What if?’ books today occupy a prominent place in airport bookshops and have become a major publishing success. Yet this approach, generally known as counterfactualism, has had only a limited impact on academic history. Indeed counterfactualism has been strongly dismissed by prominent historians of the Left, including E. H. Carr, Richard Evans, Eric Hobsbawm, and E. P. Thompson. They have sought to portray counterfactualism as a plaything of the Right. What If? is a defence of counterfactualism and a guide to the subject by one of the UK s leading historians. Jeremy Black demonstrat¬es the place of contingency and human agency in history. The counterfactual approach to history, argues Professor Black, is so hated by some historians precisely because it presents a devastating critique to determinist – and especially Marxist – accounts of past, present and future.