But sin is in the good of nature as an accident in a subject. Therefore sin does not diminish the good of nature, since to diminish is to act.
 Thomas Aquinas, Summa Theologica (1274). copy citation

add
Author Thomas Aquinas
Source Summa Theologica
Topic sin accident
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

“Obj. 4: Further, no accident acts on its subject: because that which is patient is a potential being, while that which is subjected to an accident, is already an actual being as regards that accident. But sin is in the good of nature as an accident in a subject. Therefore sin does not diminish the good of nature, since to diminish is to act. On the contrary, "A certain man going down from Jerusalem to Jericho (Luke 10:30) , i.e. to the corruption of sin, was stripped of his gifts, and wounded in his nature," as Bede [*The quotation is from the Glossa Ordinaria of Strabo] expounds the passage.” source