 Probability, for Lewis, concerns a logical relation between a conclusion and premises, and a statement is categorically assertable with a degree of probability or credibility, or a belief warranted or credible to that degree, as opposed to being merely hypothetically probable a priori to that degree on premises, only to the extent that the premises or data are sufficiently credible or warranted or probable. (Lewis 1946, 315–27). Ultimately, the conclusion must be warranted or credible or probable on premises or data that are certain, not just true, and that are not just warranted or credible only on other premises or data, even if we may never reach these ultimate premises ordinarily in showing probability or justification. Otherwise we have “an indefinite regress of the merely probable...and the probability will fail to be genuine” (Lewis 1946, 186). Here he echoes MWO where he says that the validity of a probability judgement is a relation between the judgement and “ultimate premises” that (a) “may verbally be quite remote”, unlike the “immediate premises” we might initially and normally cite, that (b) must be a “certainty” rather than merely probable on yet further premises, and that (c) must be “actual given data for the individual” (Lewis 1929, 328–9). Lewis is defending a normative standard for empirical knowledge that he thinks is implicit in cognition and revealed on reflection but which is also psychologically and verbally remote from everyday cognitive practices of justifying beliefs to ourselves or others in the light of more proximate assumptions taken for granted in the context of inquiry or discussion. Some pragmatists might feel there is tension here. 