Therefore it is unlawful for any man to take another's life for the sake of the life of his own body.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic life body
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

“Arb. i, 5) : "How are they free from sin in sight of Divine providence, who are guilty of taking a man's life for the sake of these contemptible things?" Now among contemptible things he reckons "those which men may forfeit unwillingly," as appears from the context (De Lib. Arb. i, 5) : and the chief of these is the life of the body. Therefore it is unlawful for any man to take another's life for the sake of the life of his own body. Obj. 3: Further, Pope Nicolas [*Nicolas I, Dist. 1, can. De his clericis] says in the Decretals: "Concerning the clerics about whom you have consulted Us, those, namely, who have killed a pagan in self-defense, as to whether, after making amends by repenting, they may return to their former state, or rise to a higher degree; know that in no case is it lawful for them to kill any man under any circumstances whatever."” source