Summa Th. II-II EN Qu.11


We must now consider heresy: under which head there are four points of inquiry:

(1) Whether heresy is a kind of unbelief?

(2) Of the matter about which it is;

(3) Whether heretics should be tolerated?

(4) Whether converts should be received?

Whether heresy is a species of unbelief?

Objection: 1. It would seem that heresy is not a species of unbelief. For unbelief is in the understanding, as stated above (Question [10], Article [2]). Now heresy would seem not to pertain to the understanding, but rather to the appetitive power; for Jerome says on Ga 5,19: [*Cf. Decretals xxiv, qu. iii, cap. 27] "The works of the flesh are manifest: Heresy is derived from a Greek word meaning choice, whereby a man makes choice of that school which he deems best." But choice is an act of the appetitive power, as stated above (FS, Question [13], Article [1]). Therefore heresy is not a species of unbelief.
2. Further, vice takes its species chiefly from its end; hence the Philosopher says (Ethic. v, 2) that "he who commits adultery that he may steal, is a thief rather than an adulterer." Now the end of heresy is temporal profit, especially lordship and glory, which belong to the vice of pride or covetousness: for Augustine says (De Util. Credendi i) that "a heretic is one who either devises or follows false and new opinions, for the sake of some temporal profit, especially that he may lord and be honored above others." Therefore heresy is a species of pride rather than of unbelief.
3. Further, since unbelief is in the understanding, it would seem not to pertain to the flesh. Now heresy belongs to the works of the flesh, for the Apostle says (Ga 5,19): "The works of the flesh are manifest, which are fornication, uncleanness," and among the others, he adds, "dissensions, sects," which are the same as heresies. Therefore heresy is not a species of unbelief.

On the contrary Falsehood is contrary to truth. Now a heretic is one who devises or follows false or new opinions. Therefore heresy is opposed to the truth, on which faith is founded; and consequently it is a species of unbelief.
I answer that The word heresy as stated in the first objection denotes a choosing. Now choice as stated above (FS, Question [13], Article [3]) is about things directed to the end, the end being presupposed. Now, in matters of faith, the will assents to some truth, as to its proper good, as was shown above (Question [4], Article [3]): wherefore that which is the chief truth, has the character of last end, while those which are secondary truths, have the character of being directed to the end.Now, whoever believes, assents to someone's words; so that, in every form of unbelief, the person to whose words assent is given seems to hold the chief place and to be the end as it were; while the things by holding which one assents to that person hold a secondary place. Consequently he that holds the Christian faith aright, assents, by his will, to Christ, in those things which truly belong to His doctrine.Accordingly there are two ways in which a man may deviate from the rectitude of the Christian faith. First, because he is unwilling to assent to Christ: and such a man has an evil will, so to say, in respect of the very end. This belongs to the species of unbelief in pagans and Jews. Secondly, because, though he intends to assent to Christ, yet he fails in his choice of those things wherein he assents to Christ, because he chooses not what Christ really taught, but the suggestions of his own mind.Therefore heresy is a species of unbelief, belonging to those who profess the Christian faith, but corrupt its dogmas.

Reply to Objection: 1. Choice regards unbelief in the same way as the will regards faith, as stated above.
2. Vices take their species from their proximate end, while, from their remote end, they take their genus and cause. Thus in the case of adultery committed for the sake of theft, there is the species of adultery taken from its proper end and object; but the ultimate end shows that the act of adultery is both the result of the theft, and is included under it, as an effect under its cause, or a species under its genus, as appears from what we have said about acts in general (FS, Question [18], Article [7]). Wherefore, as to the case in point also, the proximate end of heresy is adherence to one's own false opinion, and from this it derives its species, while its remote end reveals its cause, viz. that it arises from pride or covetousness.
3. Just as heresy is so called from its being a choosing [*From the Greek (airein) [hairein], to cut off], so does sect derive its name from its being a cutting off [secando], as Isidore states (Etym. viii, 3). Wherefore heresy and sect are the same thing, and each belongs to the works of the flesh, not indeed by reason of the act itself of unbelief in respect of its proximate object, but by reason of its cause, which is either the desire of an undue end in which way it arises from pride or covetousness, as stated in the second objection, or some illusion of the imagination (which gives rise to error, as the Philosopher states in Metaph. iv; Ed. Did. iii, 5), for this faculty has a certain connection with the flesh, in as much as its act is independent on a bodily organ.

