Summa Th. I-II EN Qu.74 a.2
Objection: 1. It would seem that the will alone is the subject of sin. For Augustine says (De Duabus Anim. x, 10) that "no one sins except by the will." Now the subject of sin is the power by which we sin. Therefore the will alone is the subject of sin.
2. Further, sin is an evil contrary to reason. Now good and evil pertaining to reason are the object of the will alone. Therefore the will alone is the subject of sin.
3. Further, every sin is a voluntary act, because, as Augustine states (De Lib. Arb. iii, 18) [*Cf. De Vera Relig. xiv.], "so true is it that every sin is voluntary, that unless it be voluntary, it is no sin at all." Now the acts of the other powers are not voluntary, except in so far as those powers are moved by the will; nor does this suffice for them to be the subject of sin, because then even the external members of the body, which are moved by the will, would be a subject of sin; which is clearly untrue. Therefore the will alone is the subject of sin.
On the contrary Sin is contrary to virtue: and contraries are about one same thing. But the other powers of the soul, besides the will, are the subject of virtues, as stated above (Question ). Therefore the will is not the only subject of sin.
I answer that As was shown above (Article ), whatever is the a principle of a voluntary act is a subject of sin. Now voluntary acts are not only those which are elicited by the will, but also those which are commanded by the will, as we stated above (Question , Article ) in treating of voluntariness. Therefore not only the will can be a subject of sin, but also all those powers which can be moved to their acts, or restrained from their acts, by the will; and these same powers are the subjects of good and evil moral habits, because act and habit belong to the same subject.
Reply to Objection: 1. We do not sin except by the will as first mover; but we sin by the other powers as moved by the will.
2. Good and evil pertain to the will as its proper objects; but the other powers have certain determinate goods and evils, by reason of which they can be the subject of virtue, vice, and sin, in so far as they partake of will and reason.
3. The members of the body are not principles but merely organs of action: wherefore they are compared to the soul which moves them, as a slave who is moved but moves no other. On the other hand, the internal appetitive powers are compared to reason as free agents, because they both act and are acted upon, as is made clear in Polit. i, 3. Moreover, the acts of the external members are actions that pass into external matter, as may be seen in the blow that is inflicted in the sin of murder. Consequently there is no comparison.
Objection: 1. It would seem that there cannot be sin in the sensuality. For sin is proper to man who is praised or blamed for his actions. Now sensuality is common to us and irrational animals. Therefore sin cannot be in the sensuality.
2. Further, "no man sins in what he cannot avoid," as Augustine states (De Lib. Arb. iii, 18). But man cannot prevent the movement of the sensuality from being inordinate, since "the sensuality ever remains corrupt, so long as we abide in this mortal life; wherefore it is signified by the serpent," as Augustine declares (De Trin. xii, 12,13). Therefore the inordinate movement of the sensuality is not a sin.
3. Further, that which man himself does not do is not imputed to him as a sin. Now "that alone do we seem to do ourselves, which we do with the deliberation of reason," as the Philosopher says (Ethic. ix, 8). Therefore the movement of the sensuality, which is without the deliberation of reason, is not imputed to a man as a sin.
On the contrary It is written (Rm 7,19): "The good which I will I do not; but the evil which I will not, that I do": which words Augustine explains (Contra Julian. iii, 26; De Verb. Apost. xii, 2,3), as referring to the evil of concupiscence, which is clearly a movement of the sensuality. Therefore there can be sin in the sensuality.
I answer that As stated above (Articles ,3), sin may be found in any power whose act can be voluntary and inordinate, wherein consists the nature of sin. Now it is evident that the act of the sensuality, or sensitive appetite, is naturally inclined to be moved by the will. Wherefore it follows that sin can be in the sensuality.
Reply to Objection: 1. Although some of the powers of the sensitive part are common to us and irrational animals, nevertheless, in us, they have a certain excellence through being united to the reason; thus we surpass other animals in the sensitive part for as much as we have the powers of cogitation and reminiscence, as stated in the I 78,4. In the same way our sensitive appetite surpasses that of other animals by reason of a certain excellence consisting in its natural aptitude to obey the reason; and in this respect it can be the principle of a voluntary action, and, consequently, the subject of sin.
