Giving one’s word that one will do something creates a reason for doing it in the future. But when the time comes, by keeping the promise one seems to act because one has done something in the past, rather than for the sake of promoting some goal in the future. Promising therefore excites philosophical theory in two ways. There is first the question of the obligation to obey a promise: how can this exist, given its backwards-looking nature, and what are its stringency and limits? Secondly, there is a peculiarity about the origin of promise-making, in that it can easily seem that in a society with no such institution, it would never arise. This would be because it is essential to promising that at a later date you may have to turn aside from your own interests in order to keep the promise, and an individual who does this is relatively disadvantaged compared to one who does not. The problem is seen clearly by Hobbes. It is dramatized in the situation of the prisoners’ dilemma, where making a promise to the other prisoner that you will not cheat would seem to be an empty charade, for no words alter the penalties and rewards. The social solution, discovered by Hume, is that promising is an institution or system whereby we voluntarily attach penalties to failing to do what we have said we would do, thereby cementing our interest in doing it, and giving others increased confidence that we will, since they have a right to sanction us if we do not. It therefore enables social cooperation to flourish. See also convention, social contract.