On the axiomatisation of subjective probabilities

This paper essentially makes two remarks that are pertinent to many of the axiomatisations of subjective probability. First, the auxiliary experiment used to quantify qualitative feelings of relative likelihood is essentially distinct from the field of events of actual interest and may be kept so in the axiomatisation. Second, all theories of subjective probability agree that beliefs are conditional on the present state of knowledge and on the present mood and attitude of the individual concerned. As the individual moves through time this conditioning set, his knowledge and psychological state, change. This ever present change has implications for the conditions under which Bayes' Theorem may be invoked to prescribe how the individual should rationally update his beliefs in the light of a particular observation.