Full Idea
The dialectical capacity - you won't give it to anyone else, I suspect, except to whoever philosophises purely and justly.
Clarification
'Dialectic' is the impersonal pursuit of truth
Gist of Idea
Dialectic should only be taught to those who already philosophise well
Source
Plato (The Sophist [c.358 BCE], 253e)
Book Reference
Plato: 'The Sophist', ed/tr. Bernadete,Seth [University of Chicago 1986], p.49