When we engage in discursive thought and declarative speech, we may attain various forms of success: intelligibility, precision, correctness, and so on. These felicities are best explained by contrast with the corresponding mishaps that threaten our beliefs, assertions, and especially our claims to know something. A person's thinking may be inadequate because he is ignorant, and what he says may be deficient because it is incoherent, rough, or, perhaps most important of all, downright false.

Many philosophers have been troubled in attempting to account for the occurrence of falsity in people's assertions and opinions, that is, in trying to understand how there could be such a thing as error at all. In examining these difficulties, we shall assume a man's statement is erroneous in case it is false and it reflects his belief. Thus, if a man lies, he may speak falsely, but not erroneously. We shall also...