From "plausibilities of plausibilities" to state-assignment methods. I. "Plausibilities of plausibilities": an approach through circumstances

This is the first part of a three-note study which starts from an analysis of "probabilities of probabilities" to arrive at old and new state-assignment methods in classical and quantum mechanics. In this note, probability-like parameters appearing in some statistical models, and their prior distributions, are reinterpreted through the notion of 'circumstance'. The idea is basically Laplace's and Jaynes', and rests on a theorem from probability theory which shows that a set of propositions can be uniquely parametrised by probability distributions. This parametrisation is invariant with respect to changes in the probabilities of the propositions themselves