The facts of history have long been thought of as Contingent:Not determined by unchanging laws of nature or by divine will but instead produced by human beings, who are limited by circumstances yet capable of agency. The belief in the contingency of historical facts is an invitation to speculate about what might have happened instead, and the thought experiments we call counterfactual history accept that invitation by imagining alternative historical events. Before the scientific revolution, contingency was thought to be a characteristic of facts in general: the word fact was used mainly to describe the time-bound and particular deeds of humankind as opposed to the eternal and general truths of nature. The scientific revolution marked the beginning of a long process in which modern thinkers gradually developed the concept of the fact to mean any observable, freestanding, particular occurrence in history or nature. The idea that there were natural, as well as historical, facts became acceptable, whereas earlier it would have seemed self-contradictory (Shapiro).