Nozick, Knowledge and scepticism
Knowledge as tracking the truth
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Nozick’s key idea that to know that P is to have a belief that P which tracks the
truth that P.
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Nozick’s analysis of knowledge. S knows that P iff (i) P is true; (ii) S believes
that P; (iii) S would not believe P were P not true; and (iv) S would believe P were
P true.
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To have a belief that P which tracks the truth that P is to have a belief that P
which is sensitive to how the world really is.
Notice that Nozick’s account in no way appeals to justification.
Nozick’s analysis nicely handles a variety of puzzling cases:
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Gettier cases. Because of (iii), Smith doesn’t know that the man who will get
the job has ten coins in his pocket because he would still believe it were it not
true that the man who will get the job has ten coins in his pocket.
Fake barn example. Because of (iii), Henry doesn’t know that he’s seeing a
barn because he would still believe it was a barn were it in fact papier-mâché.
Brain in a vat case. Because of (iv), the brain in a vat doesn’t know that
he’s a brain in a vat because he would not believe he is a brain in a vat were it
true that he was.
Dictator case. Because of (iv), the first edition reader doesn’t know the
dictator is dead because he would not believe it were it true.
Response to skepticism
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To respond to the skeptic, we needn’t convince the skeptic that they are wrong. It
is enough to convince ourselves not to take the skeptical possibility to undermine
the possibility of knowledge.
Consider some skeptical possibility SK (I am dreaming).
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I know that SK is false iff (i) SK is false; I believe that SK is false; (iii) I
wouldn’t believe SK is false were SK true; and (iv) I would believe SK is false
were SK false.
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But focus on (iii): were SK true, I would still believe that SK is false.
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So, I don’t know that SK is false.
Consider the following skeptical argument:
BTK 09:
Nozick
(1 of 2)
Week 3
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Skeptical Possibility. I don’t know that not-SK.
Closure. If I don’t know that not-SK, then I don’t know what I
ordinarily believe.
Conclusion. Therefore, I don’t know what I ordinarily believe.
Closure needs to be broken down into several bits:
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Consider the following “closure” principle:
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Notice that this is equivalent to its contrapositive principle:
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If I don’t know that Q, then either I don’t know that P or I don’t know that
P entails Q.
The Closure premise is an instance of the latter:
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If (i) I know that P and (ii) I know that P entails Q, then I know that Q.
If I don’t know that not-SK, then either I don’t know what I ordinarily
believe or I don’t know that not-SK entails that my ordinary beliefs are
false.
It is assumed that I do know that not-SK entails that my ordinary beliefs
are false.
Simplifying, we get the Closure premise: if I don’t know that not-SK
obtains, then I don’t know what I ordinarily believe.
Nozick believes the Closure premise is false.
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Counterexample. That I am in New York entails that I am not a brain in a
vat on Alpha Centauri. I know that I am in New York. I do not know that I
am a brain in a vat on Alpha Centauri. So, Closure fails.
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This is because (iii) is not closed under logical implication:
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I would not believe that I am in New York were I not in New York. But
it is false that I would not believe that I am somewhere were I not in
New York.
Kripke’s objection to Nozick. Suppose that all but a few of the red barns in
the countryside have burned down. The locals replace them with papier-mâché
facades which are not red. Henry, driving through, sees one of the few real red
barns. He believes he sees a barn and that he sees a red barn.
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But… on Nozick’s view, Henry’s belief that he sees a red barn tracks the
truth, but not his belief that he sees a barn (he would still believe he sees a
barn, even if he weren’t seeing one but seeing the facades instead).
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BTK 09:
So, Nozick’s view absurdly predicts that Henry knows that he sees a red
barn but does not know that he sees a barn.
Nozick
(2 of 2)
Week 3