Whether heresy is properly about matters of faith?

Objection: 1. It would seem that heresy is not properly about matters of faith. For just as there are heresies and sects among Christians, so were there among the Jews, and Pharisees, as Isidore observes (Etym. viii, 3,4,5). Now their dissensions were not about matters of faith. Therefore heresy is not about matters of faith, as though they were its proper matter.
2. Further, the matter of faith is the thing believed. Now heresy is not only about things, but also about works, and about interpretations of Holy Writ. For Jerome says on Ga 5,20 that "whoever expounds the Scriptures in any sense but that of the Holy Ghost by Whom they were written, may be called a heretic, though he may not have left the Church": and elsewhere he says that "heresies spring up from words spoken amiss." [*St. Thomas quotes this saying elsewhere, in Sent. iv, D, 13, and TP, Question [16], Article [8], but it is not to be found in St. Jerome's works.] Therefore heresy is not properly about the matter of faith.
3. Further, we find the holy doctors differing even about matters pertaining to the faith, for example Augustine and Jerome, on the question about the cessation of the legal observances: and yet this was without any heresy on their part. Therefore heresy is not properly about the matter of faith.

On the contrary Augustine says against the Manichees [*Cf. De Civ. Dei xviii, 51]: "In Christ's Church, those are heretics, who hold mischievous and erroneous opinions, and when rebuked that they may think soundly and rightly, offer a stubborn resistance, and, refusing to mend their pernicious and deadly doctrines, persist in defending them." Now pernicious and deadly doctrines are none but those which are contrary to the dogmas of faith, whereby "the just man liveth" (Rm 1,17). Therefore heresy is about matters of faith, as about its proper matter.
I answer that We are speaking of heresy now as denoting a corruption of the Christian faith. Now it does not imply a corruption of the Christian faith, if a man has a false opinion in matters that are not of faith, for instance, in questions of geometry and so forth, which cannot belong to the faith by any means; but only when a person has a false opinion about things belonging to the faith.Now a thing may be of the faith in two ways, as stated above (FP, Question [32], Article [4]; FS, Question [1], Article [6], ad 1; FS, Question [2], Article [5]), in one way, directly and principally, e.g. the articles of faith; in another way, indirectly and secondarily, e.g. those matters, the denial of which leads to the corruption of some article of faith; and there may be heresy in either way, even as there can be faith.

Reply to Objection: 1. Just as the heresies of the Jews and Pharisees were about opinions relating to Judaism or Pharisaism, so also heresies among Christians are about matter touching the Christian faith.
2. A man is said to expound Holy Writ in another sense than that required by the Holy Ghost, when he so distorts the meaning of Holy Writ, that it is contrary to what the Holy Ghost has revealed. Hence it is written (Ez 13,6) about the false prophets: "They have persisted to confirm what they have said," viz. by false interpretations of Scripture. Moreover a man professes his faith by the words that he utters, since confession is an act of faith, as stated above (Question [3], Article [1]). Wherefore inordinate words about matters of faith may lead to corruption of the faith; and hence it is that Pope Leo says in a letter to Proterius, Bishop of Alexandria: "The enemies of Christ's cross lie in wait for our every deed and word, so that, if we but give them the slightest pretext, they may accuse us mendaciously of agreeing with Nestorius."
3. As Augustine says (Ep. xliii) and we find it stated in the Decretals (xxiv, qu. 3, can. Dixit Apostolus): "By no means should we accuse of heresy those who, however false and perverse their opinion may be, defend it without obstinate fervor, and seek the truth with careful anxiety, ready to mend their opinion, when they have found the truth," because, to wit, they do not make a choice in contradiction to the doctrine of the Church. Accordingly, certain doctors seem to have differed either in matters the holding of which in this or that way is of no consequence, so far as faith is concerned, or even in matters of faith, which were not as yet defined by the Church; although if anyone were obstinately to deny them after they had been defined by the authority of the universal Church, he would be deemed a heretic. This authority resides chiefly in the Sovereign Pontiff. For we read [*Decret. xxiv, qu. 1, can. Quoties]: "Whenever a question of faith is in dispute, I think, that all our brethren and fellow bishops ought to refer the matter to none other than Peter, as being the source of their name and honor, against whose authority neither Jerome nor Augustine nor any of the holy doctors defended their opinion." Hence Jerome says (Exposit. Symbol [*Among the supposititious works of St. Jerome]): "This, most blessed Pope, is the faith that we have been taught in the Catholic Church. If anything therein has been incorrectly or carelessly expressed, we beg that it may be set aright by you who hold the faith and see of Peter. If however this, our profession, be approved by the judgment of your apostleship, whoever may blame me, will prove that he himself is ignorant, or malicious, or even not a catholic but a heretic."

