Most theories of promising are insufficiently broad, for they ground promissory obligation in some external or contingent feature of the promise. In this paper, I introduce a new kind of theory. The Mental States First (MSF) theory grounds promissory obligation in something internal and essential: the mental state expressed by promising, or the state that promisors purport to be in. My defense of MSF relies on three claims. First, promising to Φ expresses that you have resolved to Φ. Second, resolving (...) to Φ commits you to Φing, all else being equal. Third, the norms on speech acts are determined by the norms on the mental states they express, such that publicly expressing that you are in a state subjects you to whatever commitments are normally incurred by being in that state, regardless of whether you really are in it. I suggest that this general approach might also explain how the norms on other sorts of speech acts work. (shrink)