The Evidence-condition

If the argument of the previous chapter was correct, then ‘A knows that p’ entails ‘A truly believes that p’. But true belief does not entail knowledge. The latter point is made by Plato in the Theaetetus 200D–201C). It may be illustrated, for instance, by The Case of the Optimistic Punter. Because he is optimistic, he regularly believes that the horses he bets on will win. But he never has any reliable information about these horses. As a result, he normally loses. From time to time, however, his horses win. On such occasions his beliefs are true. But we do not think that he knows that these horses will win.

This is the occasion for introducing the Evidence-condition. The trouble about the punter, it is plausibly suggested, is that he lacks good reasons or sufficient evidence for his true belief. If only he had that, he would know.

However, when the Evidence-condition is scrutinized more closely, all sorts of problems emerge. In this section no less than five subconditions will be outlined which the Evidence-condition must satisfy, if it is accepted at all. All these sub-conditions raise important problems.

Condition 1. Suppose that p is true, A believes that p and A has evidence for ‘p’, namely ‘q’. It cannot be the case that A knows that p unless, as a matter of objective fact, ‘q’ constitutes sufficient evidence to establish the truth of ‘p’ It will be argued at a later point (Chapter Fourteen, Section One) that, for knowledge, such ‘sufficient evidence’ must be conclusive evidence.