Whether heretics ought to be tolerated?

Objection: 1. It seems that heretics ought to be tolerated. For the Apostle says (2Tm 2,24-25): "The servant of the Lord must not wrangle . . . with modesty admonishing them that resist the truth, if peradventure God may give them repentance to know the truth, and they may recover themselves from the snares of the devil." Now if heretics are not tolerated but put to death, they lose the opportunity of repentance. Therefore it seems contrary to the Apostle's command.
2. Further, whatever is necessary in the Church should be tolerated. Now heresies are necessary in the Church, since the Apostle says (1Co 11,19): "There must be . . . heresies, that they . . . who are reproved, may be manifest among you." Therefore it seems that heretics should be tolerated.
3. Further, the Master commanded his servants (Mt 13,30) to suffer the cockle "to grow until the harvest," i.e. the end of the world, as a gloss explains it. Now holy men explain that the cockle denotes heretics. Therefore heretics should be tolerated.

On the contrary The Apostle says (Titus 3:10,11): "A man that is a heretic, after the first and second admonition, avoid: knowing that he, that is such an one, is subverted."
I answer that With regard to heretics two points must be observed: one, on their own side; the other, on the side of the Church. On their own side there is the sin, whereby they deserve not only to be separated from the Church by excommunication, but also to be severed from the world by death. For it is a much graver matter to corrupt the faith which quickens the soul, than to forge money, which supports temporal life. Wherefore if forgers of money and other evil-doers are forthwith condemned to death by the secular authority, much more reason is there for heretics, as soon as they are convicted of heresy, to be not only excommunicated but even put to death.On the part of the Church, however, there is mercy which looks to the conversion of the wanderer, wherefore she condemns not at once, but "after the first and second admonition," as the Apostle directs: after that, if he is yet stubborn, the Church no longer hoping for his conversion, looks to the salvation of others, by excommunicating him and separating him from the Church, and furthermore delivers him to the secular tribunal to be exterminated thereby from the world by death. For Jerome commenting on Ga 5,9, "A little leaven," says: "Cut off the decayed flesh, expel the mangy sheep from the fold, lest the whole house, the whole paste, the whole body, the whole flock, burn, perish, rot, die. Arius was but one spark in Alexandria, but as that spark was not at once put out, the whole earth was laid waste by its flame."

Reply to Objection: 1. This very modesty demands that the heretic should be admonished a first and second time: and if he be unwilling to retract, he must be reckoned as already "subverted," as we may gather from the words of the Apostle quoted above.
2. The profit that ensues from heresy is beside the intention of heretics, for it consists in the constancy of the faithful being put to the test, and "makes us shake off our sluggishness, and search the Scriptures more carefully," as Augustine states (De Gen. cont. Manich. i, 1). What they really intend is the corruption of the faith, which is to inflict very great harm indeed. Consequently we should consider what they directly intend, and expel them, rather than what is beside their intention, and so, tolerate them.
3. According to Decret. (xxiv, qu. iii, can. Notandum), "to be excommunicated is not to be uprooted." A man is excommunicated, as the Apostle says (1Co 5,5) that his "spirit may be saved in the day of Our Lord." Yet if heretics be altogether uprooted by death, this is not contrary to Our Lord's command, which is to be understood as referring to the case when the cockle cannot be plucked up without plucking up the wheat, as we explained above (Question [10], Article [8], ad 1), when treating of unbelievers in general.

Whether the Church should receive those who return from heresy?

