Abstract

Two standard probabilistic theories of evidence are introduced: increase‐in‐probability (positive relevance) and high‐probability. These theories must be augmented by some definition of probability if a full theory of evidence is to be formulated and evaluated. Four popular theories of probability are presented: Carnap's _a priori_ theory, the frequency theory, the propensity theory, and the subjective theory. It is shown how each yields a different concept of evidence.