Full Idea
The conviction which impels us towards excellence is rational, and the power by which it masters us we call self-control.
Clarification
'Excellence' here is the Greek word 'areté', which also translates as 'virtue'
Gist of Idea
Reason impels us towards excellence, which teaches us self-control
Source
Plato (Phaedrus [c.368 BCE], 237e)
Book Reference
Plato: 'Phaedrus and Letters VII and VIII', ed/tr. Hamilton,Walter [Penguin 1973], p.37