In this article I argue that two received accounts of belief and assertion cannot both be correct, because they entail mutually contradictory claims about Moore’s Paradox. The two accounts in question are, first, the Action Theory of Belief (ATB), the functionalist view that belief must be manifested in dispositions to act, and second, the Belief Account of Assertion (BAA), the Gricean view that an asserter must present himself as believing what he asserts. It is generally accepted also that Moorean assertions are absurd, and that BAA explains why they are. I shall argue that ATB implies that some Moorean assertions are, in some fairly ordinary contexts, well justified. Thus BAA and ATB are mutually inconsistent. In the concluding section I explore three possible ways of responding to the dilemma, and what implications they have for the nature of the constitutive relationships linking belief, assent and behavioural dispositions.