For since it is fraught with greater danger and is more annoying to others, it is more repugnant to prudence to think or boast that one has what one has not, than to think or say that one has not what one has.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic danger prudence
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

“In this way it does not belong to this virtue to incline to what is less, because this would imply falsehood. And yet this would be less repugnant to the truth, not indeed as regards the proper aspect of truth, but as regards the aspect of prudence, which should be safeguarded in all the virtues. For since it is fraught with greater danger and is more annoying to others, it is more repugnant to prudence to think or boast that one has what one has not, than to think or say that one has not what one has. This suffices for the Replies to the Objections. _______________________
QUESTION 110 OF THE VICES OPPOSED TO TRUTH, AND FIRST OF LYING (In Four Articles)
We must now consider the vices opposed to truth, and (1) lying: (2) dissimulation or hypocrisy: (3) boasting and the opposite vice.” source