From Formal Logic to Human Logic: An Inquiry into Keynes’s Philosophical Reasoning

This paper argues that the development of John Maynard Keynes’s thought, from A Treatise on Probability (TP, 1921) to The General Theory (GT, 1936), is best understood as a process of methodological evolution in which the formal logic of probability is progressively reformulated as a human logic of uncertainty. Drawing on the documented influences of G. E. Moore and Bertrand Russell on the young Keynes, and engaging with a pragmatist reading of Keynes, we argue that the notion of weight of argument functions as the methodological thread connecting the logical theory of probability of the TP to the state of confidence and to convention-based behaviour in Chapter 12 of the GT. The article situates this continuity in relation to Ramsey’s critique and to Keynes’s 1931 acknowledgement of the distinction between formal logic and human logic, interpreting it as a reconfiguration, rather than an abandonment, of the TP’s epistemological framework. This paper positions itself between discontinuity-based and rigid-continuity readings and contributes to the contemporary debate in economic methodology by emphasizing the deep continuity between Keynes’s philosophical realism and his treatment of decision-making under uncertainty.