 The key theoretical innovation is to appeal to the notion of functional explanation, also sometimes called “consequence explanation” (Cohen 1978 [2001]: 249–296). The essential move is cheerfully to admit that the economic structure, such as capitalism, does indeed develop the productive forces, but to add that this, according to the theory, is precisely why we have capitalism (when we do). That is, if capitalism failed to develop the productive forces it would disappear. And, indeed, this fits beautifully with historical materialism. For Marx asserts that when an economic structure fails to develop the productive forces—when it “fetters” the productive forces—it will be revolutionised and the epoch will change. So the idea of “fettering” becomes the counterpart to the theory of functional explanation. Essentially fettering is what happens when the economic structure becomes dysfunctional.