Does a mortal sin require knowing that the action is grave?


Does a mortal sin require knowing that the action is grave? If an action is wrong, and the action is grave, and a person knows that the action is wrong, but the person doesn’t know that the action is grave, and the person does the action, can it be a mortal sin?

The Catechism of the Catholic Church says that “Mortal sin requires full knowledge and complete consent.”( But this is unclear. Does the “full knowledge” refers to full knowledge of that the action is wrong, or full knowledge of that the action is wrong and the action is grave?

The Wikipedia says that “In Roman Catholic moral theology, a sin considered to be more severe or mortal is distinct from a venial sin and must meet all of the following conditions”, and one of the conditions is “It must be committed with full knowledge, both of the sin and of the gravity of the offense”( But, I am not sure whether this opinion is actually true in Catholicism.

So, does a mortal sin require knowing that the action is grave?

Please don’t just give a “yes” or “no” answer. Please also give the reason (for example, according to some authoritative document from the Catholic Church). Thanks!


The answer is yes. It’s in the CCC - full knowledge.

n. 1859 of the CCC:
“It presupposes knowledge of the sinful character of the act, of its opposition to God’s law.”

The sinful character of the act. Not simply just the sinful nature of the act, but it’s character, which to me, implies it’s nature and gravity.


Baltimore Catechism No 4 give more instruction on that issue:

*56 Q. How many things are necessary to make a sin mortal?
A. To make a sin mortal three things are necessary: a grievous matter, sufficient reflection, and full consent of the will.

“Grievous matter.” To steal is a sin. Now, if you steal only a pin the act of stealing in that case could not be a mortal sin, because the “matter,” namely, the stealing of an ordinary pin, is not grievous. But suppose it was a diamond pin of great value, then it would surely be “grievous matter.”

“Sufficient reflection,” that is, you must know what you are doing at the time you do it. For example, suppose while you stole the diamond pin you thought you were stealing a pin with a small piece of glass, of little value, you would not have sufficient reflection and would not commit a mortal sin till you found out that what you had stolen was a valuable diamond; if you continued to keep it after learning your mistake, you would surely commit a mortal sin.

“Full consent.” Suppose you were shooting at a target and accidentally killed a man: you would not have the sin of murder, because you did not will or wish to kill a man.

Therefore three things are necessary that your act may be a mortal sin:
INDENT The act you do must be bad, and sufficiently important;
(2) You must reflect that you are doing it, and know that it is wrong;
(3) You must do it freely, deliberately, and willfully.[/INDENT]


But this seems unclear on my question. It seems that “knowledge of the sinful character of the act” doesn’t necessarily include knowledge of that the act is grave.

Is there a very clear teaching on that?


This is clear. But, what is the authoritativeness of “Baltimore Catechism No 4”? Is it a catechism approved by a pope?


**Compendium issued by Pope Benedict XVI
394. How are sins distinguished according to their gravity?


A distinction is made between mortal and venial sin.
395. When does one commit a mortal sin?**


One commits a mortal sin when there are simultaneously present: grave matter, full knowledge, and deliberate consent. This sin destroys charity in us, deprives us of sanctifying grace, and, if unrepented, leads us to the eternal death of hell. It can be forgiven in the ordinary way by means of the sacraments of Baptism and of Penance or Reconciliation.
396. When does one commit a venial sin?**


One commits a venial sin, which is essentially different from a mortal sin, when the matter involved is less serious or, even if it is grave, when full knowledge or complete consent are absent. Venial sin does not break the covenant with God but it weakens charity and manifests a disordered affection for created goods. It impedes the progress of a soul in the exercise of the virtues and in the practice of moral good. It merits temporal punishment which purifies.



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. It also implies a consent sufficiently deliberate to be a personal choice. Feigned ignorance and hardness of heart133 do not diminish, but rather increase, the voluntary character of a sin.

Yes the knowledge needed yes includes that it is a grave matter. One need not say use that term - of course or need some particular theological knowledge - but yes one would know that it is serious. A man does not need to know the term “mortal sin” to know that murder is very serious - that it is opposed to the law of God.

There can be various sub -questions here that are best discussed with ones confessor -priest.


Now of course one is to “inform” and “form” ones conscience…that is part of the Christian life.


Jimmy Akin lists five catechisms used today:
*]St. Thomas Aquinas
*]Pius X
*]Catechism of the Catholic Church (second edition translation from Latin 1997 edition)
He notes that “The 1983 Code of Canon Law requires all new catechisms and new translations of catechisms to carry the imprimatur or be approved subsequently by ecclesiastical authority.” All five of them have that so therefore fulfill the canon law approved by the Holy See, so the Holy See (which includes the Pope) approves their use.

Baltimre Catechism has the official approbation of US bishops and used as the standard catechism for generations in the USA. The 1992 Catechism of the Catholic Church states that “this catechism is not intended to replace the local catechisms duly approved by ecclesiastical authorities, the diocesan bishops, and episcopal conferences, especially those that have received approval of the Holy See.”

*]Nihil Obstat: D. J. McMahon Censor Librorum
*]Imprimatur: + Michael Augustine Archbishop of New York New York, September 5, 1891
*]Nihil Obstat: Arthur J. Scanlan, S.T.D. Censor Librorum
*]Imprimatur: + Patrick J. Hayes, D.D. Archbishop of New York New York, June 29, 1921


Actually he has an extensive note regarding those earlier Catechisms.

and I would note that while one can learn much from them - of the ones you list it is the *Catechism of the Catholic Church *that is “used today” by the Church as is the Compendium and modern local Catechisms locally.

Of course the teaching regarding the three aspects needed to commit a mortal sin is basically the same in various Catechisms over time.


Ones confessor can guide one.

First one should not do something that is wrong of course.

Your sentence could apply to various different things…

For example

If one means that one had a general knowledge that such and such was wrong but honestly understood it to be light matter - and did it and then later discovered to ones shock that it is grave - that is one thing.

But it quite another for a person to say think - this is wrong and- I do not want to find out if it is serious - so I will do it and look later…or not look at all

Or he lets say it is something like he has good reason that such and such is grave but does not seek to find out …

*Rather *one should hold off and seek out what is the case before acting.

Ones confessor can guide one.

We are to inform and form our consciences according to the Teachings of the Church…

(now it can be a rather a different matter for a person with scruples …they would follow their regular confessors directions and principles he gives them to work against their scruples…to act against them…for they can see or fear sin where it is not due to their scruples…anyone in that boat see my post on scruples).


zhoudu;14363000]Does a mortal sin require knowing that the action is grave? If an action is wrong,** and the action is grave,** and a person knows that the action is wrong, but the person doesn’t know that the action is grave, and the person does the action, can it be a mortal sin?

You have been good and accurate answers with the best of references
Despite the confusing format of the original question.


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