In his book, Philosophical Explanations, in the chapter “Knowledge and Skepticism,” Robert Nozick endeavors to construct a set of conditions that are jointly sufficient for knowledge. Let’s call this the ‘truth-tracking’ account of knowledge. Truth-tracking is meant to deal with a range of hard epistemological cases, including Getter-style problems and Brain-in-the-Vat-style skeptical arguments. In this paper, I aim to show that, while Nozick’s truth-tracking account doesn’t succeed as a whole (largely for reasons noted by Saul Kripke), the driving intuition of Nozick’s account may still be relevant to – or even necessary for – any good theory of knowledge. I will refer to this driving intuition as ‘Sensitivity.’ Precisely what I mean by this term will become clearer as we go along.
PART I: Truth-tracking Explained
Nozick begins his project by taking for granted the usual first two conditions for knowledge: (1) p is true; (2) S believes that p. I’ll take these for granted as well. To these he adds a third condition, the subjunctive conditional: (3) If p weren’t true, S wouldn’t believe that p. We may also express this as: ~p□→~SBp.1 I will, however, use such formalisms sparingly, because I want to be semantically clear about what I’m referring to. Nozick also uses ‘closest possible worlds’ semantics to express (3), though is not entirely committed to them.2 I will, however, make use of these. For example: S’s belief should be counterfactually sensitive so that, in the closest worlds where not-p, S wouldst mistakenly believe that p. Note that (3) is the heart of Sensitivity, though it doesn’t capture the whole truth-tracking account. To develop that, let’s apply our conditions thus far to some classic hard cases. Continue Reading