Full Idea
We must regard music as a stimulus to virtue, capable of making a certain kind of character (just as gymnastic training produces a body of a certain type).
Gist of Idea
Music can mould the character to be virtuous (just as gymnastics trains the body)
Source
Aristotle (Politics [c.332 BCE], 1339a20)
Book Reference
Aristotle: 'Politics', ed/tr. Sinclair,T.A. /Saunders,T. [Penguin 1992], p.462
A Reaction
He makes a sustained claim for this, but without explicit justification. I am totally convinced that the music of Bach improves us, but I have no idea why.