Formal excommunication from the Catholic Church is a rarity.1 However, there are many ways to be excommunicated through one’s actions. Here is the short list of ways that excommunication can occur (even without formal, documented excommunication).
1. Be A Heretic
“[A] species of infidelity in men who, having professed the faith of Christ, corrupt its dogmas.” 2 This is a way, not of rejecting Christianity, but of deviating by choosing select teachings among the whole to believe, while rejecting others. 3
2. Be A Schismatic
A schismatic is one who separates themself from the unity of the Church by refusing to submit to the Pope or those under him according to the hierarchy of the Church. Regardless of adherence to every other law of the Church, rejection of the Supreme Pontif is cause to be named schismatic. 4
3. Be An Apostate
The apostate rejects the entirety of the Catholic faith. Whether he chooses to embrace another, or to align with none at all, he willingly rejects the Truth he knows. This name is not applicable to the ignorant, but to those who knowingly reject Catholicism with full knowledge of the implications. 5