For every defect is a kind of evil. But in all creatures there is the defect of not being able to preserve their own existence, which nevertheless is neither a pain nor a fault. Therefore evil is inadequately divided into pain and fault.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic pain evil
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17611/pg17611-images.html

Context

“[*Pain here means "penalty": such was its original signification, being derived from "poena." In this sense we say "Pain of death, Pain of loss, Pain of sense."—Ed.]
Objection 1: It would seem that evil is not adequately divided into pain and fault. For every defect is a kind of evil. But in all creatures there is the defect of not being able to preserve their own existence, which nevertheless is neither a pain nor a fault. Therefore evil is inadequately divided into pain and fault. Obj. 2: Further, in irrational creatures there is neither fault nor pain; but, nevertheless, they have corruption and defect, which are evils. Therefore not every evil is a pain or a fault.
Obj. 3: Further, temptation is an evil, but it is not a fault; for "temptation which involves no consent, is not a sin, but an occasion for the exercise of virtue," as is said in a gloss on 2 Cor.” source