Patrick O'Brien and Leandro Prados de la Escosura say they are discussing «the economic consequences of empire», but in fact they are discussing «the costs and benefits of European imperialism». This is clearer and more specific, but I fear less useful. It is clearer, since «costs and benefits» are easier to quantify, and less useful in that I do not agree that «economic consequences» are the same as, or can be reduced to, an assessment of «costs and benefits». Furthermore, as they themselves note, «counterfactual assumptions are… implicit in any attempt… to measure costs and benefits of macro economic strategies» (O'Brien & Prados, 1998, p. 31), and I shall want to argue that what we need to do is make «factual assumptions».