In Probabilismo (1931) de Finetti sketched a subjectivist treatment of the discourse of objective chance. Possible chances were to be taken as degrees of belief conditional on a specification of the chance set up, and the individuation of the chance set up was to be chosen with a certain kind of stability in mind. These leading ideas can be given a natural development using the notions of probability conditional on a partition or sigma algebra, and using the ergodic decomposition of invariant measures. The resulting theory casts some light on the nature of principles relating degree-of-belief and chance.