The strategic structure of promise keeping is quite varied, with three distinct kinds (Hardin 1988b, 59–65). First, there are promises made without any reciprocal benefit to the promiser, whose fulfillment is essentially altruistic. Such promises are commonly called gratuitous, and in some societies there is law to govern these while in others there is little or none (Dawson 1980). Second, there are coordination promises, which do little more than coordinate joint actions at future times, as in our mutual promise to meet for lunch tomorrow. Finally, there are exchange promises, which are explicitly a reciprocal part of an exchange relation. In a case of the latter, for example, you may do something for me now in return for my promise to do something for you later.

DEFINE: Distinguishes gratuitous, coordination, and exchange promises as a taxonomy.

Russell Hardin, Trust and Trustworthiness, loc. 326