In their forthcoming—and I must say excellent—paper “Knowledge and Action”, John Hawthorne and Jason Stanley defend the following principle:

The Reason-Knowledge Principle (roughly)

Where one’s choice is p-dependent, it is appropriate to treat the proposition that p as a reason for acting iff you know that p.[1]

Importantly, Hawthorne and Stanley say that this principle is to be situated within a decision-theoretic framework according to which knowledge that p requires credence 1 in p. The reason is somewhat obvious: if it is possible to know that p without having credence 1 that p, then any plausible decision theory will predict that there are cases where it is *not* appropriate to treat the proposition that p as a reason for acting even though one knows that p. In any case where the expected value/utility of A is greater than that of B, but the expected value/utility *conditional on p* of B is greater than that of A, it is inappropriate to treat p as a reason. In such a case, treating p as a reason would presumably require preferring B to A, which contradicts standard decision theory. On the other hand, if one’s credence in p is 1, then it cannot be the case that the expected value/utility of A is greater than B and vice versa for the conditional-on-p expected values/utilities of A and B. Hence, Hawthorne and Stanley require that knowledge that p requires credence 1 that p, thereby blocking any such cases.

This raises an obvious objection, an objection which Hawthorne and Stanley explicitly consider: