Full Idea
Aristotle thinks that the explanation of how a thing is generated does not contribute to the explanation of why the thing is the very thing it is.
Gist of Idea
How a thing is generated does not explain its essence
Source
report of Aristotle (Metaphysics [c.324 BCE], ess) by Vassilis Politis - Aristotle and the Metaphysics 7.5
Book Reference
Politis,Vasilis: 'Aristotle and the Metaphysics' [Routledge 2004], p.241
A Reaction
Good for him. The origin of a thing strikes me as an entirely different matter from the intrinsic nature of the thing, and I don't see how the origin of something can be necessary, if it is in any way possible that it originated differently.