Anger is said to grow into hatred, not as though the same passion which at first was anger, afterwards becomes hatred by becoming inveterate
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic anger passion
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

“Cicero gives the name of desire to any kind of craving for a future good, without discriminating between that which is arduous and that which is not. Accordingly he reckons anger as a kind of desire, inasmuch as it is a desire of vengeance. In this sense, however, desire is common to the irascible and concupiscible faculties. Reply Obj. 2: Anger is said to grow into hatred, not as though the same passion which at first was anger, afterwards becomes hatred by becoming inveterate; but by a process of causality. For anger when it lasts a long time engenders hatred. Reply Obj. 3: Anger is said to be composed of sorrow and desire, not as though they were its parts, but because they are its causes:” source