Abstract
The causal propensity of an event F to cause another event E is explicated as the weight of evidence against F if E does not occur, given the state of the universe just before F occurred. This definition, first given in 1961, is sharpened, defended, and applied to several examples. In this definition the concept of weight of evidence in favor of a proposition, provided by another one, is to be understood in a technical sense that is intended to capture its most customary informal meaning.