“Ask a Priest: Can a Sin Be Mortal If a Person Doesn’t Know It Is Grave?”

Q: If you do not know something is a mortal sin, could it possibly have been a mortal sin? Also, if there is any doubt that something is a mortal sin, does that mean it wasn’t a mortal sin? I read these definitions from various Catholic websites online and wanted to check with a priest to make sure. – R.L.

Answered by Fr. Edward McIlmail, LC

A: The most direct answer to your question is: No, a person cannot commit a mortal sin without realizing that it is a mortal sin.

The Catechism makes this clear by pointing out that one of the three conditions necessary to commit a mortal sin is “full knowledge.”

No. 1857 says, “For a sin to be mortal, three conditions must together be met: ‘Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent.'”

The second part of your question opens up some other important issues — ones that can sometimes be difficult to clarify.

When there is real ignorance about an objectively grave sin, it might not be counted as a subjectively mortal sin. An example could be the case of contraception. It is objectively a gravely sinful act. Yet many spouses use it, never knowing that it undercuts the meaning of marital intimacy and can frustrate God’s plans for their marriage.

On the other hand, ignorance doesn’t take away all the effects of an objectively disordered act. In the case of a couple that uses contraception, even if they don’t understand the moral dimension of their act, they can still suffer the effects; for instance, a husband could start to become insensitive to his wife because he assumes she should be willing to be intimate whenever he wants.

Let’s turn to the case of a person who has doubts about whether something is a mortal sin. If the person doesn’t try to research the matter, and goes ahead and does the act, that very act could be a mortal sin, since he deliberately decided to risk a mortal sin, which could be a grave sin in itself. It shows a willingness to offend God gravely.

Similarly, some ignorance is culpable, or blameworthy, in itself. Ignorance can be the result of laziness or recklessness, for instance.

Take the case of a hunter who is out in the woods and sees a bush shaking. He opens fire, thinking there is a deer hiding behind it. If it turns out that he actually shoots another hunter, can he plead innocence based on ignorance? Hardly. He had the duty to be certain of what he was shooting at. His ignorance in this case was grossly, if not criminally, negligent.

So, if a person makes little or no effort to find out whether certain things are sinful, or if he ignores his conscience and doesn’t do any research, then his guilt would be culpable.

In cases where we later learn something we did was gravely sinful, we should mention that in confession. This helps us to put things behind us, leave them in God’s hands, and move on.

In any case, the ideal is that we learn our faith. We learn what the Church teaches about various topics. We are called to holiness, after all. We wouldn’t want ignorance to be an excuse for not going deeper into our faith.

Even amid ignorance there is often a little voice deep inside us that says something isn’t quite right. God alone knows the heart and mind of each person. God alone can judge when a person has sinned mortally.

For more reading, see the Catechism on the topic of moral conscience, starting at No. 1776, http://www.vatican.va/archive/ccc_css/archive/catechism/p3s1c1a6.htm. I hope some of this helps.

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