A: The Eighth Commandment, Thou shalt not bear false witness, forbids false testimony in a court of justice, and it also forbids backbiting, detraction, calumny, adulation, rash judgment and rash suspicion and every sort of lying.
A: Detraction or backbiting is a sin which consists in making known another's sins and defects without sufficient reason.
A: Calumny is a sin which consists in maliciously attributing to another faults and defects which he did not possess.
A: Adulation is a sin which consists in deceiving another by falsely praising him or others for the purpose of profiting thereby.
A: Rash judgment or rash suspicion is a sin which consists in judging or suspecting evil of others without sufficient foundation.
A: A lie is a sin which consists in asserting as true or false by word or act that which one does not believe to be really the case.
A: There are three kinds: The jocose lie, the officious lie, and the malicious lie.
A: A jocose lie is that which is told in jest and without injury to anyone.
A: An officious lie is a false statement to benefit oneself or another without injuring anyone else.
A: A malicious lie is a false statement made to the injury of another.
A: It is never lawful to tell a lie, neither in joke, nor for one's own benefit, nor for the benefit of another, because a lie is always bad in itself.
A: A lie when jocose or officious is a venial sin; but when malicious it is a mortal sin if the harm done is grave.
A: It is not always necessary, especially when he who questions you has no right to know what he demands.
A: It is not enough for him who has sinned against the Eighth Commandment to confess the sin; he is also obliged to retract whatever he said when calumniating another, and to repair as far as he can the harm he has done.
A: The Eighth Commandment commands us to speak the truth at the proper time and place, and, as far as we can, to put a good interpretation upon the actions of our neighbor.