Objection: 1. It would seem that the Church ought in all cases to receive those who return from heresy. For it is written (Jr 3,1) in the person of the Lord: "Thou hast prostituted thyself to many lovers; nevertheless return to Me saith the Lord." Now the sentence of the Church is God's sentence, according to Dt 1,17: "You shall hear the little as well as the great: neither shall you respect any man's person, because it is the judgment of God." Therefore even those who are guilty of the prostitution of unbelief which is spiritual prostitution, should be received all the same.
2. Further, Our Lord commanded Peter (Mt 18,22) to forgive his offending brother "not" only "till seven times, but till seventy times seven times," which Jerome expounds as meaning that "a man should be forgiven, as often as he has sinned." Therefore he ought to be received by the Church as often as he has sinned by falling back into heresy.
3. Further, heresy is a kind of unbelief. Now other unbelievers who wish to be converted are received by the Church. Therefore heretics also should be received.

On the contrary The Decretal Ad abolendam (De Haereticis, cap. ix) says that "those who are found to have relapsed into the error which they had already abjured, must be left to the secular tribunal." Therefore they should not be received by the Church.
I answer that In obedience to Our Lord's institution, the Church extends her charity to all, not only to friends, but also to foes who persecute her, according to Mt 5,44: "Love your enemies; do good to them that hate you." Now it is part of charity that we should both wish and work our neighbor's good. Again, good is twofold: one is spiritual, namely the health of the soul, which good is chiefly the object of charity, since it is this chiefly that we should wish for one another. Consequently, from this point of view, heretics who return after falling no matter how often, are admitted by the Church to Penance whereby the way of salvation is opened to them.The other good is that which charity considers secondarily, viz. temporal good, such as life of the body, worldly possessions, good repute, ecclesiastical or secular dignity, for we are not bound by charity to wish others this good, except in relation to the eternal salvation of them and of others. Hence if the presence of one of these goods in one individual might be an obstacle to eternal salvation in many, we are not bound out of charity to wish such a good to that person, rather should we desire him to be without it, both because eternal salvation takes precedence of temporal good, and because the good of the many is to be preferred to the good of one. Now if heretics were always received on their return, in order to save their lives and other temporal goods, this might be prejudicial to the salvation of others, both because they would infect others if they relapsed again, and because, if they escaped without punishment, others would feel more assured in lapsing into heresy. For it is written (Qo 8,11): "For because sentence is not speedily pronounced against the evil, the children of men commit evils without any fear."For this reason the Church not only admits to Penance those who return from heresy for the first time, but also safeguards their lives, and sometimes by dispensation, restores them to the ecclesiastical dignities which they may have had before, should their conversion appear to be sincere: we read of this as having frequently been done for the good of peace. But when they fall again, after having been received, this seems to prove them to be inconstant in faith, wherefore when they return again, they are admitted to Penance, but are not delivered from the pain of death.

Reply to Objection: 1. In God's tribunal, those who return are always received, because God is a searcher of hearts, and knows those who return in sincerity. But the Church cannot imitate God in this, for she presumes that those who relapse after being once received, are not sincere in their return; hence she does not debar them from the way of salvation, but neither does she protect them from the sentence of death.
2. Our Lord was speaking to Peter of sins committed against oneself, for one should always forgive such offenses and spare our brother when he repents. These words are not to be applied to sins committed against one's neighbor or against God, for it is not left to our discretion to forgive such offenses, as Jerome says on Mt 18,15, "If thy brother shall offend against thee." Yet even in this matter the law prescribes limits according as God's honor or our neighbor's good demands.
3. When other unbelievers, who have never received the faith are converted, they do not as yet show signs of inconstancy in faith, as relapsed heretics do; hence the comparison fails.


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?

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 (Si 10,14): "The beginning of the pride of man is apostasy [Douay: 'to fall off'] from God," and further on, (Si 10,15): "Pride is the beginning of all sin." Therefore apostasy does not pertain to unbelief.
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 (Pr 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.
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 (Question [10], Article [5]). Therefore apostasy does not pertain to unbelief.

On the contrary It is written (Jn 6,67): "Many of his disciples went back," i.e. apostatized, of whom Our Lord had said previously (Jn 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.But if he give up the faith, then he seems to turn away from God altogether: and consequently, apostasy simply and absolutely is that whereby a man withdraws from the faith, and is called "apostasy of perfidy." In this way apostasy, simply so called, pertains to unbelief.

