from
ewtn.com/expert/answers/heresy_schism_apostasy.htm
"Heresy, Schism and Apostasy
Definitions The
Catechism of the Catholic Church defines these three sins against the faith in this way:
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."
Code of Canon Law c.751]
The Church’s moral theology has always distinguished between objective or *material *sin and
formal sin. The person who holds something contrary to the Catholic faith is materially a heretic. They possess the matter of heresy, theological error.
Thus, prior to the Second Vatican Council it was quite common to speak of non-Catholic Christians as heretics, since many of their doctrines are objectively contrary to Catholic teaching. This theological distinction remains true, though in keeping with the pastoral charity of the Council today we use the term heretic only to describe those who willingly embrace what they know to be contrary to revealed truth. Such persons are
formally (in their conscience before God) guilty of heresy. Thus, the person who is objectively in heresy is not
formally guilty of heresy if 1) their ignorance of the truth is due to their upbringing in a particular religious tradition (to which they may even be scrupulously faithful), and 2) they are not morally responsible for their ignorance of the truth. This is the principle of
invincible ignorance, which Catholic theology has always recognized as excusing before God.
ETC…"