“Ask a Priest: Do Previously Forgotten Mortal Sins Need to Be Confessed?”

Q: I am confused about mortal sin when it comes to forgetting one in confession. One Catholic apologist states that if one forgets a mortal sin in confession, as long as they intended to confess all of their mortal sins in kind and number and took the time to make a diligent examination of conscience, then the confession was valid and all sins are forgiven. And I agree with this part. But I don’t understand why one would have to later confess the forgotten sin if it has already been forgiven. Would it be a sin not to confess the forgotten mortal sin? I found another website that seems to agree with what I said. Also I have heard that if one deliberately conceals a mortal sin in confession, then the whole confession is invalid and even if other mortal sins were mentioned then they have to be confessed again. Some say, though, that it is just incomplete and what one has brought forward is forgiven, but the other mortal sin still remains and one has to confess just that sin and the sin of not saying it the first time. –S.P.

Answered by Fr. Edward McIlmail, LC

A: The Council of Trent said that confession must be complete in number and species with respect to mortal sin, although without having to go into lurid details.

There is a great difference between inadvertently forgetting a sin and deliberately concealing it. In the first case the sin is forgiven by the sacramental grace, in the second the sacrament is invalid and one has also committed a mortal sin of sacrilege. Which means none of the sins confessed are forgiven. So all mortal sins would have to be confessed the next time.

If one remembers a mortal sin that was left out by accident, then, yes, one should confess it at the next opportunity. This is so as to complete the former confession. Thus, to deliberately withhold mention of a previously forgotten mortal sin would seem to be grave matter.

Remembering the sin does not place one in mortal sin again, and it is not necessary to rush to confession. It is enough to mention it at the next regular confession; and one may continue to receive Communion in the meantime.

Plenty of online guides offer advice on making an examen of conscience, such as this guide.

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