The Baltimore Catechism
378. Q. What is the Eighth Commandment?
A. The Eighth Commandment is: Thou shalt not bear false witness against thy neighbor.
Either in a court, while we are acting as witnesses, or by telling lies about him at any other time.
A. We are commanded by the Eighth Commandment to speak the truth in all things, and to be careful of the honor and reputation of everyone.
“Reputation.” If it be a sin to steal a man’s money, which we can restore to him, it is certainly a much greater sin to steal his good name, which we can never restore, and especially as we have nothing to gain from injuring his character. It is a sin to tell evil things about another–his sins, vices, etc.–even when they are true. The only thing that will excuse us from telling another’s fault is the necessity to do so in which we are placed, or the good we can do to the person himself or others by exposing faults. How shall you know when you have injured the character of another? You have injured another’s character if you made others think less of him than they did before. If you have exposed some crime that he really committed, your sin is called detraction; if you accuse him of one he did not commit, your sin is calumny; and if you maliciously circulate these reports to injure his character, your sin is slander. But how shall you make reparation for injuring the character of another? If you have told lies about him, you must acknowledge to those with whom you have talked that you have told what was untrue about him, and you must even compensate him for whatever loss he has suffered by your lies: for example, the loss of his situation by your accusing him of dishonesty. But if what you said of him was true, how are you to act? At every opportunity say whatever good you can of him in the presence of those before whom you have spoken the evil.
A. The Eighth Commandment forbids all rash judgments, backbiting, slanders, and lies.
“Rash judgment” — that is, having in your mind and really believing that a person is guilty of a certain sin when you have no reason for thinking so, and no evidence that he is guilty. “Backbiting” — that is, talking evil of persons behind their backs. You would not like your neighbor to backbite you, and you have no right to do to him what you would not wish him to do to you. Besides, everyone hates and fears a backbiter; because as he brings to you a bad story about another, he will in the same manner bring to someone else a bad story about you. It is certainly an honor to be able to say of a person: “He never has a bad word of anyone”; while on the other hand, he must be a despicable creature who never speaks of others except to censure or revile them. Never listen to a backbiter, detractor, or slanderer–it is sinful. Another way of injuring your neighbor is revealing the secrets he has confided to you. You will tell one friend perhaps and caution him not to repeat it to another; but if you cannot keep the secret yourself, how can you expect others to keep it? Again you may injure your neighbor by reading his letters without his consent when you have no authority to do so. This is considered a crime in the eyes even of the civil law, and anyone who opens and reads the letters of another can be punished by imprisonment. It is a kind of theft, for it is stealing secrets and information that you have no right to know. It is dishonorable to read another’s letter without his consent, even when you find it open. To carry to persons the evil things said about them by others so as to bring about disputes between them is very sinful. The Holy Scripture (Rom. 1:29) calls this class of sinners whisperers, and says that they will not enter into Heaven–that is, as long as they continue in the habit. If ever, then, you hear one person saying anything bad about another, never go and tell it to the person of whom it was said. If you do, you will be the cause of all the sin that follows from it–of the anger, hatred, revenge, and probably murder itself, as sometimes happens.
A. They who have lied about their neighbor and seriously injured his character must repair the injury done as far as they are able, otherwise they will not be forgiven.