Nicod's criterion

A condition governing the confirmation of a general hypothesis by particular pieces of evidence, proposed by the French philosopher Jean Nicod (1893–1924) in his Foundations of Geometry and Induction (1930). It requires that an instance of a generalization that all As are B provides a positive, confirming piece of evidence for the generalization; evidence of something that is neither A nor B is irrelevant to it, as is evidence of something that is B but not A. The principle is put under pressure by Hempel's paradox, which apparently yields circumstances in which something that is neither A nor B may confirm the generalization.