Is Justified True Belief Knowledge?
Edmund L. Gettier NOTE: Originally published in Analysis 23 (1963), pp. 121-3 (Oxford, Blackwell Publishers, 1963). Various attempts have been made in recent years to state necessary and sufficient conditions for someone’s knowing a given proposition. The attempts have often been such that they can be stated in a form similar to the following:1 (a) S knows that P IFF (i) P is true, (ii) S believes that P, and (iii) S is justified in believing that P. For example, Chisholm has held that the following gives the necessary and sufficient conditions for knowledge:2 (b) S knows that P IFF (i) S accepts P, (ii) S has adequate evidence for P, and (iii) P is true. Ayer has stated the necessary and sufficient conditions for knowledge as follows:3 (c) S knows that P IFF (i) P is true, (ii) S is sure that P is true, and (iii) S has the right to be sure that P is true. I shall argue that (a) is false in that the conditions stated therein do not constitute a sufficient condition for the truth of the
