A double-minded man is inconstant in all his ways.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic
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

“It would seem that the aforesaid vices do not arise from lust. For inconstancy arises from envy, as stated above (A. 5, ad 2) . But envy is a distinct vice from lust. Obj. 2: Further, it is written (James 1:8) : "A double-minded man is inconstant in all his ways." Now duplicity does not seem to pertain to lust, but rather to deceitfulness, which is a daughter of covetousness, according to Gregory (Moral. xxxi, 45) . Therefore the aforesaid vices do not arise from lust.” source