Concerning the Ten Commandments, which are the Heads of the Law (86-88)

For an oath is the calling of God to give his testimony concerning the matters which are in doubt; and it is a most impious thing to invoke God to be witness to a lie.

Come now, if you please, and with your reason look into the mind of the man who is about to swear to a falsehood; and you will see that it is not tranquil, but full of disorder and confusion, accusing itself, and enduring all kinds of insolence and evil speaking;

for the conscience which dwells in, and never leaves the soul of each individual, not being accustomed to admit into itself any wicked thing, preserves its own nature always such as to hate evil, and to love virtue, being itself at the same time an accuser and a judge; being roused as an accuser it blames, impeaches, and is hostile; and again as a judge it teaches, admonishes, and recommends the accused to change his ways, and if he be able to persuade him, he is with joy reconciled to him, but if he be not able to do so, then he wages an endless and implacable war against him, never quitting him neither by day, nor by night, but pricking him, and inflicting incurable wounds on him, until he destroys his miserable and accursed life.

"What sayest thou?" I should say to the perjured man, "will you dare to go to any one of your own acquaintances and say, My friend, come and bear witness for me that you have seen and heard, and been present at a whole catalogue of things which you have neither seen, nor heard? I think not; for that would be an act of incurable insanity;