In Karl Marx's Theory of History: A Defence (1978), G. A. Cohen has developed a distinctively functionalist interpretation of historical materialism. In this paper I outline Cohen's novel reconstruction of Marx and subject it to two independent internal criticisms. I first argue that explanations cannot conform to Cohen's functionalist model. I then suggest that even if there could be explanations having the structure he has proposed, they would fail to be helpful in illuminating the causal kernel of Marx's theory. Finally (...) I sketch a neglected but more promising approach to clarifying historical materialism, due to Geoffrey Hellman. (shrink)