Full Idea
Socrates was the first significant thinker to try basing ethics upon reason, and to try uncovering its natural principles solely by the use of reason.
Gist of Idea
Socrates was the first to base ethics upon reason, and use reason to explain it
Source
comment on Socrates (reports of career [c.420 BCE]) by Richard Taylor - Virtue Ethics: an Introduction Ch.7
Book Reference
Taylor,Richard: 'Virtue Ethics: an Introduction' [Prometheus 2002], p.45
A Reaction
Interesting. It seems to me that Socrates overemphasised reason, presumably because it was a novelty. Hence his view that akrasia is impossible, and that virtue is simply knowledge. Maybe action is not just rational, but moral action is.