Example: A Christian who denies one article of the Creed becomes a heretic and an apostate in a wide sense; if he rejects the entire Creed, he becomes an infidel and an apostate in the strict sense.
(c) Apostasy which extends to infidelity is also twofold: before God and before the Church. The first kind is committed by any person who really had faith, even though unbaptized or not a Catholic; the second kind is committed only by those who were baptized and were Catholics. Examples: A catechumen who accepted Christianity and asked for Baptism, becomes an apostate before God if he abandons his belief and purpose and goes back to paganism. Similarly, a person brought up as a Lutheran becomes an apostate before God, if he abandons all belief in Christianity. But the crime of apostasy of which the Church takes cognizance is the desertion of Christianity by a baptized Catholic.
(d) A Catholic apostatizes from Christianity, either privatively (by merely renouncing all belief in Christ), or contrarily (by taking up some form of unbelief, such as indifferentism or free thought, or by joining some infidel sect, such as Mohammedanism or Confucianism).
836. What was said above regarding the gravity, divisions, penalties and absolution of heresy, can be applied also to apostasy.
887. As to the comparative gravity of sins of apostasy, the following should be noted. (a) Apostasy is not a species of sin distinct from heresy, since both are essentially the same in malice, being rejections of the authority of divine revelation; but it is a circumstance that aggravates the malice of unbelief, since it is more sweeping than heresy (see 822, 824). (b) Apostasy into one form of infidelity is not specifically different from apostasy into another, but the form of infidelity is an aggravating or extenuating circumstance. Example: Paganism is further from faith than Mohammedanism; atheism further than paganism.
838. Could one ever have a just reason for abandoning the Catholic Church or remaining outside its faith? (a) Objectively speaking, there can never be a just cause for giving up Catholicism or for refusing to embrace it. For the Catholic Church is the only true Church, and it is the will of Christ that all should join it. (b) Subjectively speaking, there may be a just cause for leaving or not entering the Church, namely, the fact that a person, ignorant in this matter but in good faith, believes that the Catholic Church is not the true Church. For one is obliged to follow an erroneous conscience, and, if the error is invincible, one is excused from sin (see 581-583). Examples: A Protestant taught to believe that the teachings of the Church are idolatrous, superstitious and absurd, is not blamed for not accepting them. A Catholic, poorly instructed in religion and thrown in with non-Catholic and anti-Catholic associates, might become really persuaded, and without sinning against faith itself, that it was his duty to become a Protestant.
839. Apostasy is committed not only by those who leave the Church and join some contrary religion (e.g., Mormonism), but also by those who, while professing to be Catholics, assent to the non-Catholic principles of some society that claims to be philosophical, charitable, economic, patriotic, etc. Much more are those apostates who join societies that openly conspire against the Church. Such are: (a) Societies that are really non-Catholic sects, because they have an infidel or heretical creed—e.g., Freemasonry (which, according to its own authorities, is a brotherhood based on Egyptian mysteries and claiming superiority to Christianity), Theosophy (which is a conglomeration of nonsensical ideas about the Deity, Christ and Redemption), the Red International, whose aims are the destruction of property rights, etc; (b) Societies that are anti-Catholic sects, because their creed is hatred of the Church—e.g., the Orangemen’s Society, the Grand Orient, the Ku Klux Klan, Junior Order, etc.
840. The Sin of Doubt.—Faith as explained above must be firm assent, excluding doubt (see 752, 799), and hence the saying: “He who doubts is an unbeliever.” The word “doubt,” however, has many meanings, and in some of those meanings it is not opposed to firm assent, or has not the voluntariness or acceptance of error that the unbelief of heresy or infidelity includes. To begin with, doubt is either methodical or real.
(a) Methodical doubt in matters of faith is an inquiry into the motives of credibility of religion and the reasons that support dogma, made by one who has not the slightest fear that reason or science can ever contradict faith, but who consults them for the purpose of clarifying his knowledge and of strengthening his own faith or that of others. This kind of doubt is employed by St. Thomas Aquinas, who questions about each dogma in turn (e.g., “Whether God is good”), and examines the objections of unbelievers against it; but unlike his namesake, the doubting Apostle, he does not withhold assent until reason has answered the objectors, but answers his own questions by an act of faith: “In spite of all difficulties, God is good, for His Word says: ‘The Lord is good to them that hope in Him, to the soul that seeketh Him’ (Lament, iii. 25).”
(b) Real doubt, on the contrary, entertains fears that the teachings of revelation or of the Church may be untrue, or that the opposite teachings may be true.