Apart from being an extremely popular genre of science fiction literature, professional historians too describe and discuss alternative histories. In such an uchronia, one conjectures what would have happened if one or more past events happened otherwise. Although many historians either undervalue or neglect the role counterfactual reasoning plays in generating and warranting historical explanations, I argue in this paper that it is indispensable. My aim is to take away doubts about the usefulness of alternative histories, by showing that and how such speculations can be controlled.