Question about full knowledge of mortal sin

1859 Mortal sin requires full knowledge and complete consent. It presupposes knowledge of the sinful character of the act, of its opposition to God’s law.

For example, if i steal something, knowing it is wrong, and still doing it, but not really with the intention or knowing that i’m sinning, offending God or going against the Church doctrine, it’s still mortal sin?

1860 Unintentional ignorance can diminish or even remove the imputability of a grave offense. But no one is deemed to be ignorant of the principles of the moral law, which are written in the conscience of every man.

I’m kinda confused. My question is if someone does something knowing it’s morally wrong, but not really knowing it is a mortal sin or with the intention to go against God’s will, it is not a mortal sin?

Didn’t really understood these parts of the catechism, full knowledge, moral law in the conscience of every man, so if someone could help… And sorry about my english

Everyone knows that stealing is wrong. Whether it is a mortal or venial sin depends on various factors. Stealing a handful of peanuts is obviously not a mortal sin.

Stealing a handful of peanuts could be a mortal sin if it is done with great malice, or - for example - if that particular handful of peanuts is snatched from the hand of a malnourished human being in great poverty. Or likewise, stealing a Ferrari could be a venial sin. If the conditions & intentions are appropriately there, stealing a peanut is all that is necessary to condemn a soul to everlasting damnation, whereas on the contrary, persecuting & killing Christians might not be.

The Catechism provides Church teachings to the faithful as is necessary to live a holy life and gain salvation, but does not (and cannot) dissect every nuance of God, man, and morality. We do not have precise, mathematical formula for what is mortal or venial sin; we simply know that not all sins are equal (as revealed in St John’s epistles) and the Church Fathers have historically delineated this as venial and mortal. St Aquinas presents his best effort to dig deeper into this, but by his own admission, the judgement of each man is a mystery that is reserved in the hereafter.

If a person is ever disturbed, they should take that opportunity to thank God for his unfailing love, and then they should make an examination of conscience, an act of contrition, and then be moved to Confession along with spiritual direction, and of course, trusting with great hope in the mercy of God and in the intervention of the saints to act as his hand. We always pray at the end of the Hail Mary, “pray for us, now and at the hour of our death”.

If it wasn’t given to you it isn’t yours.
Everyone knows that is wrong whether God said so or not surely?

For a wrong to be mortal it must be “grave matter” for a start.
Trivial thefts are “light matter” so mortal sin is impossible.
The sin is venial if you are more than sleep-walking.

Significant thefts will be grave matter.

Next question?

A person can know that say stealing someones car is rather wrong - and could commit a mortal sin - even though they do not know that term.

But if say sam takes a car thinking it it his - well that is a mistake. One he realizes this he returns it. Not a sin.

Perhaps more discussion can uncover more questions?

The poster said “steal” not “take thinking it’s mine”.
He also said “knowing it is wrong” so your 2nd point is not applicable.

Was commenting on the rest of the post. Where he quotes 1860

The Church teaches what it teaches in an objective sense. The teaching is binding.

And, whether a person’s conscience and knowledge are fully formed is not something the Church can definitively pronounce. The person stands before God who alone can judge the person’s culpability.

Mortal sin is the death of a person’s relationship to God. The objective teaching of the Church exists to unify the faithful, not to exalt the personal conscience in opposition to the teaching.
It’s probably a good thing that no pat answer exists for every unique and real situation. This causes us to further search our conscience, to refine it, to repent, to conform ourselves to the teaching of the Church.

I am aware.

Is taking what you think is your own car a “grave offence”.

In short is the “grave” in this phrase referring to the accidental or substantial severity of the offence?

“1860 Unintentional ignorance can diminish or even remove the imputability of a grave offense.”

It is referring there to the possibility that such ignorance can lessen the guilt or even remove the guilt regarding the gravely sinful act in question (the act itself is a grave offense (perjury is a grave sin for example) - but is the person not fully guilty or maybe even not guilty at all of sin here and now due to such ignorance?).

You didn’t actually address either of my questions directly:

Is taking what you [mistakenly] think is your own car a “grave offence”.

Your 1860 comment is only applicable if this is true.

If the “gravity” of the “gravel offence” is about culpability…then it obviously isn’t a grave offence to take what you believe is your own car.

If the “gravity” refers to the object matter of the offence then 1860 is applicable because you have taken an item of significant value from another - this is grave matter in my mind.

