In the first four chapters I have been claiming that skeptical arguments play an important role in philosophical inquiry. Such arguments act as heuristic devices for driving positive epistemology in particular, as opposed to ontology or philosophy of mind. I mean this thesis to be both prescriptive and descriptive. On the one hand, I am claiming that skeptical arguments ought to play this methodological role. On the other, the claim is that such arguments do in fact play it. Nothing supports the descriptive thesis more than the literature on the skeptical argument from an infinite regress of reasons. That argument is beautifully simple, but it has inspired debate over the nature of knowledge and evidence for over two millennia.

THE REGRESS ARGUMENT AND STRONG PARTICULARISM

The problem arises because it seems that one must have good reasons for whatever one claims to know. But not any reason is a good reason; one must have reasons for thinking that one's reasons are true. Accordingly, it seems that knowledge requires (per impossibile) an infinite regress of reasons. An early version of the argument is attributed to the ancient skeptic, Pyrrho. The passage quoted next is taken from Sextus Empiricus's discussion of Agrippa's five skeptical modes leading to the suspension of judgment. Agrippa, in turn, was systemizing the skeptical teachings of Pyrrho.