Counterfactual history, also sometimes referred to as virtual history, is a form of historiography that attempts to answer "" questions known as counterfactuals. Black and MacRaild provide this definition: "It is, at the very root, the idea of conjecturing on what did not happen, or what might have happened, in order to understand what did happen. The method seeks to explore history and historical incidents by means of extrapolating a timeline in which certain key historical events did not happen or had an outcome which was different from that which did in fact occur. It has produced a book genre which is variously called alternative history, speculative history, or hypothetical history.