man, who is one natural being, though he has many parts, is composed of soul and body) ; so, in human acts, the act of a lower power is in the position of matter in regard to the act of a higher power, in so far as the lower power acts in virtue of the higher power moving it
 Thomas Aquinas, Summa Theologica (1274). copy citation

add
Author Thomas Aquinas
Source Summa Theologica
Topic virtue power
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

“In like manner also many individuals that are one in genus or species are many simply, and one in a certain respect: since to be one in genus or species is to be one according to the consideration of the reason. Now just as in the genus of natural things, a whole is composed of matter and form (e.g. man, who is one natural being, though he has many parts, is composed of soul and body) ; so, in human acts, the act of a lower power is in the position of matter in regard to the act of a higher power, in so far as the lower power acts in virtue of the higher power moving it: for thus also the act of the first mover is as the form in regard to the act of its instrument. Hence it is evident that command and the commanded act are one human act, just as a whole is one, yet in its parts, many.” source