Unfair to Nozick

Page 1 of 5 Unfair to Nozick

PRINTED FROM OXFORD SCHOLARSHIP ONLINE (www.oxfordscholarship.com). (c) Copyright Oxford University Press, 2012.All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of amonograph in OSO for personal use (for details see http://www.oxfordscholarship.com/page/privacy-policy). Subscriber: Universityof Oxford; date: 29 January 2013

Essays on SkepticismAnthony Brueckner

Print publication date: 2010Print ISBN-13: 9780199585861Published to Oxford Scholarship Online: Jan-11DOI: 10.1093/acprof:oso/9780199585861.001.0001

Unfair to Nozick

Anthony Brueckner

DOI: 10.1093/acprof:oso/9780199585861.003.0028

Abstract and Keywords

This chapter defends Nozick from the charge that his position on scepticismbegs the question of whether one is in a normal world.

Keywords: Nozick, closure, tracking, Craig, normal world

Edward Craig argues that Nozick's ‘tracking’ analysis of knowledge is eitherimpotent or redundant as an anti‐sceptical weapon.1 Craig charges that theanalysis can be successfully deployed against the sceptic only if we are in aposition to assert that the actual world is not a sceptical world (is not a worldin which we are subject to systematic and comprehensive illusion). But if weare in such a position, then we must have already refuted the sceptic. I amafraid that I must add a few more words to the file on Nozick's anti‐scepticalstrategy in order to explain why Craig's charge is unfair.

Nozick (along with many others) sees the sceptic as arguing in the followingway. Let ‘SK’ stand for the proposition that I am a brain in a vat in a scepticalworld; let ‘P’ stand for a proposition I claim to know, e.g., that I am nowsitting; let ‘

’ stand for the strict conditional; let ‘→’ stand for the subjunctive conditional;let ‘K(s, ϕ)’ stand for the proposition that s knows that ϕ; and let ‘a’ stand forme. Then the sceptic can argue that I do not know that I am sitting in thismanner:

http://www.oxfordscholarship.com/page/privacy-policy



(1) [K(a,P) & K(a,P

∼SK)] → K(a, ∼SK)(2) K(a,P

∼SK)(3) ∼K(a, ∼SK)(4) ∼K(a,P)

As Craig in effect notes, Nozick's strategy is not to construct an argument,based on his analysis of knowledge, whose conclusion contradicts (4).This foolhardy strategy would require a showing that I satisfy Nozick's firstsubjunctive condition for knowing that P, i.e., a showing that in the worldsclose to the actual world in which I am not sitting. I do not mistakenly believethat I am sitting. If the actual world is in fact a sceptical world, then the close∼P‐worlds will also be sceptical worlds in which I do mistakenly believe thatP. So to show what needs showing on the fool‐hardy strategy, I would needto show that the actual world is not a sceptical world.

Craig is aware that Nozick's anti‐sceptical strategy instead concerns thesceptic's claim that if I know that P, then I know that ∼SK. More precisely,Nozick's strategy concerns premiss (1) in the target sceptical argument.What (p. 307 ) is the sceptic's justification for this premiss? It is held to bean instance of the general principle that knowledge is closed under knownentailment:

• ∀t∀ϕ∀ψ{[K(t,ϕ) &K(t, ϕ

ψ)] → K(t, ψ)}

Nozick's strategy is to use his analysis of knowledge to show why this closureprinciple is false. Showing this, he will have blocked the sceptic's argumentby way of refuting the general principle which provides the justification forthat argument's premiss (1). Can Nozick show that closure fails withoutassuming that the actual world is not a sceptical world? If so, then Craig'scharge will be answered: Nozick's analysis will be seen to be potent againstthe sceptic without being redundant.2




Since the closure principle is presumably meant to have the status of aconceptual truth about knowledge, the principle is false if the following ispossible for some knower u and some propositions Q and R:

• K(u, Q) & K(u, Q

R) & ∼K(u, R)

Using Craig's example, let us show that it is ‘perfectly possible for (A) “Mooreknows that he has hands” to be true when (B) “Moore knows that he is notin a sceptical world being deceived into thinking that he has hands” is false’.Craig claims that this can be shown using Nozick's analysis only if we assumethat the actual world is not a sceptical world. This claim is mistaken.

