What Is It to “Believe” Something?

To understand the role of beliefs in generating action, we have to understand their nature, their causes, and their consequences. As I mentioned in the introductory remarks to Part II, it is not always clear what it means to “believe” that something is the case, for example, that there is a life after death. Many of the great religious figures have written about their constant struggle with doubt. In their believing moments, was their faith as simple and unconditional as that of someone who has never known doubt? Did the followers of Communism who “believed” that the party can do no wrong really believe it? How can we tell the difference between the congenital pessimist who tends to believe the worst and the prudent decision maker who merely acts as if the worst-case scenario were true?

Also, in everyday language “belief ” suggests less than full endorsement. I believe it will rain tomorrow, but I also know I might be wrong. I do not merely believe that I am married; I know it. In philosophical analyses, knowledge is usually defined as justified true belief, a belief that stands in a particular relation both to the world (it is true) and to the body of evidence the agent possesses (it is justified). Yet neither of these features of knowledge captures the subjective certainty that often underlies the phrase “I know” in ordinary discourse.