How To Assign Probabilities If You Must

Empirical evidence can sometimes be incorporated in a probabilistic analysis by conditioning with respect to the observations. Usually, the underlying probability distribution and also the conditional distribution are not completely known. The assignment of probabilities will then require a compromise. The making of such a compromise goes beyond mathematical theory: a statistical discussion is needed. It depends on the context whether the result of such discussion is almost compelling, reasonable, or not really agreeable. This is illustrated by means of a simple example from the area of predictive distributional inference.