Reply to Objection: 1. This objection refers to the second kind of apostasy, which denotes an act of the will in rebellion against God's commandments, an act that is to be found in every mortal sin.
2. It belongs to faith not only that the heart should believe, but also that external words and deeds should bear witness to the inward faith, for confession is an act of faith. In this way too, certain external words or deeds pertain to unbelief, in so far as they are signs of unbelief, even as a sign of health is said itself to be healthy. Now although the authority quoted may be understood as referring to every kind of apostate, yet it applies most truly to an apostate from the faith. For since faith is the first foundation of things to be hoped for, and since, without faith it is "impossible to please God"; when once faith is removed, man retains nothing that may be useful for the obtaining of eternal salvation, for which reason it is written (Pr 6,12): "A man that is an apostate, an unprofitable man": because faith is the life of the soul, according to Rm 1,17: "The just man liveth by faith." Therefore, just as when the life of the body is taken away, man's every member and part loses its due disposition, so when the life of justice, which is by faith, is done away, disorder appears in all his members. First, in his mouth, whereby chiefly his mind stands revealed; secondly, in his eyes; thirdly, in the instrument of movement; fourthly, in his will, which tends to evil. The result is that "he sows discord," endeavoring to sever others from the faith even as he severed himself.
3. The species of a quality or form are not diversified by the fact of its being the term "wherefrom" or "whereto" of movement: on the contrary, it is the movement that takes its species from the terms. Now apostasy regards unbelief as the term "whereto" of the movement of withdrawal from the faith; wherefore apostasy does not imply a special kind of unbelief, but an aggravating circumstance thereof, according to 2P 2,21: "It had been better for them not to know the truth [Vulg.: 'the way of justice'], than after they had known it, to turn back."

Whether a prince forfeits his dominion over his subjects, on account of apostasy from the faith, so that they no longer owe him allegiance?

Objection: 1. It would seem that a prince does not so forfeit his dominion over his subjects, on account of apostasy from the faith, that they no longer owe him allegiance. For Ambrose [*St. Augustine, Super Ps 124,3] says that the Emperor Julian, though an apostate, nevertheless had under him Christian soldiers, who when he said to them, "Fall into line for the defense of the republic," were bound to obey. Therefore subjects are not absolved from their allegiance to their prince on account of his apostasy.
2. Further, an apostate from the faith is an unbeliever. Now we find that certain holy men served unbelieving masters; thus Joseph served Pharaoh, Daniel served Nabuchodonosor, and Mardochai served Assuerus. Therefore apostasy from the faith does not release subjects from allegiance to their sovereign.
3. Further, just as by apostasy from the faith, a man turns away from God, so does every sin. Consequently if, on account of apostasy from the faith, princes were to lose their right to command those of their subjects who are believers, they would equally lose it on account of other sins: which is evidently not the case. Therefore we ought not to refuse allegiance to a sovereign on account of his apostatizing from the faith.

On the contrary Gregory VII says (Council, Roman V): "Holding to the institutions of our holy predecessors, we, by our apostolic authority, absolve from their oath those who through loyalty or through the sacred bond of an oath owe allegiance to excommunicated persons: and we absolutely forbid them to continue their allegiance to such persons, until these shall have made amends." Now apostates from the faith, like heretics, are excommunicated, according to the Decretal [*Extra, De Haereticis, cap. Ad abolendam]. Therefore princes should not be obeyed when they have apostatized from the faith.
I answer that As stated above (Question [10], Article [10]), unbelief, in itself, is not inconsistent with dominion, since dominion is a device of the law of nations which is a human law: whereas the distinction between believers and unbelievers is of Divine right, which does not annul human right. Nevertheless a man who sins by unbelief may be sentenced to the loss of his right of dominion, as also, sometimes, on account of other sins.Now it is not within the competency of the Church to punish unbelief in those who have never received the faith, according to the saying of the Apostle (1Co 5,12): "What have I to do to judge them that are without?" She can, however, pass sentence of punishment on the unbelief of those who have received the faith: and it is fitting that they should be punished by being deprived of the allegiance of their subjects: for this same allegiance might conduce to great corruption of the faith, since, as was stated above (Article [1], Objection [2]), "a man that is an apostate . . . with a wicked heart deviseth evil, and . . . soweth discord," in order to sever others from the faith. Consequently, as soon as sentence of excommunication is passed on a man on account of apostasy from the faith, his subjects are "ipso facto" absolved from his authority and from the oath of allegiance whereby they were bound to him.