So do you still hold 1860 is applicable to the poster’s specific example?
If so then you must logically conclude you believe the “grave” in “grave offence” referred to in 1860 is only about grave matter surely?

Or you believe the contributors example was one of “stealing” …which it clearly is not.

You haven’t directly tackled the issue with your 2nd point which was:

But if say Sam takes a car thinking it it his - well that is a mistake. … Not a sin.

I believe this is not strictly correct.
It is obviously not a moral fault or moral offence.
But sin encompasses a wider range of evils than just “moral faults” as Aquinas states.

Taking an object of value that belongs to another is a “grave matter” regardless of whether you bring it back later or not. It is still unjustly depriving another of the use of their property, it is still grave matter surely?

Therefore it is still a serious offence, (i.e. a serious sin) even if there is absolutely no culpability, no serious moral offence, no moral fault.

I was referring in that place to the committing of a sin. Culpability.

Sam made a mistake - not committed a sin. Or in short hand - well that was a mistake not a sin.

The bolded is not correct moral theology. Grave matter is not equal to sin necessarily.
And the word “offence” may not apply either, depending on what exactly you mean.
(no I don’t wish to go on parsing “offense”)


Actually there is a objective level (the thing itself)
and a subjective level (the culpability).

Adultery* is* a grave sin*

A particular person may not be* culpable* for grave sin* due to lack of knowledge or deliberate consent - but adultery remains a grave sin itself.

If one is using the term “grave matter” that yes can help clarify things but it is still the case that one can simply refer to say the grave sin* of adultery (irrespective of the culpability).

*(mortal sin, serious sin - the terms refer to the same sin)
I get all that. I was not responding to that, but to the formulation of the other poster.

You are mistaken.
It is legitimate to call this mistake, this offence, a sin - though not a moral fault.

He materially transgressed the law.
He deprived another of the possession and use of a valuable piece of property.
That is an evil.
That is grave matter as specified by the 7th Commandment.
He therefore engaged in a transgression of grave matter.

This is legitimately called a sin of grave matter because moral fault (malum culpae) is not the only species of evil contained by the genus “sin”. Malum poenae (mere actions of grave or light matter) is another species of evil within the genus of “sin”.
Regardless of moral fault or not it is therefore still validly called “sin.”

*"… we call sins acts lacking due order or form or measure. … And we call limping itself a sin, since we can call any disordered act a sin, whether of nature or human skill or morals. … sin has the nature of moral wrong only when it is voluntary… And so sin is evidently more general than moral wrong, although the common usage of theologians takes sin and moral wrong to be the same." *(Aquinas)

It can also be called a “serious” sin in so far as the gravity of the matter (as opposed to the gravity of the culpability - as in mortal or venial) modifies the sin.

Sin can be described as “serious” from two different perspectives: by reason of the action itself (i.e. its matter) or by reason of the agent’s culpability"

“We can weigh the gravity of sin in two ways: in one way regarding the very act; in the second way regarding the one who sins.” (Aquinas)

I disagree, see Aquinas below.

“Offences” are “transgressions of Law”.
One can transgress the law without being culpable (ie no moral fault).
But it is still a disordered action by means of the matter.
Hence it is still an offence and for that reason also, still validly called a sin - especially if grave matter is involved.

And so sin is evidently more general than moral wrong, although the common
usage of theologians takes sin and moral wrong to be the same." (Aquinas)

I can only analyse what you wrote.
"if say Sam takes a car thinking it it his … that is a mistake. … Not a sin. "

It IS validly called a “sin”.
He engaged in a gravely disordered act even if not a “moral fault”.
That is still “sin” as Aquinas affirms.

“Sin” and “moral fault” are not univocal terms.
Sin is the set, “moral fault” is but a sub-set.
It also includes another sub-set, non-culpable disordered acts.

I believe you meant to write:
"if say Sam takes a car thinking it it his … that is a mistake. … Not a moral fault." OR
"if say Sam takes a car thinking it it his … that is a mistake. … Not a mortal sin."

Your missed some of my posts it seems.

I noted up above that there is sin in the objective sense.

Adultery* is *a grave sin.

It remains so even if the person is not culpable for it seriously.

And there is sin the in subjective sense.

“Sam is guilty of grave sin”

(I set aside the example of theft for that can be a bit more tricky - one would see the definition of what theft is and is not in the CCC-- and there is not point it getting all into it for that is not the OP’s question and thus is not the topic).

DISCLAIMER: The views and opinions expressed in these forums do not necessarily reflect those of Catholic Answers. For official apologetics resources please visit