A Logical Approach to de Finetti’s Notion of Event

Tommaso Flaminio (University of Insubria)

De Finetti’s conception of events is one of the most distinctive aspects of his theory of probability, yet it appears to be somewhat elusive.Indeed, the crux of his argument is the identification of the agent’s degrees of belief with the price they are willing to pay for an uncertain reward which depends on the future truth value of some presently unknown propositions – the events on which the agents are betting. This clearly suggests that the semantics of events, which bears directly on the definition of probability, is implicitly endowed with an epistemic structure. The purpose of this paper is to give this structure an explicit formal characterisation and to show how the resulting framework helps us making de Finetti’s elusive notion of event much clearer.