Full Idea
Each man has knowledge when we think that he knows the primary cause or explanation ('proté aitia').
Gist of Idea
To know a thing is to know its primary cause or explanation
Source
Aristotle (Metaphysics [c.324 BCE], 0983a25)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.12
A Reaction
This seems to me to be the best starting point for individuation. Finding the 'origin' is not quite the same as finding the cause, and finding the 'role' or 'function' is parasitic on the underlying explanation or cause.