Promises and Expectations

We investigate why people keep their promises in the absence of external enforce-ment mechanisms and reputational e¤ects. In a controlled laboratory experiment we show that exogenous variation of second-order expectations (promisorsexpectations about promisees expectations that the promise will be kept) leads to a signi\u85cant change in promisor behavior. We provide clean evidence that a promisors aversion to disappoint a promisees expectation leads her to keep her promise. We propose a simple theory of lexicographic promise keeping that is supported by our results and nests the \u85ndings of previous contributions as special cases