 Bolzano adds proofs of a number of standard theorems, and also defines subjective probability and different important probabilistic notions such as the degree of confidence, the credibility of a witness, etc. He gives the formula of the degree of credibility of an event reported by independent testimonies as a function of the number of witnesses, of the number of testimonies, and of the number of true and false propositions stated by each witness. All these concepts play an important role in the chapter “on the nature of historical knowledge, particularly concerning miracles” in Bolzano 1834.