Lying

[SoylentGreene]

When does not telling the truth become lying? Is lying always a sin or mortal sin?

[cappie]

Whether or not lying is WRONG is an objective question with a straightforward answer. Whether or not lying is a SIN is an entirely separate question because culpability in sin has qualifiers (knowledge, free will, matter). In other words, someone may do that which is WRONG, but because one of these factors is missing, they may not have incurred SIN.

It depends on the situation and your intention. If your intention is to save yourself trouble or grief over something you have done that you should not have done, or did not do that you should have done, then not telling is probably the same as lying -- your purpose is to deceive.

On the other hand, if you have nothing to gain and your purpose is to protect the other person from pain or grief then not telling, while technically no different from lying, may be the right thing to do and therefore acceptable.

When is lying considered mortal sin?

CCC #2484 The gravity of a lie is measured against the nature of the truth it deforms, the circumstances, the intentions of the one who lies, and the harm suffered by its victims. If a lie in itself only constitutes a venial sin, it becomes mortal when it does grave injury to the virtues of justice and charity.