  The notions of form and matter are themselves, however, developed within the context of a general theory of causation and explanation which appears in one guise or another in all of Aristotle’s mature works. According to this theory, when we wish to explain what there is to know, for example, about a bronze statue, a complete account necessarily alludes to at least the following four factors: the statue’s matter, its form or structure, the agent responsible for that matter manifesting its form or structure, and the purpose for which the matter was made to realize that form or structure. These four factors he terms the four causes (aitiai):