Is a person only considered a heretic if they intentionally reject truths of the faith?
2089 Incredulity is the neglect of revealed truth or the willful refusal to assent to it. "Heresy is the obstinate post-baptismal denial of some truth which must be believed with divine and catholic faith, or it is likewise an obstinate doubt concerning the same; apostasy is the total repudiation of the Christian faith; schism is the refusal of submission to the Roman Pontiff or of communion with the members of the Church subject to him." (Catechism of the Catholic Church)
817 In fact, "in this one and only Church of God from its very beginnings there arose certain rifts, which the Apostle strongly censures as damnable. But in subsequent centuries much more serious dissensions appeared and large communities became separated from full communion with the Catholic Church - for which, often enough, men of both sides were to blame."269 The ruptures that wound the unity of Christ’s Body - here we must distinguish heresy, apostasy, and schism270 - do not occur without human sin:
Where there are sins, there are also divisions, schisms, heresies, and disputes. Where there is virtue, however, there also are harmony and unity, from which arise the one heart and one soul of all believers.271
818 "However, one cannot charge with the sin of the separation those who at present are born into these communities [that resulted from such separation] and in them are brought up in the faith of Christ, and the Catholic Church accepts them with respect and affection as brothers . . . . All who have been justified by faith in Baptism are incorporated into Christ; they therefore have a right to be called Christians, and with good reason are accepted as brothers in the Lord by the children of the Catholic Church."272 (CCC)
A heretic is someone who takes part of the truth and makes it the whole truth. For example, believing that Jesus is only a man denies the truth of the incarnation: Jesus is fully God and fully man. True: Jesus is man. False: Jesus is only man.
I was going to answer this question with a quote from the Catechism of the Catholic Church but I see that someone else has already gotten to that! Kudos to them!
That said, the Compendium of the Catechism of the Catholic Church does mention heresy here:
442. What is implied in the affirmation of God: “I am the Lord your God” (Exodus 20:2)?
This means that the faithful must guard and activate the three theological virtues and must avoid sins which are opposed to them. Faith believes in God and rejects everything that is opposed to it, such as, deliberate doubt, unbelief, heresy, apostasy, and schism. Hope trustingly awaits the blessed vision of God and his help, while avoiding despair and presumption. * Charity* loves God above all things and therefore repudiates indifference, ingratitude, lukewarmness, sloth or spiritual indolence, and that hatred of God which is born of pride.
Historically the Church has also used this term in a broader sense to refer those who adhere to a heresy, even if they do so innocently, rather than by a perverse act of the will. More recently, the Church has used the more restrictive sense, as noted in the posts above. Some people are confused by this. But this sense isn’t new either–St. Augustine used it this way, for example:
[quote=St. Augustine]But though the doctrine which men hold be false and perverse, if they do not maintain it with passionate obstinacy, especially when they have not devised it by the rashness of their own presumption, but have accepted it from parents who had been misguided and had fallen into error, and if they are with anxiety seeking the truth, and are prepared to be set right when they have found it, such men are not to be counted heretics.
