Active power is not contrary to act, but is founded upon it, for everything acts according as it is actual: but passive power is contrary to act; for a thing is passive according as it is potential.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic potential power
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

“whereas passive power is the principle of being acted upon by something else, as the Philosopher says (Metaph. v, 17) . It remains, therefore, that in God there is active power in the highest degree. Reply Obj. 1: Active power is not contrary to act, but is founded upon it, for everything acts according as it is actual: but passive power is contrary to act; for a thing is passive according as it is potential. Whence this potentiality is not in God, but only active power. Reply Obj. 2: Whenever act is distinct from power, act must be nobler than power. But God's action is not distinct from His power, for both are His divine essence;” source