The origins of de Finetti's critique of countable additivity

Bruno de Finetti was one of the most convinced advocates of finitely additive probabilities. The present work describes the intellectual pro- cess that led him to support that stance and provides a detailed account both of the first paper by de Finetti on the subject and of the ensuing correspondence with Maurice Fr\'echet. Moreover, the analysis is supplemented by a useful picture of de Finetti's interactions with the international scientific community at that time, when he elaborated his subjectivistic conception of probability.