A common and successful strategy for explaining something scientifically is to describe the mechanism that produces it. Mechanisms are composed of entities and activities that are, in various senses, in the world. Entities are things that behave or engage in activities. Activities are ways of working that produce phenomena. Succinctly put, “mechanisms are entities and activities organized such that they are productive of regular changes from start or set-up to finish or termination conditions” (Machamer et al. 2000, p. 3). Mechanistic explanations are representations (often verbal descriptions) of mechanisms.