Wednesday, July 09, 2008


DeRose on the Tracking Account

While reading back through Keith DeRose's fantastic 'Solving the Skeptical Problem', I came across a claim that I'd previously taken on trust from DeRose, but which came to seem quite puzzling in conversation with John Bengson. In a footnote, DeRose writes:

'I've skipped entirely Nozick's fourth condition, but I believe this fourth condition to be redundant, anyway: It automatically holds whenever true belief is present.' (27fn27)

Now, this redundancy claim might be encouraged by Nozick's presentation of the four conditions of his tracking account of knowledge:

S knows that p iff:

(1) p is true
(2) S believes that p
(3) ~(1) -> not ~(2)
(4) (1) -> (2),

where -> is a subjective conditional, rather than an indicative condition.

But this bare-bones presentation of the account isn't very helpful, and we have to look to Nozick's surrounding discussion to fill it out a bit. What's suggested is that condition (4) should be understood like this:

Were it, in changed circumstances, still the case that p, S would still believe that p.
(Adapted from Wright's 'Keeping Track of Nozick': 135. Wright ignores the needed relativization to methods, and for the purposes of this post I can afford to follow.)

Now, my question is this; why does DeRose think that this condition is redundant given conditions (1) and (2)? For that matter, why isn't the example Nozick used to motivate (4) a counterexample to DeRose's claim that (4) 'automatically holds whenever true belief is present'?

Nozick asks us to imagine a poor envatted subject having his brain manipulated by scientists so that he comes to believe that he is envatted and that scientists are inducing beliefs in him by manipulating his brain. He has a true belief that he's envatted and that scientists are inducing beliefs in him by manipulating his brain. But does this belief satisfy (4)? Nozick argues it doesn't:

'The person in the tank does not satify the subjunctive condition 4. [...] It is not true of him that if he were in the tank he would believe it; for in the close world (or situation) to his own where he is in the tank but they don't give him the belief that he is (much less instill the belief that he isn't) he doesn't believe he is in the tank. Of the person actually in the tank and believing it, it is not true to make the further statement that if he were in the tank he would believe it - so he does not know he is in the tank.'

Even leaving aside Nozick's final claim that the person in the tank doesn't know that they are, the example is a little hard to evaluate since, as usual, claims about the relative closeness of worlds are always somewhat slippery. But it seems plausible enough, and there seem to be other examples of this form readily available. For instance, Nozick mentions Harman's case of the guy who reads about the death of the dictator of his country, but fails to be exposed to the massive cover-up that follows. Structurally similar examples seem to abound.

Any thoughts on what DeRose had in mind? And does the point stand or fall with an analogous complaint against safety (S believes that p -> p)?


I'm just speculating, but my guess is that DeRose is assuming something like the standard Lewis-Stalnaker semantics for counterfactuals. On this kind of semantics, it is a theorem that (A & B) entails (A []-> B.) If the actual world is an A-world, then the actual world is the closest A-world; if it's also a B-world, then all the closest A-worlds are B-worlds.

Nozick, by contrast, is employing a nonstandard account of counterfactuals, according to which not only the closest A-worlds are relevant, but where all the *close* A-worlds are.

You're right that just this issue carries over into discussions of Sosa-style safety, too.
Thanks for the kind words about my paper!

Jonathan is right: In SSP I was assuming that A[]-->B is true whenever A and B are both true. So I was disagreeing with Nozick's claim that "it is not true to make the further statement that if [the guy in the tank] were in the tank he would believe it."

I changed my stance on that issue in a later paper -- "Sosa, Safety, Sensitivity, and Skeptical Hypotheses," SOSA AND HIS CRITICS, 2004; pre-publication draft available in word & pdf at my list of on-line papers:
I still think Nozick (& Sosa, too) suffers from "the problem of true/true subjunctives," explained in sect. 5 of the Sosa paper, but I no longer assume the "standard" view that true-true subjunctives are all true. Rather, I go through multiple approaches to true-true subjunctives and then try to assess how promising the relevant conditions of Nozick's and Sosa's are.
Thanks for the helpful responses. It's been a while since I looked at the relevant material on counterfactuals, and my rustiness is clearly showing. I guess what struck me was that while stating the condition as ~p []-> ~Bp doesn't rule out the actual world, the gloss from Crispin explicitly does (I'm thinking of the 'in changed circumstances' clause).
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