Also, some challenge the idea in CCC 818 that ahs posted above, that says those born into such communities should not be charged with the sin of separation, but this reasoning is also nothing new. Back in the 1800s, the famous british bishop, Cardinal Henry Edward Manning, explained how this idea applied to the Anglicans in his country, but his reasoning could also apply to others who have been born into old separations:
[quote=Cardinal Manning, On the Workings of the Holy Spirit in the Church of England]The Church teaches that men may be inculpably out of its pale. Now they are inculpably out of it who are, and have always been, either physically or morally unable to see their obligation to submit to it. And they only are culpably out of it who are both physically and morally able to know that it is God’s will they should submit to the Church; and either knowing it will not obey that knowledge, or, not knowing it, are culpable for that ignorance. I will say, then, that we hopefully apply this benign law of our Divine Master as far as possible to the English people. First, it is applicable in the letter to the whole multitude of those baptised persons who are under the age of reason. Secondly, to all who are in good faith, of whatsoever age they be: such as a great many of the poor and unlettered, to whom it is often physically, and very often morally, impossible to judge which is the true revelation or the true Church of God. I say physically, because in these three hundred years the Catholic Church has been so swept off the face of England that nine or ten generations of men have lived and died without the Faith being so much as proposed to them, or the Church ever visible to them; and I say morally, because the great majority of the poor, from lifelong prejudice, are often incapable of judging in questions so removed from the primary truths of conscience and Christianity. Of such simple persons it may be said that infantibus cequiparanttir, they are to be classed morally with infants. Again, to these may be added the unlearned in all classes, among whom many have no contact with the Catholic Church, or with Catholic books. Under this head will come a great number of wives and daughters, whose freedom of religious inquiry and religious thought is unjustly limited or suspended by the authority of parents and husbands. Add, lastly, the large class who have been studiously brought up, with all the dominant authority of the English tradition of three hundred years, to believe sincerely, and without a doubt, that the Catholic Church is corrupt, has changed the doctrines of the Faith, and that the author of the Reformation is the Spirit of holiness and truth. It may seem incredible to some that such an illusion exists. But it is credible to me, because for nearly forty years of my life I was fully possessed by this erroneous belief. To all such persons it is morally difficult in no small degree to discover the falsehood of this illusion. All the better parts of their nature are engaged in its support: dutifulness, self-mistrust, submission, respect for others older, better, more learned than themselves, all combine to form a false conscience, and the duty to refuse to hear anything against “the religion of their fathers,” “the Church of their baptism,” or to read anything which could unsettle them. Such people are told that it is their duty to extinguish a doubt against the Church of England, as they would extinguish a temptation against their virtue. A conscience so subdued and held in subjection exercises true virtues upon a false object, and renders to a human authority the submissive trust which is due only to the Divine voice of the Church of God.
Still further, I believe that the people of England were not all guilty of the first acts of heresy and schism by which they were separated from the Catholic unity and faith. They were robbed of it. In many places they rose in arms for it. The children, the poor, the unlearned at that time, were certainly innocent: much more the next generation. They were born into a state of privation. They knew no better. No choice was before them. They made no perverse act of the will in remaining where they were born. Every successive generation was still less culpable, in proportion as they were born into a greater privation, and under the dominion of a tradition of error already grown strong. For three centuries they have been born further and further out of the truth, and their culpability is perpetually diminishing; and as they were passively borne onward in the course of the English separation, the moral responsibility for the past is proportionately less.
To expand on Genesis’ very good answer above, we would call a person who believes in a falsehood that touches on faith and morals for non-culpable reasons (the clearest example would be a tribal person who, in good faith, subscribes to the tenets of the false primitive religion of their tribe, having never come into contact with the Catholic faith) a “material heretic,” i.e., because they are doing the stuff heresy is made of. They wouldn’t become a “formal heretic” until and unless they cross the line into positively rejecting truths revealed to them.
As has been pointed out, too, “heresy” does not require outright rejection. It is sufficient to sustain “obstinate … doubt” about it, i.e., a refusal to adhere to a teaching with the level of assent it demands. For instance, if I said “I guess I’m OK with the Church’s teachings on the impossibility of ordaining women to the priesthood, but I wouldn’t mind if that teaching changed,” I’d probably be entertaining doubts about a teaching that requires full assent of faith.
I heard that a material heretic is someone who unknowingly believes in things that conflict with Church teaching. A lot of the more lax Catholics are like that. Then there are people that know they are going against Church teaching and beliefs. I can’t remember what they’re called. The latter is far more serious than the former.
Your are talking about a “material heretic” vs a “formal heretic.” As you said, a material heretic is someone that doesn’t know he is following heretical beliefs. A formal heretic is a person who knows he is following such a belief.
And, IIRC, only formal heresy is a mortal sin. Material heresy is due to ignorance, but can be dangerous to others who are also ignorant if the person spreads it. One is usually only considered in formal heresy, if after attempted correction by the Church, he (the vast majority of condemned formal heretics in Church history have been clergy; their followers were usually considered material heretics because in most cases, the followers of formal heretics didn’t know that they were being taught heresy - though it is possible that a woman could be a formal heretic).
If a person is baptized, and they obstinately reject a single truth of the Catholic faith after being informed about that Catholic truth, then they are a heretic.
God bless you, and Mary keep you…