2. The continual corruption of the sensuality is to be understood as referring to the "fomes," which is never completely destroyed in this life, since, though the stain of original sin passes, its effect remains. However, this corruption of the "fomes" does not hinder man from using his rational will to check individual inordinate movements, if he be presentient to them, for instance by turning his thoughts to other things. Yet while he is turning his thoughts to something else, an inordinate movement may arise about this also: thus when a man, in order to avoid the movements of concupiscence, turns his thoughts away from carnal pleasures, to the considerations of science, sometimes an unpremeditated movement of vainglory will arise. Consequently, a man cannot avoid all such movements, on account of the aforesaid corruption: but it is enough, for the conditions of a voluntary sin, that he be able to avoid each single one.
3. Man does not do perfectly himself what he does without the deliberation of reason, since the principal part of man does nothing therein: wherefore such is not perfectly a human act; and consequently it cannot be a perfect act of virtue or of sin, but is something imperfect of that kind. Therefore such movement of the sensuality as forestalls the reason, is a venial sin, which is something imperfect in the genus of sin.
Objection: 1. It would seem that mortal sin can be in the sensuality. Because an act is discerned by its object. Now it is possible to commit a mortal sin about the objects of the sensuality, e.g. about carnal pleasures. Therefore the act of the sensuality can be a mortal sin, so that mortal sin can be found in the sensuality.
2. Further, mortal sin is opposed to virtue. But virtue can be in the sensuality; for temperance and fortitude are virtues of the irrational parts, as the Philosopher states (Ethic. iii, 10). Therefore, since it is natural to contraries to be about the same subject, sensuality can be the subject of mortal sin.
3. Further, venial sin is a disposition to mortal sin. Now disposition and habit are in the same subject. Since therefore venial sin may be in the sensuality, as stated above (Article , ad 3), mortal sin can be there also.
On the contrary Augustine says (Retract. i, 23): "The inordinate movement of concupiscence, which is the sin of the sensuality, can even be in those who are in a state of grace," in whom, however, mortal sin is not to be found. Therefore the inordinate movement of the sensuality is not a mortal sin.
I answer that Just as a disorder which destroys the principle of the body's life causes the body's death, so too a disorder which destroys the principle of spiritual life, viz. the last end, causes spiritual death, which is mortal sin, as stated above (Question , Article ). Now it belongs to the reason alone, and not to the sensuality, to order anything to the end: and disorder in respect of the end can only belong to the power whose function it is to order others to the end. Wherefore mortal sin cannot be in the sensuality, but only in the reason.
Reply to Objection: 1. The act of the sensuality can concur towards a mortal sin: yet the fact of its being a mortal sin is due, not to its being an act of the sensuality, but to its being an act of reason, to whom the ordering to the end belongs. Consequently mortal sin is imputed, not to the sensuality, but to reason.
2. An act of virtue is perfected not only in that it is an act of the sensuality, but still more in the fact of its being an act of reason and will, whose function it is to choose: for the act of moral virtue is not without the exercise of choice: wherefore the act of moral virtue, which perfects the appetitive power, is always accompanied by an act of prudence, which perfects the rational power; and the same applies to mortal sin, as stated (ad 1).
3. A disposition may be related in three ways to that to which it disposes: for sometimes it is the same thing and is in the same subject; thus inchoate science is a disposition to perfect science: sometimes it is in the same subject, but is not the same thing; thus heat is a disposition to the form of fire: sometimes it is neither the same thing, nor in the same subject, as in those things which are subordinate to one another in such a way that we can arrive at one through the other, e.g. goodness of the imagination is a disposition to science which is in the intellect. In this way the venial sin that is in the sensuality, may be a disposition to mortal sin, which is in the reason.
Objection: 1. It would seem that sin cannot be in the reason. For the sin of any power is a defect thereof. But the fault of the reason is not a sin, on the contrary, it excuses sin: for a man is excused from sin on account of ignorance. Therefore sin cannot be in the reason.
2. Further, the primary object of sin is the will, as stated above (Article ). Now reason precedes the will, since it directs it. Therefore sin cannot be in the reason.
3. Further, there can be no sin except about things which are under our control. Now perfection and defect of reason are not among those things which are under our control: since by nature some are mentally deficient, and some shrewd-minded. Therefore no sin is in the reason.
