 Functional explanation, so understood, renders these two claims—namely, that the relations of production are explained by the forces of production, and that the relations of production control the development of the forces of production—consistent. For instance, where relations of production endure (that is, exist in a stable fashion), they do so because they promote the development of the productive forces. And, where relations of production are revolutionised (that is, where old relations are abandoned for new ones), old relations cease to exist because they no longer favour the forces, and the new relations come into being (and/or come to preponderate) because they do favour the forces. On this reading, the impact of the relations on the forces is no embarrassment to Marx’s theory of history because of the functional manner in which it explains economic structures in terms of productive forces. Economic structures rise and fall according to whether they sustain or frustrate the development of the productive forces. To be clear, the suggestion is not, strictly speaking, that Marx propounds functional explanations, but rather that the claims which he does propound put severe constraints on the kind of explanation that is required, and that functional explanation is the most plausible candidate meeting those constraints.