 What then is tested and confirmed or disconfirmed by experience is the interpretation of experience in the light of our concepts, ordinary empirical concepts like dog as well as more abstract categories like causality or the concepts of logic. What isn’t tested by experience is the validity of the concepts themselves, or the logical relationships amongst them, or the principles for applying them. Agents bring them to experience and the only criteria they answer to are pragmatic ones of utility or convenience (Lewis 1929, 271–2).That implies that they are also revisable on pragmatic grounds, as Lewis himself recognizes he is doing to some extent with the concept of knowledge itself (Lewis 1946, 27–29, 183) . 