On the contrary Augustine says (De Trin. xii, 12) that sin is in the lower and in the higher reason.
I answer that The sin of any power is an act of that power, as we have clearly shown (Articles ,2,3). Now reason has a twofold act: one is its proper act in respect of its proper object, and this is the act of knowing the truth; the other is the act of reason as directing the other powers. Now in both of these ways there may be sin in the reason. First, in so far as it errs in the knowledge of truth, which error is imputed to the reason as a sin, when it is in ignorance or error about what it is able and ought to know: secondly, when it either commands the inordinate movements of the lower powers, or deliberately fails to check them.
Reply to Objection: 1. This argument considers the defect in the proper act of the reason in respect of its proper object, and with regard to the case when it is a defect of knowledge about something which one is unable to know: for then this defect of reason is not a sin, and excuses from sin, as is evident with regard to the actions of madmen. If, however, the defect of reason be about something which a man is able and ought to know, he is not altogether excused from sin, and the defect is imputed to him as a sin. The defect which belongs only to the act of directing the other powers, is always imputed to reason as a sin, because it can always obviate this defect by means of its proper act.
2. As stated above (Question , Article ), when we were treating of the acts of the will and reason, the will moves and precedes the reason, in one way, and the reason moves and precedes the will in another: so that both the movement of the will can be called rational, and the act of the reason, voluntary. Accordingly sin is found in the reason, either through being a voluntary defect of the reason, or through the reason being the principle of the will's act.
3. The Reply to the Third Objection is evident from what has been said (ad 1).
Objection: 1. It would seem that the sin of morose delectation is not in the reason. For delectation denotes a movement of the appetitive power, as stated above (Question , Article ). But the appetitive power is distinct from the reason, which is an apprehensive power. Therefore morose delectation is not in the reason.
2. Further, the object shows to which power an act belongs, since it is through the act that the power is directed to its object. Now a morose delectation is sometimes about sensible goods, and not about the goods of the reason. Therefore the sin of morose delectation is not in the reason.
3. Further, a thing is said to be morose [*From the Latin 'mora'---delay] through taking a length of time. But length of time is no reason why an act should belong to a particular power. Therefore morose delectation does not belong to the reason.
On the contrary Augustine says (De Trin. xii, 12) that "if the consent to a sensual delectation goes no further than the mere thought of the pleasure, I deem this to be like as though the woman alone had partaken of the forbidden fruit." Now "the woman" denotes the lower reason, as he himself explains (De Trin. xii, 12). Therefore the sin of morose delectation is in the reason.
I answer that As stated (Article ), sin may be in the reason, not only in respect of reason's proper act, but sometimes in respect of its directing human actions. Now it is evident that reason directs not only external acts, but also internal passions. Consequently when the reason fails in directing the internal passions, sin is said to be in the reason, as also when it fails in directing external actions. Now it fails, in two ways, in directing internal passions: first, when it commands unlawful passions; for instance, when a man deliberately provokes himself to a movement of anger, or of lust: secondly, when it fails to check the unlawful movement of a passion; for instance, when a man, having deliberately considered that a rising movement of passion is inordinate, continues, notwithstanding, to dwell [immoratur] upon it, and fails to drive it away. And in this sense the sin of morose delectation is said to be in the reason.
Reply to Objection: 1. Delectation is indeed in the appetitive power as its proximate principle; but it is in the reason as its first mover, in accordance with what has been stated above (Article ), viz. that actions which do not pass into external matter are subjected in their principles.
2. Reason has its proper elicited act about its proper object; but it exercises the direction of all the objects of those lower powers that can be directed by the reason: and accordingly delectation about sensible objects comes also under the direction of reason.
3. Delectation is said to be morose not from a delay of time, but because the reason in deliberating dwells [immoratur] thereon, and fails to drive it away, "deliberately holding and turning over what should have been cast aside as soon as it touched the mind," as Augustine says (De Trin. xii, 12).
Objection: 1. It would seem that the sin of consent to the act is not in the higher reason. For consent is an act of the appetitive power, as stated above (Question , Article ): whereas the reason is an apprehensive power. Therefore the sin of consent to the act is not in the higher reason.
