Now health is incompatible with disease. Therefore neither is passion compatible with virtue.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic health 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

“2: Further, virtue is a right affection of the soul, as health is to the body, as stated Phys. vii, text. 17: wherefore "virtue is a kind of health of the soul," as Cicero says (Quaest. Tusc. iv) . But the soul's passions are "the soul's diseases," as he says in the same book. Now health is incompatible with disease. Therefore neither is passion compatible with virtue. Obj. 3: Further, moral virtue requires perfect use of reason even in particular matters. But the passions are an obstacle to this: for the Philosopher says (Ethic. vi, 5) that "pleasures destroy the judgment of prudence": and Sallust says (Catilin.) that "when they," i.e. the soul's passions, "interfere, it is not easy for the mind to grasp the truth." Therefore passion is incompatible with moral virtue.
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