An evil action can have a proper effect, according to the goodness and being that it has.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic goodness action
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

“and in a certain respect deficient in act, so as to cause a deficient act. Thus a blind man has in act the power of walking, whereby he is able to walk; but inasmuch as he is deprived of sight he suffers a defect in walking by stumbling when he walks. Reply Obj. 3: An evil action can have a proper effect, according to the goodness and being that it has. Thus adultery is the cause of human generation, inasmuch as it implies union of male and female, but not inasmuch as it lacks the order of reason. ________________________ SECOND ARTICLE [I-II, Q. 18, Art.” source