Conformity by an agent to a convention to which the agent is a party is rational only if the agent prefers to conform given the other parties conform and believes the others will conform. But this justification is inadequate; what, for example, is the justification for this belief? The required rational justification requires recourse to (a) preferences for general conformity (as opposed to merely conditional preferences for one's own conformity) and (b) procedures. An agent adopts a procedure when he chooses to perform a whole set of future actions, as opposed to a single action.
Conventions play a crucial role in human societies. Human language is conventional, as are monetary systems, methods of eating, and modes of dress. This suggests that conformity to conventions is, at least for the most part, a species of rational activity. In this paper I want to try to provide a rational justification for conformity to conventions.
An action, x, is prima facie rational if an agent, A, has a preference for some state of affairs, S1, and believes that performing x will bring about S1. He prefers the action x to, say, the action y, if x-ing will bring about S1 but y-ing will not.
Two types of preference can be distinguished here. First, there is A's unconditional preference for the state of affairs S1 over another state of affairs $2. Second, there is A's conditional preference for x-ing over y-ing. A's preference for x is conditional on x bringing about $1. Presumably many agents have many preferences which are not dependent on the actions or preferences of Others. However, some preferences are in this way dependent. In particular, agents involved in collective enterprises prefer to perform their contributory actions on the condition that others perform theirs. For example, it might be the case that agent A is willing to go to battle against a common enemy only if his neighbours B and C are likewise willing. In such a situation A prefers to x (go to battle) on condition B and C x. This preference is conditional. I suggest that conventions involve interdependence of action, a Agents conform on condition others conform. In that case agents prefer to conform on the condition that others conform; conventions, then, involve conditional preferences. But if convention followers