For no power is a passion. But every love is a power, as Dionysius says (Div. Nom. iv) . Therefore love is not a passion.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic passion love
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

“Nom. iv) , "Beauty and goodness are beloved by all things"; since each single thing has a connaturalness with that which is naturally suitable to it. ________________________
SECOND ARTICLE [I-II, Q. 26, Art. 2]
Whether Love Is a Passion?
Objection 1: It would seem that love is not a passion. For no power is a passion. But every love is a power, as Dionysius says (Div. Nom. iv) . Therefore love is not a passion. Obj. 2: Further, love is a kind of union or bond, as Augustine says (De Trin. viii, 10) . But a union or bond is not a passion, but rather a relation. Therefore love is not a passion.
Obj. 3: Further, Damascene says (De Fide Orth. ii, 22) that passion is a movement.” source