Hence it is more in opposition to truth, considered as a moral virtue, to tell the truth with the intention of telling a falsehood than to tell a falsehood with the intention of telling the truth.
 Thomas Aquinas, Summa Theologica (1274). copy citation

add
Author Thomas Aquinas
Source Summa Theologica
Topic falsehood opposition
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

“Therefore it is evident that lying is directly an formally opposed to the virtue of truth.
Reply Obj. 1: We judge of a thing according to what is in it formally and essentially rather than according to what is in it materially and accidentally. Hence it is more in opposition to truth, considered as a moral virtue, to tell the truth with the intention of telling a falsehood than to tell a falsehood with the intention of telling the truth. Reply Obj. 2: As Augustine says (De Doctr. Christ. ii) , words hold the chief place among other signs. And so when it is said that "a lie is a false signification by words," the term "words" denotes every kind of sign.” source