From the very fact that a man thinks evil of another without sufficient cause, he despises him unduly, and therefore does him an injury.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic evil injury
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

“Some kind of certainty is found in human acts, not indeed the certainty of a demonstration, but such as is befitting the matter in point, for instance when a thing is proved by suitable witnesses. Reply Obj. 2: From the very fact that a man thinks evil of another without sufficient cause, he despises him unduly, and therefore does him an injury. Reply Obj. 3: Since justice and injustice are about external operations, as stated above (Q. 58, AA. 8, 10, 11; Q. 59, A. 1, ad 3) , the judgment of suspicion pertains directly to injustice when it is betrayed by external action, and then it is a mortal sin, as stated above.” source