Criteria of knowledge and wimpy skeptics

Sextus Empiricus seems to argue that there can be no rationally defensible criterion for what counts as knowledge, since any criterion would need a demonstration of its authoritative standing as a criterion, and such a demonstration would have to presuppose another criterion as its basis of justification.

Thus he comes to the uncomfortable position of claiming, as something known, that there can be no rationally defensible criterion of knowledge. In some passages he tries to weasel out of this consequence by describing skepticism as a mere attitude of non-commitment, rather than a judgement about something known. This wimpy version of skepticism wouldn't get him very far, however, for if skepticism is nothing more than an attitude, why should anyone else care?

Other passages suggest that Sextus wants to claim something stronger, that the skeptic doubts everything that is not evident. This leaves him free to assent to knowledge of appearances (that things appear as they appear we need not doubt), and to (deductive) inferences from those evident things by means of logically evident rules (like the excluded middle). On this view of skepticsm, the argument against the criterion yields evident knowledge -- that there is no criterion for non-evident knowledge.

If this reading is right, Sextus begins to look like the image of Hume that emerged from the Enquiry -- rejecting all induction, and restricting reason to the a priori. Perhaps this clarifies what seemed mystifying about Hume's view.