Consider Moore inhabiting a world w which is distinct from the actual worldand which is very similar in character to my representation of the actualworld (which representation may well fail to accurately represent the actualworld, for all I know). Suppose then that w is not a sceptical world and thatMoore correctly believes in w that Q—that he has hands. In the ∼Q‐worldsclose to w, Moore does not mistakenly believe that Q. In these worlds (whichare also not sceptical worlds), Moore has, for example, suffered a terribleaccident, and he does not mistakenly believe that he has hands. So Mooresatisfies the first of Nozick's subjunctive conditions for knowing that Q. Hesatisfies the second as well, let us suppose: in the Q‐worlds close to w, Moorecorrectly believes that Q, since in these non‐sceptical worlds, Moore hashands and perceives that he does in the normal way. So Moore knows thatQ, on Nozick's analysis. Let us suppose that Moore knows that Q entails R—the proposition that Moore is not in a sceptical world being deceived intothinking that he has hands.3 Finally, we can complete the example by notingthat Moore does not satisfy Nozick's first subjunctive condition with respectto R, since the ∼R‐worlds close to w are sceptical worlds (p. 308 ) in whichMoore mistakenly believes that R: in these sceptical worlds, he believes thathe is not in a sceptical world. So Moore does not know that R, on Nozick'sanalysis.

Thus we have a counterexample to closure. We have shown that it isperfectly possible for ‘Moore knows that he has hands’ to be true when‘Moore knows that he is not in a sceptical world . . .’ is false. Constructionof the counterexample to closure does not depend on any assumptionconcerning the character of the actual world, since the example concernsa world w distinct from the actual world and, for all we know, possibly quite




dissimilar to the actual world. In particular, we need nowhere assume thatthe actual world is not a sceptical world, contrary to what Craig charged.

To return to the sceptical argument, we now see that when the anti‐sceptic asks for some reason to accept premiss (1) of that argument, thesceptic can no longer appeal to the closure principle as a true, unrestrictedgeneralization about knowledge, one of whose instances is (1). Maybe thesceptic can defend (1) against Nozick by putting forward some restrictedclosure principle, in particular, some principle which is not falsified by theforegoing example and which entails (1) as an instance.

The counterexample to closure was carefully chosen. Let us specifyits crucial feature. Consider a knower who allegedly constitutes acounterexample to closure in virtue of knowing an entailing proposition whilefailing to know an entailed proposition (and recognizing the entailment).Call the worlds which are close to the knower's world and which are worldswhere the entailing proposition is false: false antecedent worlds. Call theworlds which are close to the knower's world and which are worlds where theentailed proposition is false: false consequent worlds. In the above exampleconcerning Moore, the false antecedent worlds are very far from (verydissimilar to) the false consequent worlds. This allows the circumstance thatthe knower (i) tracks the truth value of the entailing proposition through thefalse antecedent worlds (so he satisfies Nozick's first subjunctive conditionfor knowing the entailing proposition) but (ii) fails to track the truth value ofthe entailed proposition through the false consequent worlds (so he fails tosatisfy the first subjunctive condition for knowing the entailed proposition).

This suggests that the sceptic might resist the force of Nozick's attack byrestricting the closure principle he asserts in the following way: the entailingϕ and the entailed ψ must be such that the false antecedent worlds aresufficiently close to (similar to) the false consequent worlds.4 But then thesceptic runs into the same sort of difficulty which Craig tried to pin on theanti‐sceptic Nozick: in order to use the restricted closure principle to justifypremiss (1) of the sceptical argument, the sceptic needs to be in a positionto assert that (p. 309 ) the actual world is a sceptical world. This is because(1) follows from the restricted closure principle only if the pertinent falseantecedent worlds are sufficiently close to (similar to) the pertinent falseconsequent worlds. The latter worlds are SK‐worlds. Thus the former worlds—the worlds close to the actual world in which I am not sitting—would haveto be SK‐worlds as well. Non‐sceptical worlds would presumably not count assufficiently close to SK‐worlds.




In conclusion, when Nozick's anti‐sceptical strategy is seen aright, it is seento be immune to Craig's charge. The envisioned sceptical response to Nozick(restricting closure) lands the sceptic in the same sort of difficulty Craig laidat Nozick's door.

Notes:

(1) Craig (1989: 161–2).

(2) Even though Craig's criticism of Nozick is unsuccessful, I believe thatNozick's anti‐sceptical strategy has other problems. See Brueckner (1984c:259–64).

(3) There are difficulties in applying Nozick's first subjunctive condition toone's belief of a necessary proposition. Let us waive these problems, sincethey are not the focus of Craig's objection to Nozick.

(4) This restriction would need to be sharpened, but I am arguing that it is onthe wrong track anyway.


http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199585861.001.0001/acprof-9780199585861-bibliography-1#acprof-9780199585861-bibItem-102

http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199585861.001.0001/acprof-9780199585861-bibliography-1#acprof-9780199585861-bibItem-54

Documents

Unfair to Nozick