Moore’s early role in Cambridge philosophy and connections to Russell, Wittgenstein, and Keynes are described. His influence on Keynes’s early views is associated with Moore’s naturalistic fallacy idea and his open-question argument method of analysis. Moore and Keynes disagreed about how duty was to be explained owing to their differences over how the concept of probability was to be understood. Moore held a frequency view and Keynes believed probability was a matter of rational judgement. In his later “My early beliefs” memoir Keynes affirmed his attachment to Moore’s understanding of the good as what is intrinsically valuable and demurred from his view of duty and as conduct. Conventions were seen as central to the latter.

Russell’s influence on Cambridge philosophy is summarized in terms of his logicist attempt to derive all mathematical truths from the axioms and rules of inference of symbolic logic. Keynes’s Treatise on Probability is explained as a parallel attempt to explain the logical foundations of probability. His view was that probability was a matter of judgement and logic rather than statistical frequencies. The early Keynes also took up and extended Russell’s epistemological views, particularly the distinction between knowledge by acquaintance and knowledge by description. These views were later criticized by Ramsey. Different views regarding how Keynes addressed these criticisms of his early probability view are briefly summarized, and Russell and Keynes are compared in terms of their later careers.

Wittgenstein’s early and later philosophical views are distinguished. The change in his thinking occurred after his return to Cambridge in 1929, and concerned his turning away from formal logic to the nature of ordinary language. His later view associated meaning with language use, and in anthropological fashion he emphasized what people did with language in “language games”. The interaction between Keynes and Wittgenstein is briefly discussed. Keynes’s concept of convention emphasizes rules in much the way that Wittgenstein saw language-games as rule governed. Wittgenstein’s abandonment of the idea that language has meaning in virtue of its representing the world outside language is compared to Keynes’s beauty contest analogy regarding the determination of stock prices.

Ramsey’s brief career and connection to Wittgenstein and Keynes are described. Together with Keynes he was influential in getting Wittgenstein to return to Cambridge and complete the latter’s pre-World War I philosophy. Ramsey is credited with advancing an effective criticism of Keynes’s Treatise on Probability view that probability is an objective relationship, and offered an alternative, subjectivist understanding of probability which anticipated the future expected utility approach to choice behaviour in economics. Keynes’s response to Ramsey is discussed in terms of whether probability relations should be thought to exist or be seen as “useful mental habits”. Ramsey’s later influential papers on optimal saving and optimal taxation are briefly discussed.

In line with his commitment to Veblenian thinking and agency-structure reasoning, Geoff Hodgson rejects the subjectivist conception of individuals as collections of preferences and views individuals in objectivist terms as distinguishable sets of habits that co-evolve with cumulative change in social structures and institutions. The chapter draws on these ideas to propose an account of reflexive economic agents that explains choice behavior in a cumulative causation world, in which both linear causation and circular feedback effects matter. Reflexive agents know that their actions can influence their habits and alter the basis for future action, and therefore form expectations about the consequences of their actions not only on the external world but also on themselves. But reflexive agents are reference-dependent and biased toward the habits they already have, with the implication that they are not only distinguishable but also re-identifiable over time.