Full Idea
The ability to teach is a distinguishing mark between the knowledgeable and the ignorant man.
Gist of Idea
The ability to teach is a mark of true knowledge
Source
Aristotle (Metaphysics [c.324 BCE], 0981b04)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.5