One of the surest tests [of the superiority or inferiority of a poet] is the way in which a poet borrows. Immature poets imitate; mature poets steal; bad poets deface what they take, and good poets make it into something better, or at least something different. The good poet welds his theft into a whole of feeling which is unique, utterly different than that from which it is torn; the bad poet throws it into something which has no cohesion. A good poet will usually borrow from authors remote in time, or alien in language, or diverse in interest.

Eliot, T.S., “Philip Massinger,” The Sacred Wood, New York: Bartleby.com, 2000.

The source of this quote is Nancy Prager’s research as shown in this 2007 article, so kudos to her.

I found it thanks to this 2011 post by David Barnard that was quoted by John Gruber here. Thanks to all of them.

And as a bonus, I found this source for authoritative quotations, that’s going straight to my bookmarks.