The term „probability” in Newman’s philosophy is ambiguous. This fact, very often causes the chaos of interpretation. The second difficulty is to grasp the relationship between the probability and certainty-certitude in the system of its thought. The aim of this article is to try to solve these two matters. The way of using the word by the cardinal shows that it is an instrument of implicit reasoning and it has an epistemic meaning. The accumulation of probabilities brings us to assent something as the truth. However, they never extort for it. When in the province of implicit reasoning the assent is the fact, and is reflected upon, then the assent is the certitude. So, in Newman’s thought probability is a natural way to certitude.The term „...