Power is the principle whereby one thing acts on another.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic power principles
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

“for the act of sensation is perfected by the action of the sensible object upon sense. It follows that no other procession is possible in God but the procession of the Word, and of Love. Reply Obj. 1: Power is the principle whereby one thing acts on another. Hence it is that external action points to power. Thus the divine power does not imply the procession of a divine person; but is indicated by the procession therefrom of creatures. Reply Obj. 2: As Boethius says” source