The demands of charity are most perfectly satisfied by men uniting together in the bonds that the various ties of friendship require, so that they may live together in a useful and becoming amity; nor should one man have many relationships in one, but each should have one.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic friendship relationship
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

“since through a man taking a stranger to wife, all his wife's relations are united to him by a special kind of friendship, as though they were of the same blood as himself. Wherefore Augustine says (De Civ. Dei xv, 16) : "The demands of charity are most perfectly satisfied by men uniting together in the bonds that the various ties of friendship require, so that they may live together in a useful and becoming amity; nor should one man have many relationships in one, but each should have one." Aristotle adds another reason (2 Polit. ii) : for since it is natural that a man should have a liking for a woman of his kindred, if to this be added the love that has its origin in venereal intercourse, his love would be too ardent and would become a very great incentive to lust:” source