Given from the Catholic Broadcasting Station 2SM Sydney Australia
Choose a topic from Vol 3:
In certain circumstances, they are. In others, they are not, and may even be obliged not to tell the truth. I might know some evil thing concerning you, yet I would be obliged by the very law of God not to tell it to others about you. Whilst, however, I am not always obliged to tell the truth, I am forbidden to tell lies.
On the grounds that a lie is essentially evil, and that we may not do evil that good may come. God Himself forbids lying. We are told that "lying lips are an abomination to the Lord." God is truth itself, and lying is falsehood. Therefore he that swerves from truth swerves from God. St. Thomas Aquinas says that God gave us speech to signify what is in the mind. He who speaks contrary to his mind violates the natural moral law itself.
No. The harm done to others is but the effect of a lie. It is not the lie itself. The lie itself is the deliberate expression of what one knows to be untrue, whether actual harm to others follows or not.