| Abstract: | Necessary and sufficient conditions for the existence of a probability measure agreeing with a weak order on an algebra of events are given. In the case of a countable algebra they consist of an extension of Kraft, Pratt, and Seidenberg's (1959. Annals of Mathematical Statistics, 38, 780–786) additivity condition through the requirement of an Archimedean property. In the case of a σ-algebra and a σ-additive agreeing probability, Villegas' (1964. Annals of Mathematical Statistics, 35, 1787–1796) monotone continuity condition, which becomes necessary, is merely added to them. |
