Abstract

Some recent epistemologists propose that certainty is the norm of action and assertion. This proposal is subject to skeptical worries. If, as is usually supposed, certainty is very hard to come by, legitimate action and assertion will be rare. To remedy this, some have conjoined their certainty-norms with a context-sensitive semantics for ‘certainty’. For a proposition to be certain for you, you only need to be able to exclude relevant alternatives. I argue that, depending on what makes an alternative relevant, this kind of view is disingenuous. In particular, if an alternative can be made relevant by being relevant to rational action, it allows an escape from the skeptical consequences only by licensing David Lewis-style utterances of the form, “You know that p only if there is no probability, no matter how small, that not-p—Psst!—Unless that probability is really small.” While there are legitimate ways to exclude some possibilities from relevance, it is disingenuous, I argue, to exclude possibilities from relevance on the basis of the very characteristic—low but nonzero probability—that is claimed to be incompatible with certainty.