 Lewis’ response is instructive for his understanding of epistemology. For Lewis (1952a, reprinted in Lewis 1970, 330), a principal task of epistemology is with the “validity” of knowledge, that is to say with the justification or warrant for cognition that distinguishes empirically warranted belief from lucky or unlucky guess or hazard of belief. If a class of beliefs in principle may be false, we need some reason or grounds for thinking its members true or likely to be true, especially if we plan to base other beliefs on them. That requires present or past justifying grounds of belief, not just future potential for verification or confirmation as he thinks Goodman proposes. Otherwise, we confuse justification with verification, or ignore the former for the latter. Nor can the grounds consist solely in other beliefs that might be mistaken without grounds for thinking them true or likely to be true, or in beliefs that stand in conditional probabilistic relations to each other, as he thinks Reichenbach proposes, without any antecedent probabilities deriving from something else (Lewis 1952a, reprinted in Lewis 1970, 328). Lewis acknowledges that his (somewhat traditional) concerns with validation or justification, skepticism, and the need for given justifying grounds, lead him to depart from or supplement standard pragmatic theories. 