A story is a hypothetical historical narrative describing a process, or a narrative of particular events arranged in time and forming a meaningful totality. Historians tell stories to provide understanding of the past and use narratives as a form of explanation: "A narrative explanation, presumably, presents an account of the linkages among events as a process leading to the outcome one seeks to explain". William Whewell's term "colligation" has been borrowed by William Henry Walsh to describe "the procedure of explaining an event by tracing its intrinsic relations to other events and locating it in its historical context". "Historical" or "genetic" explanations are used also in evolutionary biology.