as man sins by choosing adultery, which is evil of itself.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic evil sin
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

“But for him to turn to God as the object of supernatural beatitude, comes of infused love, from which he could be turned away by sinning. Reply Obj. 4: Mortal sin occurs in two ways in the act of free-will. First, when something evil is chosen; as man sins by choosing adultery, which is evil of itself. Such sin always comes of ignorance or error; otherwise what is evil would never be chosen as good. The adulterer errs in the particular, choosing this delight of an inordinate act as something good to be performed now, from the inclination of passion or of habit;” source