Incomplete Promises and Norm for keeping Promises

Promises, like contracts, are by definition incomplete, and subject to different interpretations by distinct parties, with their conflicting interests, and selfish whenever circumstances change and the promissory obligation is not univocal. This project studies how promisors, promisees, and neutral individuals estimate how promisors expect promises to behave, and vice-versa, and how neutral individuals assess the immorality of breaking a promise, when the promise does not explicitly address the occurred contingency. Experimental results reveal how the incompleteness of a promise and the unpredictability of the contingency affect the norm for keeping promises, leading to lower empirical and normative estimates by promisors, promisees, and neutral individuals. Promisors selfishly distort their beliefs to violate the promise, without incurring guilt or moral costs, but even neutral individuals believe that violation is more socially acceptable when the promise is incomplete. Several implications for contract law are discussed.