When we do a thing for a good and lawful purpose, if thereby we unintentionally cause harm to anyone, it should by no means be imputed to us.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic purpose harm
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

“contain several canons prescribing penalties for unintentional homicide. Now penalty is not due save for guilt. Therefore he who kills a man by chance, incurs the guilt of murder. On the contrary, Augustine says to Publicola (Ep. xlvii) : "When we do a thing for a good and lawful purpose, if thereby we unintentionally cause harm to anyone, it should by no means be imputed to us." Now it sometimes happens by chance that a person is killed as a result of something done for a good purpose. Therefore the person who did it is not accounted guilty. I answer that, According to the Philosopher” source