Formal vs. Material Heresy

Heresy is a mortal sin. As stated by the Baltimore Catechism: "The denial of only one article of faith will make a person a heretic and guilty of mortal sin, because the Holy Scripture says: 'Whosoever shall keep the whole law but offend in one point is become guilty of all'" (Q. 1171). Sadly, there are many in the Church today who are heretics - many in the hierarchy who are formal heretics and many of faithful lay Catholics in the pews who are led astray into material heresy.

The Catholic Church rightfully asserts and teaches that its doctrines are the authoritative understandings of the Faith taught by our Savior Jesus Christ and that the Holy Ghost protects the Church from falling into error when teaching these doctrines. To deny one or more of those doctrines, therefore, is to deny the faith of Christ entirely. Heresy is both the non-orthodox belief itself, and the act of holding to that belief. However, the Church makes several distinctions as to the seriousness of an individual heterodoxy and its closeness to true heresy. Only a belief that directly contravenes an Article of Faith, or that has been explicitly rejected by the Church, is labelled as actual "heresy."

An important distinction is that between formal and material heresy.

The difference is one of the heretic's subjective belief about his opinion. The heretic who is aware that his belief is at odds with Catholic teaching and yet continues to cling to his belief pertinaciously is a formal heretic. This sort of heresy is sinful because in this case the heretic knowingly holds an opinion that, in the words of the first edition of the Catholic Encyclopedia, "is destructive of the virtue of Christian faith ... disturbs the unity, and challenges the Divine authority, of the Church" and "strikes at the very source of faith." Material heresy, on the other hand, means that the individual is unaware that his heretical opinion denies, in the words of Canon 751, "some truth which is to be believed by divine and Catholic faith." The opinion of a material heretic may produce the same objective results as formal heresy, but because of his ignorance he commits no sin by holding it. The penalty for a baptised Catholic above the age of 18 who obstinately, publicly, and voluntarily manifests his or her adherence to an objective heresy is automatic excommunication ("latae sententiae") according to Can. 1364 par.1 CIC.

A belief that the church has not directly rejected, or that is at variance with less important church teachings, is given the label, sententia haeresi proxima, meaning "opinion approaching heresy." A theological argument, belief, or theory that does not constitute heresy in itself, but which leads to conclusions which might be held to do so, is termed propositio theologice erronea, or "erroneous theological proposition". Finally, if the theological position only suggests but does not necessarily lead to a doctrinal conflict, it might be given the even milder label of sententia de haeresi suspecta, haeresim sapiens, meaning "opinion suspected, or savoring, of heresy."

Source: Heresy in the Catholic Church