Withholding deliberate venial sins in confession?

If we have deliberately committed a venial sin, and we don’t mention it in confession, does that affect the validity of the sacrament?

What if the venial sin is directly connected to mortal sin?
For example, someone tells a lie in order to commit a serious sin. The deliberate lie itself might be venial (“I’m going straight home after work” when actually he/she drives to a lover’s house); but the reason is grave (to commit adultery).
If the deliberate lie is not confessed, but the adultery is, does that affect the validity of the confession?

Another consequent question: Does a venial sin become grave matter if it is committed with the intention of committing a mortal sin?

(Note: this is a hypothetical question, and not a personal confession)

Venial sin is not necessary matter for confession.

Now – for example --the lie was to ones wife-- hum–would such be “venial”?.


The confessor can guide them.

It may depend on what is meant.

I steal someone’s pencil that they need to use to pass their test that they need to pass in order to get a job.

Stealing a pencil usually can be called a venial sin. But in this case…well one is seeking to cause intentionally the person not to get the job. So such could be said to be grave.

Catechism:

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.

scborromeo.org

One who examined ones conscience and was intending to make a complete confession of their mortal sins and was contrite etc but* forgot a mortal sin* or say honestly judged it to be *venial *and thus deliberately omitted it. Such does not “invalidate” the confession. One needs to confess it in the next confession as it was --if one realized it was mortal.

Honestly, if it were me and I was that bothered by it, I would consider it the prompting of the Holy Spirit and just confess it next time.

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