 According to Bolzano’s definition, deducibility requires compatibility. This gives rise to some complications, e.g., deducibility is not reflexive, and from the fact that \(B\) is deducible from \(A\) with respect to \(i, j, \ldots\) we can conclude that not-\(A\) is deducible from not-\(B\) only if \(B\) is not universally valid with respect to \(i, j, \ldots.\) But it also brings an important benefit, namely, it allows him to integrate a relation of relative probability directly into his system. In TS, § 161, he defines the conditional probability (or relative validity) of a proposition M(i) with respect to a class of premises or hypotheses A(i) with variables i, as the ratio of the number of cases in which all the propositions of the class as well as M(i) are true to the number of cases in which the propositions A(i) are all true. In other words, it is the ratio of the number of true variants of A(i) and M(i) to the number of true variants of A(i). Bolzano’s conditional probability is objective, an sich. 