This paper endorses Marx's deduction of the need for money to actualise value before exchange can be considered, so that, in exchange, money's function as means of purchase follows from money's ability to actualise value. This is contrasted with the Uno school, whose proponents mix concepts from Capital chapters 1 and 2. The paper goes beyond Marx in presenting a more dialectical derivation of money and a more rigorous account of the logic of exchange. The view of money advanced here gives a basis for its active role in the development of capitalism.