We must now consider apostasy: about which there are two points of inquiry:
(1) Whether apostasy pertains to unbelief?
(2) Whether, on account of apostasy from the faith, subjects are absolved from allegiance to an apostate prince? _______________________
FIRST ARTICLE [II-II, Q. 12, Art. 1]
Whether Apostasy Pertains to Unbelief?
Objection 1: It would seem that apostasy does not pertain to unbelief. For that which is the origin of all sins, does not, seemingly, pertain to unbelief, since many sins there are without unbelief. Now apostasy seems to be the origin of every sin, for it is written (Ecclus. 10:14): "The beginning of the pride of man is apostasy [Douay: 'to fall off'] from God," and further on, (Ecclus. 10:15): "Pride is the beginning of all sin." Therefore apostasy does not pertain to unbelief.
Obj. 2: Further, unbelief is an act of the understanding: whereas apostasy seems rather to consist in some outward deed or utterance, or even in some inward act of the will, for it is written (Prov. 6:12-14): "A man that is an apostate, an unprofitable man walketh with a perverse mouth. He winketh with the eyes, presseth with the foot, speaketh with the finger. With a wicked heart he deviseth evil, and at all times he soweth discord." Moreover if anyone were to have himself circumcised, or to worship at the tomb of Mahomet, he would be deemed an apostate. Therefore apostasy does not pertain to unbelief.
Obj. 3: Further, heresy, since it pertains to unbelief, is a determinate species of unbelief. If then, apostasy pertained to unbelief, it would follow that it is a determinate species of unbelief, which does not seem to agree with what has been said (Q. 10, A. 5). Therefore apostasy does not pertain to unbelief.
On the contrary, It is written (John 6:67): "Many of his disciples went back," i.e. apostatized, of whom Our Lord had said previously (John 6:65): "There are some of you that believe not." Therefore apostasy pertains to unbelief.
I answer that, Apostasy denotes a backsliding from God. This may happen in various ways according to the different kinds of union between man and God. For, in the first place, man is united to God by faith; secondly, by having his will duly submissive in obeying His commandments; thirdly, by certain special things pertaining to supererogation such as the religious life, the clerical state, or Holy Orders. Now if that which follows be removed, that which precedes, remains, but the converse does not hold. Accordingly a man may apostatize from God, by withdrawing from the religious life to which he was bound by profession, or from the Holy Order which he had received: and this is called "apostasy from religious life" or "Orders." A man may also apostatize from God, by rebelling in his mind against the Divine commandments: and though man may apostatize in both the above ways, he may still remain united to God by faith.