On the logical structure of de Finetti's notion of event

This paper sheds new light on the subtle relation between probability and logic by (i) providing a logical development of Bruno de Finetti’s conception of events and (ii) suggesting that the subjective nature of de Finetti’s interpretation of probability emerges in a clearer form against such a logical background. By making explicit the epistemic structure which underlies what we call Choice-based probability we show that whilst all rational degrees of belief must be probabilities, the converse doesn’t hold: some probability values don’t represent decision- relevant quantifications of uncertainty.