (philosophy)|property]] of some [[belief system]]s. It is the [[concept|principle]] that if a subject <math>S</math> knows <math>p</math>, and <math>S</math> knows that <math>p</math> [[Logical consequence|entails]] <math>q</math>, then <math>S</math> can thereby come to know <math>q</math>. Most [[epistemology|epistemological]] theories involve a closure principle and many [[Skepticism|skeptical]] arguments assume a closure principle.

On the other hand, some epistemologists, including [[Robert Nozick]], have denied closure principles on the basis of [[reliabilism|reliabilist]] accounts of knowledge. Nozick, in ''[[Philosophical Explanations]]'', advocated that, when considering the [[Gettier problem]], the least counter-intuitive assumption we give up should be epistemic closure. Nozick suggested a "truth tracking" theory of knowledge, in which the x was said to know P if x's belief in P tracked the truth of P through the relevant [[modal logic|modal scenarios]].<ref>''Philosophical explanations'',  By Robert Nozick (Harvard 1981), page 204</ref>

A subject may not actually believe <var>q</var>, for example, regardless of whether he or she is justified or warranted. Thus, one might instead say that knowledge is closed under ''known'' deduction: if, while knowing <var>p</var>, <var>S</var> believes <var>q</var> because <var>S</var> knows that <var>p</var> entails <var>q</var>, then <var>S</var> knows <var>q</var>.<ref name="stanford" /> An even stronger formulation would be as such: If, while knowing various propositions, <var>S</var> believes <var>p</var> because <var>S</var> knows that these propositions entail <var>p</var>, then <var>S</var> knows <var>p</var>.<ref name="stanford" /> While the principle of epistemic closure is generally regarded as intuitive,<ref>{{cite journal |author1=Brady, Michael |author2=Pritchard, Duncan |title=Epistemological Contextualism: Problems and Prospects |journal=[[The Philosophical Quarterly]] |volume=55 |issue=219 |pages=161–171 |year=2005 |doi=10.1111/j.0031-8094.2005.00393.x }}</ref> philosophers such as Robert Nozick and [[Fred Dretske]] have argued against it.<ref>[https://plato.stanford.edu/entries/closure-epistemic/ "Epistemic Closure"]. ''[[Stanford Encyclopedia of Philosophy]].''</ref>

== Epistemic closure and skeptical arguments ==
The epistemic closure principle typically takes the form of a [[modus ponens]] argument:

# S knows p.
# S knows that p entails q.
# Therefore, S knows q.

This epistemic closure principle is central to many versions of skeptical arguments.  A [[Skepticism|skeptical]] argument of this type will involve knowledge of some piece of widely accepted information to be knowledge, which will then be pointed out to entail knowledge of some skeptical scenario, such as the [[brain in a vat]] scenario or the [[Evil demon|Cartesian evil demon]] scenario.  A skeptic might say, for example, that if you know that you have hands, then you know that you are not a handless brain in a vat (because knowledge that you have hands implies that you know you are not handless, and if you know that you are not handless, then you know that you are not a handless brain in a vat).<ref>{{Cite journal|last=Sosa|first=Ernest|date=1999-10-01|title=How to Defeat Opposition to Moore|journal=Noûs|language=en|volume=33|pages=141–153|doi=10.1111/0029-4624.33.s13.7|issn=1468-0068}}</ref>  The skeptic will then utilize this conditional to form a [[modus tollens]] argument.  For example, the skeptic might make an argument like the following:
# You do not know that you are not a handless brain in a vat (~K(~h))
# If you know that you have hands, then you know that you are not a handless brain in a vat (K(o) → K(~h))
# '''Conclusion:''' Therefore, you do not know that you have hands (~K(o))
Much of the epistemological discussion surrounding this type of skeptical argument involves whether to accept or deny the conclusion, and how to do each.  [[Ernest Sosa]] says that there are three possibilities in responding to the skeptic:
# Agree with the skeptic by granting him both premises and the conclusion (1, 2, c)
# Disagree with the skeptic by denying premise 2 and the conclusion, but maintaining premise 1 (1, ~2, ~c) as [[Robert Nozick|Nozick]] and [[Fred Dretske|Dretske]] do.  This amounts to ''denying'' the epistemic closure principle.
# Disagree with the skeptic by denying premise 1 and the conclusion, but maintaining premise 2 (~1, 2, ~c) as [[G. E. Moore|Moore]] does.  This amounts to ''maintaining'' the epistemic closure principle, and holding that knowledge is closed under known [[Logical consequence|implication]].

