for a thing is perfect in proportion to its state of actuality, because we call that perfect which lacks nothing of the mode of its perfection.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic perfection state
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17611/pg17611-images.html

Context

“Now God is the first principle, not material, but in the order of efficient cause, which must be most perfect. For just as matter, as such, is merely potential, an agent, as such, is in the state of actuality. Hence, the first active principle must needs be most actual, and therefore most perfect; for a thing is perfect in proportion to its state of actuality, because we call that perfect which lacks nothing of the mode of its perfection. Reply Obj. 1: As Gregory says (Moral. v, 26,29) : "Though our lips can only stammer, we yet chant the high things of God." For that which is not made is improperly called perfect. Nevertheless because created things are then called perfect, when from potentiality they are brought into actuality, this word "perfect"” source