The diachronic Bayesian

It is well known that a Bayesian probability forecast for all future observations should be a probability measure in order to satisfy a natural condition of coherence. The main topics of this paper are the evolution of the Bayesian probability measure and ways of testing its adequacy as it evolves over time. The process of testing evolving Bayesian beliefs is modelled in terms of betting, similarly to the standard Dutch book treatment of coherence. The resulting picture is adapted to forecasting several steps ahead and making almost optimal decisions.