No being is called evil by participation, but by privation of participation.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic evil participation
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

“but privation and evil by receding from that term. Hence a thing is not said to be evil and worse, by reason of access to the supreme evil, in the same way as it is said to be good and better, by reason of access to the supreme good. Reply Obj. 4: No being is called evil by participation, but by privation of participation. Hence it is not necessary to reduce it to any essential evil. Reply Obj. 5: Evil can only have an accidental cause, as was shown above (A. 1) . Hence reduction to any 'per se' cause of evil is impossible.” source