Full Idea
Socrates is contradicting himself by saying virtue is not teachable, and yet trying to demonstrate that every virtue is knowledge.
Clarification
'Virtue' here is the Greek word 'areté', which also translates as 'excellence'
Gist of Idea
Socrates is contradicting himself in claiming virtue can't be taught, but that it is knowledge
Source
Plato (Protagoras [c.391 BCE], 361b)
Book Reference
Plato: 'Protagoras and Meno', ed/tr. Guthrie,W K C [Penguin 1956], p.99