Reply to Objection: 1. At that time the Church was but recently instituted, and had not, as yet, the power of curbing earthly princes; and so she allowed the faithful to obey Julian the apostate, in matters that were not contrary to the faith, in order to avoid incurring a yet greater danger.
2. As stated in the article, it is not a question of those unbelievers who have never received the faith.
3. Apostasy from the faith severs man from God altogether, as stated above (Article [1]), which is not the case in any other sin.


We must now consider the sin of blasphemy, which is opposed to the confession of faith; and (1) blasphemy in general, (2) that blasphemy which is called the sin against the Holy Ghost.

Under the first head there are four points of inquiry:

(1) Whether blasphemy is opposed to the confession of faith?

(2) Whether blasphemy is always a mortal sin?

(3) Whether blasphemy is the most grievous sin?

(4) Whether blasphemy is in the damned?

Whether blasphemy is opposed to the confession of faith?

Objection: 1. It would seem that blasphemy is not opposed to the confession of faith. Because to blaspheme is to utter an affront or insult against the Creator. Now this pertains to ill-will against God rather than to unbelief. Therefore blasphemy is not opposed to the confession of faith.
2. Further, on Ep 4,31, "Let blasphemy . . . be put away from you," a gloss says, "that which is committed against God or the saints." But confession of faith, seemingly, is not about other things than those pertaining to God, Who is the object of faith. Therefore blasphemy is not always opposed to the confession of faith.
3. Further, according to some, there are three kinds of blasphemy. The first of these is when something unfitting is affirmed of God; the second is when something fitting is denied of Him; and the third, when something proper to God is ascribed to a creature, so that, seemingly, blasphemy is not only about God, but also about His creatures. Now the object of faith is God. Therefore blasphemy is not opposed to confession of faith.

On the contrary The Apostle says (1Tm 1,12-13): "I . . . before was a blasphemer and a persecutor," and afterwards, "I did it ignorantly in" my "unbelief." Hence it seems that blasphemy pertains to unbelief.
I answer that The word blasphemy seems to denote the disparagement of some surpassing goodness, especially that of God. Now God, as Dionysius says (Div. Nom. i), is the very essence of true goodness. Hence whatever befits God, pertains to His goodness, and whatever does not befit Him, is far removed from the perfection of goodness which is His Essence. Consequently whoever either denies anything befitting God, or affirms anything unbefitting Him, disparages the Divine goodness.Now this may happen in two ways. In the first way it may happen merely in respect of the opinion in the intellect; in the second way this opinion is united to a certain detestation in the affections, even as, on the other hand, faith in God is perfected by love of Him. Accordingly this disparagement of the Divine goodness is either in the intellect alone, or in the affections also. If it is in thought only, it is blasphemy of the heart, whereas if it betrays itself outwardly in speech it is blasphemy is opposed to confession of faith.

Reply to Objection: 1. He that speaks against God, with the intention of reviling Him, disparages the Divine goodness, not only in respect of the falsehood in his intellect, but also by reason of the wickedness of his will, whereby he detests and strives to hinder the honor due to God, and this is perfect blasphemy.
2. Even as God is praised in His saints, in so far as praise is given to the works which God does in His saints, so does blasphemy against the saints, redound, as a consequence, against God.
3. Properly speaking, the sin of blasphemy is not in this way divided into three species: since to affirm unfitting things, or to deny fitting things of God, differ merely as affirmation and negation. For this diversity does not cause distinct species of habits, since the falsehood of affirmations and negations is made known by the same knowledge, and it is the same ignorance which errs in either way, since negatives are proved by affirmatives, according to Poster. i, 25. Again to ascribe to creatures things that are proper to God, seems to amount to the same as affirming something unfitting of Him, since whatever is proper to God is God Himself: and to ascribe to a creature, that which is proper to God, is to assert that God is the same as a creature.

Summa Th. II-II EN Qu.11