A man may be virtuous without having full use of reason as to everything, provided he have it with regard to those things which have to be done virtuously.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic reason
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

“wherefore such an inclination does not of necessity require reason. But the inclination of moral virtue is with choice: and consequently in order that it may be perfect it requires that reason be perfected by intellectual virtue. Reply Obj. 2: A man may be virtuous without having full use of reason as to everything, provided he have it with regard to those things which have to be done virtuously. In this way all virtuous men have full use of reason. Hence those who seem to be simple, through lack of worldly cunning, may possibly be prudent, according to Matt. 10:16: "Be ye therefore prudent (Douay:” source