This article offers a critique of Thomas Scanlon's well-known account of promissory obligation by reference to the rights of promisees. Scanlon's account invokes a moral principle, the "principle of fidelity". Now, corresponding to a promisor's obligation to perform is a promisee's right to performance. It is argued that one cannot account for this right in terms of Scanlon's principle. This is so in spite of a clause in the principle relating to the promisee's "consent", which might have been thought to (...) do the trick. Most likely this argument can be applied to all "moral principle" accounts of promissory obligation. An alternative both to these and to "social practice" accounts is needed. (shrink)