For happiness is man's supreme perfection. Now each thing is perfect in so far as it is actual; since potentiality without act is imperfect.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic perfection happiness
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“(Ethic. i, 13) that "happiness is an operation according to perfect virtue." I answer that, In so far as man's happiness is something created, existing in him, we must needs say that it is an operation. For happiness is man's supreme perfection. Now each thing is perfect in so far as it is actual; since potentiality without act is imperfect. Consequently happiness must consist in man's last act. But it is evident that operation is the last act of the operator, wherefore the Philosopher calls it "second act" (De Anima ii, 1) : because that which has a form can be potentially operating, just as he who knows is potentially considering.” source