  On this definition, a convention prevails in a population when each member of the population plays his part in some system of actions because he perceives that it is in his interest to do so, given that others perceive it is in their interests to do so. Several features of this definition deserve emphasis. First, a convention contributes to the mutual benefit of its participants. Second, a convention need not result from explicit promise or agreement. Third, each participant believes that other participants obey the convention. Fourth, given this belief, each participant has reason to obey the convention herself. This fourth point emerges even more sharply in the Treatise: “the actions of each of us have a reference to those of the other, and are perform’d upon the supposition, that something is to be perform’d on the other part” (p. 490). Hume illustrates his approach with the memorable example of two men sitting in a row-boat. In order to move at all, they must synchronize their rowing, which they do without any explicit agreement.