 Philosophers as well as the practitioners of any discipline have to conceptualize what is essential, although he points out that the accidental and the essential often coincide in one subject. The Alfarabian fourth section describes the five ways of anterior and posterior: in time, by nature, in precedence, in excellence, as cause to effect and his division echoes that of Aristotle in the book of Categories. Avempace sees the distinction as the way to understand equivocity — primary and derivative sense, and focuses on three senses of anterior and posterior: in precedence, in excellence, as cause, because the three kinds concern conceptualization and assent.