Full Idea
We know of perfection as we look upon what is imperfect.
Gist of Idea
We know perfection when we see what is imperfect
Source
Iris Murdoch (Metaphysics as a Guide to Morals [1992], 13)
Book Reference
Epicurus: 'The Epicurus Reader', ed/tr. Inwood,B. /Gerson,L. [Hackett 1994], p.427
A Reaction
This is in the context of a discussion of the ontological argument for God's existence, but I seize on it as a nice expression of the idealisation capacity of our minds. The alternative is that perfection is innate idea, since we aren't seeing it.