It is by forming a right judgment of creatures that man becomes aware of the loss (of which they may be the occasion) , which judgment he exercises through the gift of knowledge.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic loss judgment
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

“. and a snare to the feet of the unwise," of those, namely, who do not judge aright about creatures, since they deem the perfect good to consist in them. Hence they sin by placing their last end in them, and lose the true good. It is by forming a right judgment of creatures that man becomes aware of the loss (of which they may be the occasion) , which judgment he exercises through the gift of knowledge. Hence the beatitude of sorrow is said to correspond to the gift of knowledge.
Reply Obj. 1: Created goods do not cause spiritual joy, except in so far as they are referred to the Divine good, which is the proper cause of spiritual joy.” source