What is heresy?
The word heresy derives from the Greek word αἵρεσις (pronounced hairesis) meaning "choice." Heresy is the formal denial of any defined doctrine of the Catholic faith. In other words, the very first "pro-choice" people were the ancient Christian heretics.
We find Saint Paul using the word in 1 Cor. 11:19 where he writes:
"for there must be heresies (αἱρέσεις) among you in order that those who are genuine among you may be recognized."Saint Peter also speaks of the heretics of the early Church:
"But false prophets also arose among the people,Incidentally, note how Saint Peter specifies the heretics as having previously been Christians. They are described as "denying the Master (i.e. Christ) who bought them [with His precious blood]."
just as there will be false teachers among you, who will secretly bring in destructive heresies (αἱρέσεις), even denying the Master who bought them, bringing upon themselves swift destruction" (2 Peter 2:1).
Saint Ignatius of Antioch speaks of αἱρέσεις or haireseis in the form of theological denials and errors. He calls heresy poison mixed up with something good. Hence, heresy always attaches itself to something good and true and then corrupts it:
I therefore, yet not I, but the love of Jesus Christ, entreat you that ye use Christian nourishment only, and abstain from herbage of a different kind; I mean heresy. For those [that are given to this] mix up Jesus Christ with their own poison, speaking things which are unworthy of credit, like those who administer a deadly drug in sweet wine, which he who is ignorant of does greedily take, with a fatal pleasure31 leading to his own death (Epistle to Trallians 6).According to Catholic canon law, heresy is strictly defined as the obstinate denial or doubt, after Baptism, of a truth ‘which must be believed with divine and catholic faith’ (CIC 1983, can. 751).
This ‘formal’ heresy is a grave sin involving ipso facto excommunication. For example, if I, a baptized Catholic who has formally studied Christology, were to believe that Christ has three natures and not two (divine and human), I would be ipso facto excommunicated.
Catholic theology distinguishes 'formal heresy' from 'material heresy.' Material heresy entails believing heretical doctrines through no fault of one’s own 'in good faith.' For example, if a Baptist grandmother in Arkansas denies infant baptism without having been a Catholic and without having investigated the doctrine, she subscribes to heresy materially and is without fault.
This is a helpful distinction and is in accord with the virtue of charity and the moral law regarding knowledge and consent. It also conforms to Saint Peter's distinction above which describes heretics as purposefully passing from truth to falsity.
Image above: Mary, Exterminatrix of Heresy.