By reason of itself, good is the object of pursuit, and evil, the object of avoidance: but by reason of something else, evil can be the object of pursuit, through some good attaching to it; and good can be the object of avoidance, through some evil attaching to it.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic evil reason
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“Now every movement of the appetitive power is reducible to one either of pursuit or of avoidance. Again, pursuit or avoidance is of something either by reason of itself or by reason of something else. By reason of itself, good is the object of pursuit, and evil, the object of avoidance: but by reason of something else, evil can be the object of pursuit, through some good attaching to it; and good can be the object of avoidance, through some evil attaching to it. Now that which is by reason of something else, follows that which is by reason of itself. Consequently pursuit of evil follows pursuit of good; and avoidance of good follows avoidance of evil. Now these four things belong to four passions, since pursuit of good belongs to hope, avoidance of evil to fear, the pursuit of the fearful evil belongs to daring, and the avoidance of good to despair.” source