== Justificatory closure == 
In the seminal 1963 paper, “[[Gettier problem|Is Justified True Belief Knowledge?]]”, Edmund Gettier gave an assumption (later called the “principle of deducibility for justification” by [[Irving Thalberg, Jr.]])<ref>{{cite journal |author=Thalberg Jr., Irving |title=In Defense of Justified True Belief |journal=[[Journal of Philosophy]] |volume=66 |issue=22 |pages=794–803 |date=November 1969 |jstor=2024370 |ref={{harvid|Thalberg|1969}}|doi=10.2307/2024370 }}</ref> that would serve as a basis for the rest of his piece: “for any proposition P, if S is justified in believing P and P entails Q, and S deduces Q from P and accepts Q as a result of this deduction, then S is justified in believing Q.”<ref>{{cite journal |author=Gettier, Edmund |title=Is Justified True Belief Knowledge? |journal=[[Analysis (journal)|Analysis]] |volume=23 |issue=6 |pages=121–3 |date=June 1963 |jstor=3326922 |doi=10.1093/analys/23.6.121|url=https://halshs.archives-ouvertes.fr/halshs-01439314/file/2013%20Gettier%20Conocimiento.pdf }}</ref> This was seized upon by Thalberg, who rejected the principle in order to demonstrate that one of Gettier's examples fails to support Gettier's main thesis that justified true belief is not knowledge (in the following quotation, (1) refers to “Jones will get the job”, (2) refers to “Jones has ten coins”, and (3) is the [[logical conjunction]] of (1) and (2)):

<blockquote>Why doesn't Gettier's principle (PDJ) hold in the evidential situation he has described? You multiply your risks of being wrong when you believe a conjunction. […&nbsp;T]he most elementary theory of probability indicates that Smith's prospects of being right on both (1) and (2), namely, of being right on (3), are bound to be less favorable than his prospects of being right on either (1) or (2). In fact, Smith's chances of being right on (3) might not come up to the minimum standard of justification which (1) and (2) barely satisfy, and Smith would be unjustified in accepting (3). {{harv|Thalberg|1969|p=798}}</blockquote>

== In other uses==
=== Epistemic closure in U.S. political discussion ===
The term "epistemic closure" has been used in an unrelated sense in American political debate to refer to the claim that political belief systems can be closed systems of deduction, unaffected by [[empirical evidence]].<ref name=nyt>{{cite news |title='Epistemic Closure'? Those are Fighting Words |author=Patricia Cohen |url=https://www.nytimes.com/2010/04/28/books/28conserv.html?_r=0 |newspaper=[[The New York Times]] |date=27 April 2010 |access-date=28 November 2012}}</ref> This use of the term was popularized by libertarian blogger and commentator [[Julian Sanchez (writer)|Julian Sanchez]] in 2010 as an extreme form of [[confirmation bias]].<ref name="nyt" /><ref>{{cite web |author=Sanchez, Julian |title=Frum, Cocktail Parties, and the Threat of Doubt |date=26 March 2010 |url=http://www.juliansanchez.com/2010/03/26/frum-cocktail-parties-and-the-threat-of-doubt}}</ref>

==See also==
* [[Epistemic logic]]
* [[Doxastic logic]]
* {{annotated link|Here is one hand#Objections and replies}}
== References ==
{{reflist}}

==External links==
* {{cite SEP |url-id=closure-epistemic |title=The Epistemic Closure Principle}}
* {{InPho|idea|1133}}
* {{cite IEP |url-id=epis-clo/}}
* {{PhilPapers|search|Epistemic_closure}}

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[[Category:Concepts in epistemology]]
[[Category:Belief]]
[[Category:Epistemic logic]]
[[Category:Philosophy of Robert Nozick]]
[[Category:Concepts in logic]]