As to universal principles of action, man is rightly disposed by the natural understanding of principles, whereby he understands that he should do no evil
 Thomas Aquinas, Summa Theologica (1274). copy citation

add
Author Thomas Aquinas
Source Summa Theologica
Topic action evil
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

“about which things actions are. Now right reason demands principles from which reason proceeds to argue. And when reason argues about particular cases, it needs not only universal but also particular principles. As to universal principles of action, man is rightly disposed by the natural understanding of principles, whereby he understands that he should do no evil; or again by some practical science. But this is not enough in order that man may reason aright about particular cases. For it happens sometimes that the aforesaid universal principle, known by means of understanding or science, is destroyed in a particular case by a passion:” source