The power to promise is morally fundamental and does not, at its foundation, derive from moral principles that govern our use of conventions. Of course, many features of promising have conventional components—including which words, gestures, or conditions of silence create commitments. What is really at issue between conventionalists and nonconventionalists is whether the basic moral relation of promissory commitment derives from the moral principles that govern our use of social conventions.
Other nonconventionalist accounts make problematic concessions to the conventionalist's core instincts, including embracing: the view that binding promises must involve the promisee's belief that performance will occur; the view that through the promise, the promisee and promisor create a shared end; and the tendency to take promises between strangers, rather than intimates, as the prototypes to which a satisfactory account must answer.
I argue against these positions and then pursue an account that finds its motivation in their rejection. My main claim is: the power to make promises, and other related forms of commitment, is an integral part of the ability to engage in special relationships in a morally good way. The argument proceeds by examining what would be missing, morally, from intimate relationships if we lacked this power.