Between Keynes’s verbalized theory and its formal basis persists a lacuna. The conceptual groundwork is too small and not general. The quest for a comprehensive formal basis is guided by the question: what is the minimum set of foundational propositions for a consistent reconstruction of the money economy? We start with three structural axioms. The claim of generality entails that it should be possible to prove that Keynes’s formalism is a subset of the structural axiom set. The axioms are applied to a central part of the General Theory in order to achieve consistency and generality.