Abstract

Many epistemologists have been attracted to the view that knowledge-wh can be reduced to knowledge-that. An important challenge to this, presented by Jonathan Schaffer, is the problem of “convergent knowledge”: reductive accounts imply that any two knowledge-wh ascriptions with identical true answers to the questions embedded in their wh-clauses are materially equivalent, but according to Schaffer, there are counterexamples to this equivalence. Parallel to this, Schaffer has presented a very similar argument against binary accounts of knowledge, and thereby in favour of his alternative contrastive account, relying on similar examples of apparently inequivalent knowledge ascriptions, which binary accounts treat as equivalent. In this article, I develop a unified diagnosis and solution to these problems for the reductive and binary accounts, based on a general theory of knowledge ascriptions that embed presuppositional expressions. All of Schaffer's apparent counterexamples embed presuppositional expressions, and once the effect of these is taken into account, it becomes apparent that the counterexamples depend on an illicit equivocation of contexts. Since epistemologists often rely on knowledge ascriptions that embed presuppositional expressions, the general theory of them presented here will have ramifications beyond defusing Schaffer's argument.