Summa Theologica

By Thomas Aquinas

OF THE VICES OPPOSED TO TRUTH, AND FIRST OF LYING (FOUR ARTICLES)

We must now consider the vices opposed to truth, and (1) lying: (2) dissimulation or hypocrisy: (3) boasting and the opposite vice. Concerning lying there are four points of inquiry:

(1) Whether lying, as containing falsehood, is always opposed to truth?

(2) Of the species of lying;

(3) Whether lying is always a sin?

(4) Whether it is always a mortal sin?