2. Further, "the higher reason is intent on contemplating and consulting the eternal law," as Augustine states (De Trin. xii, 7). [*'Rationes aeternae,' cf. I 15,2 I 15,3] where as in similar passages 'ratio' has been rendered by the English 'type,' because St. Thomas was speaking of the Divine 'idea' as the archetype of the creature. Hence the type or idea is a rule of conduct, and is identified with the eternal law, (cf. Article , Objection ; Article )]. But sometimes consent is given to an act, without consulting the eternal law: since man does not always think about Divine things, whenever he consents to an act. Therefore the sin of consent to the act is not always in the higher reason.
3. Further, just as man can regulate his external actions according to the eternal law, so can he regulate his internal pleasures or other passions. But "consent to a pleasure without deciding to fulfil it by deed, belongs to the lower reason," as Augustine states (De Trin. xii, 2). Therefore the consent to a sinful act should also be sometimes ascribed to the lower reason.
4. Further, just as the higher reason excels the lower, so does the reason excel the imagination. Now sometimes man proceeds to act through the apprehension of the power of imagination, without any deliberation of his reason, as when, without premeditation, he moves his hand, or foot. Therefore sometimes also the lower reason may consent to a sinful act, independently of the higher reason.
On the contrary Augustine says (De Trin. xii, 12): "If the consent to the evil use of things that can be perceived by the bodily senses, so far approves of any sin, as to point, if possible, to its consummation by deed, we are to understand that the woman has offered the forbidden fruit to her husband."
I answer that Consent implies a judgment about the thing to which consent is given. For just as the speculative reason judges and delivers its sentence about intelligible matters, so the practical reason judges and pronounces sentence on matters of action. Now we must observe that in every case brought up for judgment, the final sentence belongs to the supreme court, even as we see that in speculative matters the final sentence touching any proposition is delivered by referring it to the first principles; since, so long as there remains a yet higher principle, the question can yet be submitted to it: wherefore the judgment is still in suspense, the final sentence not being as yet pronounced. But it is evident that human acts can be regulated by the rule of human reason, which rule is derived from the created things that man knows naturally; and further still, from the rule of the Divine law, as stated above (Question , Article ). Consequently, since the rule of the Divine law is the higher rule, it follows that the ultimate sentence, whereby the judgment is finally pronounced, belongs to the higher reason which is intent on the eternal types. Now when judgment has to be pronounced on several points, the final judgment deals with that which comes last; and, in human acts, the action itself comes last, and the delectation which is the inducement to the action is a preamble thereto. Therefore the consent to an action belongs properly to the higher reason, while the preliminary judgment which is about the delectation belongs to the lower reason, which delivers judgment in a lower court: although the higher reason can also judge of the delectation, since whatever is subject to the judgment of the lower court, is subject also to the judgment of the higher court, but not conversely.
Reply to Objection: 1. Consent is an act of the appetitive power, not absolutely, but in consequence of an act of reason deliberating and judging, as stated above (Question , Article ). Because the fact that the consent is finally given to a thing is due to the fact that the will tends to that upon which the reason has already passed its judgment. Hence consent may be ascribed both to the will and to the reason.
2. The higher reason is said to consent, from the very fact that it fails to direct the human act according to the Divine law, whether or not it advert to the eternal law. For if it thinks of God's law, it holds it in actual contempt: and if not, it neglects it by a kind of omission. Therefore the consent to a sinful act always proceeds from the higher reason: because, as Augustine says (De Trin. xii, 12), "the mind cannot effectively decide on the commission of a sin, unless by its consent, whereby it wields its sovereign power of moving the members to action, or of restraining them from action, it become the servant or slave of the evil deed."
3. The higher reason, by considering the eternal law, can direct or restrain the internal delectation, even as it can direct or restrain the external action: nevertheless, before the judgment of the higher reason is pronounced the lower reason, while deliberating the matter in reference to temporal principles, sometimes approves of this delectation: and then the consent to the delectation belongs to the lower reason. If, however, after considering the eternal law, man persists in giving the same consent, such consent will then belong to the higher reason.
4. The apprehension of the power of imagination is sudden and indeliberate: wherefore it can cause an act before the higher or lower reason has time to deliberate. But the judgment of the lower reason is deliberate, and so requires time, during which the higher reason can also deliberate; consequently, if by its deliberation it does not check the sinful act, this will deservedly by imputed to it.
