 A set of beliefs is congruent for Lewis (1946, 338) when the antecedent probability of each is increased by the assumption of the truth of the rest. A physical object statement \(P\) and the set of sensory conditionals that constitute its content form a congruent set, as we have seen. Indeed, by virtue of exhausting the empirical content of \(P\), Lewis (1946, 348–9, footnote 6) thinks the sensory conditionals constitute a congruent set by themselves. In any case, the degree of warrant enjoyed by the various elements of a mature system of empirical belief, especially one that counts as knowledge, depends on the inferential support the elements provide each other and the total empirical and memorial data present. However, Lewis emphasizes that for the members of a congruent system to have any degree of probability, “it is absolutely requisite that some at least of the set of statements possess a degree of credibility antecedent to and independent of the remainder of those in question, and derivable from the relation of them to direct experience” (Lewis 1946, 339).