1. In the internal forum of conscience, no one is permitted to receive holy Communion if they realize they are unrepentant from actual mortal sin. It would be contrary to the eternal moral law to receive Communion in such a case, because the person is not in the state of grace. The Church has no authority to change the eternal moral law.
If the person repents from an actual mortal sin, committed since their last good confession, they usually must confess this actual mortal sin before reception of Communion. Some exceptions exist for a priest who must say Mass and has no other priest to hear his confession, or for lay persons who are in some grave circumstance (usually near death), as long as they first repent with perfect contrition.
“Can. 916 A person who is conscious of grave sin is not to celebrate Mass or receive the body of the Lord without previous sacramental confession unless there is a grave reason and there is no opportunity to confess; in this case the person is to remember the obligation to make an act of perfect contrition which includes the resolution of confessing as soon as possible.”
Does Canon 916 apply only to actual mortal sin, or does it apply to all objective mortal sin? My reading of this Canon (with consideration for the similar Canons in the 1917 Code — Can. 650, 699, cf. 1502, 1513) is that “mortal sin” specifically means actual mortal sin. For both Codes absolutely require an act of perfect contrition, without which Communion is forbidden even in danger of death. So the Canon implies that the mortal sin in question is actual mortal sin, which causes the loss of the state of grace. Perfect contrition is needed to return to the state of grace, absent confession.
What if the person realizes that they committed an objective mortal sin, one they judge not to be also an actual mortal sin due to a lack of full knowledge or full deliberation? The Church is free to decide the discipline in this case. Since the person reasonably believes himself to be still in the state of grace, the Church can permit reception, if She sees fit to do so. The minimum requirement for reception is the state of grace, and the past reception of the Sacrament of Baptism.
My preference for discipline in the case of objective mortal sin is to prohibit reception, with exceptions as stated above. The judgment that an objective mortal sin is not also an actual mortal sin is difficult and uncertain, especially when the person is a judge over his own case. Also, objective mortal sin, even when it is not also actual mortal sin, does grave harm to the person and to the Church and the world. So the Church has a compelling interest to correct persons who commit objective mortal sin by restricting them from reception of Communion, generally.
If Pope Francis decides otherwise, I would mildly faithfully reasonably disagree, without making any kind of accusation against him. I truly believe that Pope Francis will be canonized by the Church as a Saint. But he can still make some mistakes in discipline and personal opinion. Or perhaps the mistakes are on my part. God knows the truth.
2. In the external forum, persons who obstinately persevere in manifest grave sin are to be denied Communion.
“Can. 915 Those who have been excommunicated or interdicted after the imposition or declaration of the penalty and others obstinately persevering in manifest grave sin are not to be admitted to holy communion.”
The corresponding Canon in the old Code, which is not in force but does shed light, uses the term “external mortal sin” (old Code 440) in reference to denying Communion to a religious. This appears to have the same meaning as “manifest grave sin” in the new Code (915). The use of “grave sin” instead of “mortal sin” and the condition that the sin be “manifest” or “external” indicates objective mortal sin, regardless of whether there was full knowledge and full deliberation.
The phrase “obstinately persevering” indicates that this Canon does NOT apply to an occasional grave sin with repentance. Such cases would be subject to the internal forum, as discussed above (n. 1).
3. When is teaching heresy an actual mortal sin, and when it is merely an objective mortal sin (“grave sin”)?
Certainly, every actual mortal sin requires three conditions: grave matter, full knowledge, full deliberation. Adhering to heresy is objectively grave, but often this adherence is not also an actual mortal sin because the person does not realize that is belief is contrary to some infallible teaching of the Magisterium. If this heretical belief is not publicly known, Canon 915 does not apply. And if the error is not known to the person, in the internal forum of conscience, due to ignorance of Church teaching (or having been led astray by a false teacher), then it is not an actual mortal sin. The person may receive Communion in such a case. However, ignorance of Church teaching can be culpable, even to the extent of actual mortal sin, so a sincere examination of conscience is always advisable.
Teaching heresy is a graver sin than adhering to heresy. For many souls are harmed when heresy is taught or promoted publicly. And in the current circumstance today, heresy is often taught or promoted on the internet, thereby reaching souls around the world, causing much more harm. In such cases, the heresy often remains available online, so that the error continues to harm souls day after day, year after year.
The very grave sin of teaching heresy can be an actual mortal sin, in which case Communion is forbidden without repentance (and usually also confession). But many teachers of heresy do not appear to know that they are teaching a grave error. By a combination of ignorance and arrogance, they are blind to their own error. Sometimes this blindness is culpable, as it is willful or prideful.
Compared to mere adherence to heresy, the sin of teaching heresy is less easily reduced in culpability, because it is obvious to reason alone that every teacher of every subject must first study and understand what he wishes to teach. Very unfortunately, many teachers of Catholicism today teach without first having learned. They lack even a basic understanding of Church teaching on the very subject about which they presume to teach. So there is a greater likelihood that a Catholic who obstinately perseveres in teaching heresy is also guilty of actual mortal sin, at least by a grave negligence to first learn the faith before teaching it.
What if a person were to teach or practice medicine, without first studying the subject? Clearly, such a person sins gravely and may cause great harm to the health of those he teaches or treats. Yet many Catholics have no qualms or reservations in teaching on every subject in theology, with no substantial study of each subject area. They cause grave harm to many souls, without remorse.
Teaching heresy is objectively a grave sin, since souls are necessarily harmed by every gravely erroneous false doctrine, especially those contrary to the definitive teaching of the Roman Catholic Magisterium. And this sin is manifest (or external) because teaching, by definition, is an external and ordinarily also a public act. In the modern case of a person who teaches heresy on the internet, or in a widely published and available book, the sin is very manifest and does harm to many souls.
The condition of obstinate perseverance is met when the teacher of heresy is offered correction, privately or publicly, and he does not publicly correct his publicly taught heresy, nor remove its text from the internet (in so far as he is able).
4. Should teachers of heresy be denied Communion?
My first choice would be for the teacher of heresy to correct his error in the internal and external forums, and begin to teach correct doctrine in its place. But, for whatever reason, most teachers of heresy obstinately persevere in teaching the error. They accept correction from no one, not even from Popes and Ecumenical Councils.
If the person is aware that he has committed an actual mortal sin, by gross negligence in that he taught without first having learned, or in that he taught heresy despite realizing that his teaching contradicted the infallible teaching of the Magisterium, then he should refrain from Communion until he repents and confesses. But realization that one has sinned is not the same as repentance.
One problem is that many teachers of heresy today are very popular. They have approval from many Catholics and even from multiple priests and religious, who fail to recognize that the person is teaching heresy, or who have low regard for magisterial teachings in general, or who adhere to the same heresy being taught. So when the teacher of heresy is accused, many of his supporters come to his defense. Sometimes they even claim that the heretical idea is actually correct understanding of magisterial teaching.
Another problem is that the Bishops have not seen fit to deny Communion to persons obstinately persevering in manifest grave sin, not even to politicians who support abortion and same-sex marriage. The Bishops are also currently reluctant to publicly rebuke any Catholic, especially one who is not a priest, for teaching heresy.
Before the eyes of God, who is no respecter of persons, every teacher of heresy who refuses to accept correction, should be publicly excommunicated and denied Communion, and every adherent of heresy who refuses to repent should not receive Communion. But in the current situation in the Church, very unfortunately, teachers of multiple grave heresies receive Communion, continue to teach heresy without repentance, and continue to have the support of many Catholics.
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