 Aristotle frequently compares the politician to a craftsman. The analogy is imprecise because politics, in the strict sense of legislative science, is a form of practical knowledge, while a craft like architecture or medicine is a form of productive knowledge. However, the comparison is valid to the extent that the politician produces, operates, maintains a legal system according to universal principles (EN VI.8 and X.9). In order to appreciate this analogy it is helpful to observe that Aristotle explains the production of an artifact such as a drinking cup in terms of four causes: the material, formal, efficient, and final causes (Phys. II.3 and Met. A.2). For example, clay (material cause) is molded into a roughly cylindrical shape closed at one end (formal cause) by a potter (efficient or moving cause) so that it can contain a beverage (final cause). (For discussion of the four causes see the entry on  Aristotle’s physics.)