Given the growing interest of economists in the philosophy of science and the lack of consensus among economic schools, the epistemology deployed by Keynes in his economic writings is evidently relevant and topical. As early as 1937 Leontief thought that any ‘show-down between the Cambridge … and the orthodox type of theory … must be fought out on methodological grounds’ (1937 p. 337; 1966 p. 58), a view generalised by Blaug’s dictum (1980 p. xiii) that ‘every controversy in economics involves questions of economic methodology’. But compared to the stature accorded Keynes in theory and policy, it is remarkable how insignificant a role he is given in discussions of the philosophy and methodology of economics. The giant of one sphere is a virtual non-entity in the other. While the methodological views of his father (whose impact on theory and policy was negligible) have received considerable attention, those of the son have drawn only isolated comment despite his extensive philosophical background. The lacuna, fortunately, is remediable.2