Since Plato’s Theaetetus there has been a tradition of defining knowledge as true belief plus a logos or reason. In the most familiar form, knowledge is justified true belief. In 1963 the American philosopher Edmund Gettier provided a range of counterexamples to this formula. In his cases a belief is true, and the agent is justified in believing it. But the justification does not relate to the truth of the belief in the right way, so that it is relatively accidental, or a matter of luck, that the belief is true. For example, I see what I reasonably and justifiably take to be an event of your receiving a bottle of whisky and on this basis I believe you drink whisky. The truth is that you do drink whisky, but on this occasion you were in fact taking delivery of a medical specimen. In such a case my belief is true and justified, but I do not thereby know that you drink whisky, since this truth is only accidental relative to my evidence. The counterexamples sparked a prolonged debate over the kinds of condition that might be substituted to give a better account of knowledge, or whether all suggestions would meet similar problems. See also no false lemmas principle.