Perhaps when we think of excommunication, we think of a cardinal or bishop wagging his finger at a person in some sort of Church court.
Excommunication is typically seen by the media or movies as some sort of punishment that the Catholic Church deals out when she really wants to make sure that an individual is seen as a bad person.
In reality, excommunication is not so much a punishment as a simple statement of fact. It's essentially saying that someone, by their choices, has put themself outside the communion of the Church.
Furthermore, this can happen without an official declaration of the Church in a process called "latae sententiae excommunication."
Automatic excommunication
Fr. Aquinas Guilbeau, OP, wrote an extensive summary of the various sides of excommunication in an article for Aleteia, including this type that is "automatic."
He explains that "the sinner excommunicates himself simply by virtue of a grave act that he freely chooses to perform."
Fr. Aquinas lists some examples of situations when a person automatically puts themselves outside of the Church:
An automatic excommunication is attached to what the Church considers very serious ecclesiastical crimes: apostasy, heresy, and schism; throwing away the Sacred Body or Precious Blood of Christ or retaining either for a sacrilegious purpose; the use of physical force against the pope; a priest’s absolution of someone who is the priest's accomplice in a sin against the sixth commandment (the absolution itself is invalid); a bishop’s consecration of another bishop without a pontifical mandate; a confessor’s direct violation of the seal of confession; the procuring of a completed abortion; and the recording and/or the subsequent divulging of the recording of a sacramental confession.
The Church can investigate the case and make this statement official, but even if the Church does not conduct an investigation, typically the act itself is evidence enough.
It's important to remember that the Church is simply recognizing when a person is no longer in communion with the teachings of the Church.
Fr. Aquinas reiterates that excommunication is meant to be a medicine:
However unpleasant a reality excommunication may be, it has in the Church’s eyes a medicinal quality, and by design it is not intended to be permanent. From this perspective, excommunication is best viewed as the “tough love” Mother Church must sometimes exercise with unfaithful or stubborn souls. She acts, of course, out of her concern for the salvation of souls, which always remains her supreme law.
An excommunicated individual is always welcome back into the loving arms of the Church, but they must first repent of their wrongdoing and recognize their sinfulness.
