One approach to understanding ‘reasons’ – including both reasons for action and reasons for belief – postulates a fundamental connection between reasons and reasoning. According to this approach, there is a reason for you to φ – where φ-ing could be either an action (such as writing a letter) or an attitude (such as believing that it is snowing) – if and only if there is a possible process of sound or rational reasoning that could take you from your current state of mind to your rationally φ-ing.

This approach is familiar in discussions of reasons for action. As Bernard Williams (1995: 35) put it, for there to be a reason for you to φ, there must be a ‘sound deliberative route’ that leads from your current state of mind to your being motivated to φ. Presumably, Williams's reference to ‘a sound deliberative route’ comes to more or less the same thing as my own terminology of a ‘possible process of rational reasoning’.

It is clearly possible to take the same approach to understanding reasons for belief. You have a reason to believe p if and only if there is some possible process of rational reasoning that could lead you from your current state of mind to your being rationally inclined to believe p. So one way to make progress in understanding reasons for belief is to investigate which processes of reasoning count as rational.