Full Idea
If, in the case of things that are, the primary object is substance, then we can state the fundamental duty of the philosopher: it is to gain possession of the principles and causes of substances.
Gist of Idea
If substance is the basis of reality, then philosophy aims to understand substance
Source
Aristotle (Metaphysics [c.324 BCE], 1003b19)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.81