Aristotle's Doctrine of the Mean

Aristotle is considered the expert on virtue and the virtues. How did he develop Plato's ideas? Well, I think that term develop is exactly right because I think he does take over the Socratic Platonic agenda. The questions there are the questions that Plato was trying to answer. A virtue according to Aristotle is a disposition in Greek a hexis to perform certain actions and to feel certain feelings.