WHEN is a belief rational? Why do we want our beliefs to be rational, how can we tell whether they are, and how can we improve their rationality?
Two themes permeate the philosophical literature. First, that rationality is a matter of reasons. A belief's rationality depends upon the reasons for holding that belief. These will be reasons for thinking the belief is true (or perhaps for thinking that it has some other desirable cognitive virtue, such as explanatory power). Second, that rationality is a matter of reliability. Does the process or procedure that produces (and maintains) the belief lead to a high percentage of true beliefs? A rational belief is one that arises through some process that reliably produces beliefs that are true (or that have some other desirable cognitive virtue).
Neither theme alone exhausts our notion of rationality. Reasons without reliability seem empty, reliability without reasons seems blind. In tandem these make a powerful unit, but how exactly are they related and why?
It is natural to think of rationality as a goal-directed process. (This applies to both rationality of action and rationality of belief.) The stereotype of behavior in traditional societies is that people act a certain way because things always have been done that way. In contrast, rational behavior is aimed at achieving the goals, desires, and ends that people have. On this instrumental conception, rationality consists in the effective and efficient achievement of goals, ends, and desires. About the goals themselves, an instrumental conception has little to say.* If rational procedures are ones that reliably achieve specified goals, an action is rational when it is produced by such a procedure, and a person is rational when he appropriately uses rational procedures.____________________