But one can be ungrateful by committing different kinds of sin, for instance by calumny, theft, or something similar committed against a benefactor. Therefore ingratitude is not a special sin.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic theft ingratitude
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/18755/pg18755-images.html

Context

“For whoever sins acts against God his sovereign benefactor. But this pertains to ingratitude. Therefore ingratitude is not a special sin.
Obj. 2: Further, no special sin is contained under different kinds of sin. But one can be ungrateful by committing different kinds of sin, for instance by calumny, theft, or something similar committed against a benefactor. Therefore ingratitude is not a special sin. Obj. 3: Further, Seneca writes (De Benef. iii) : "It is ungrateful to take no notice of a kindness, it is ungrateful not to repay one, but it is the height of ingratitude to forget it." Now these do not seem to belong to the same species of sin.” source