Full Idea
Any kind of excellence renders that of which it is the excellence good, and makes it perform its function well; thus the excellence of the eye makes both the eye and its function good.
Gist of Idea
If a thing has excellence, this makes the thing good, and means it functions well
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1106a17)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.99
A Reaction
To say that a thing's excellence makes it good seems tautological to us, but Aristotle perceives a family of concepts (such as good, fine, excellent, and functioning well) which capture different psychological states. We need 'good', as well as 'right'.
Related Idea
Idea 2095 If something has a function then it has a state of being good [Plato]