Objection: 1. It would seem that consent to delectation is not a mortal sin, for consent to delectation belongs to the lower reason, which does not consider the eternal types, i.e. the eternal law, and consequently does not turn away from them. Now every mortal sin consists in turning away from Augustine's definition of mortal sin, which was quoted above (Question , Article ). Therefore consent to delectation is not a mortal sin.
2. Further, consent to a thing is not evil, unless the thing to which consent is given be evil. Now "the cause of anything being such is yet more so," or at any rate not less. Consequently the thing to which a man consents cannot be a lesser evil than his consent. But delectation without deed is not a mortal sin, but only a venial sin. Therefore neither is the consent to the delectation a mortal sin.
3. Further, delectations differ in goodness and malice, according to the difference of the deeds, as the Philosopher states (Ethic. x, 3,5). Now the inward thought is one thing, and the outward deed, e.g. fornication, is another. Therefore the delectation consequent to the act of inward thought, differs in goodness and malice from the pleasure of fornication, as much as the inward thought differs from the outward deed; and consequently there is a like difference of consent on either hand. But the inward thought is not a mortal sin, nor is the consent to that thought: and therefore neither is the consent to the delectation.
4. Further, the external act of fornication or adultery is a mortal sin, not by reason of the delectation, since this is found also in the marriage act, but by reason of an inordinateness in the act itself. Now he that consents to the delectation does not, for this reason, consent to the inordinateness of the act. Therefore he seems not to sin mortally.
5. Further, the sin of murder is more grievous than simple fornication. Now it is not a mortal sin to consent to the delectation resulting from the thought of murder. Much less therefore is it a mortal sin to consent to the delectation resulting from the thought of fornication.
6. Further, the Lord's prayer is recited every day for the remission of venial sins, as Augustine asserts (Enchiridion lxxviii). Now Augustine teaches that consent to delectation may be driven away by means of the Lord's Prayer: for he says (De Trin. xii, 12) that "this sin is much less grievous than if it be decided to fulfil it by deed: wherefore we ought to ask pardon for such thoughts also, and we should strike our breasts and say: 'Forgive us our trespasses.'" Therefore consent to delectation is a venial sin.
On the contrary Augustine adds after a few words: "Man will be altogether lost unless, through the grace of the Mediator, he be forgiven those things which are deemed mere sins of thought, since without the will to do them, he desires nevertheless to enjoy them." But no man is lost except through mortal sin. Therefore consent to delectation is a mortal sin.
I answer that There have been various opinions on this point, for some have held that consent to delectation is not a mortal sin, but only a venial sin, while others have held it to be a mortal sin, and this opinion is more common and more probable. For we must take note that since every delectation results from some action, as stated in Ethic. x, 4, and again, that since every delectation may be compared to two things, viz. to the operation from which it results, and to the object in which a person takes delight. Now it happens that an action, just as a thing, is an object of delectation, because the action itself can be considered as a good and an end, in which the person who delights in it, rests. Sometimes the action itself, which results in delectation, is the object of delectation, in so far as the appetitive power, to which it belongs to take delight in anything, is brought to bear on the action itself as a good: for instance, when a man thinks and delights in his thought, in so far as his thought pleases him; while at other times the delight consequent to an action, e.g. a thought, has for its object another action, as being the object of his thought; and then his thought proceeds from the inclination of the appetite, not indeed to the thought, but to the action thought of. Accordingly a man who is thinking of fornication, may delight in either of two things: first, in the thought itself, secondly, in the fornication thought of. Now the delectation in the thought itself results from the inclination of the appetite to the thought; and the thought itself is not in itself a mortal sin; sometimes indeed it is only a venial sin, as when a man thinks of such a thing for no purpose; and sometimes it is no sin at all, as when a man has a purpose in thinking of it; for instance, he may wish to preach or dispute about it. Consequently such affection or delectation in respect of the thought of fornication is not a mortal sin in virtue of its genus, but is sometimes a venial sin and sometimes no sin at all: wherefore neither is it a mortal sin to consent to such a thought. In this sense the first opinion is true.But that a man in thinking of fornication takes pleasure in the act thought of, is due to his desire being inclined to this act. Wherefore the fact that a man consents to such a delectation, amounts to nothing less than a consent to the inclination of his appetite to fornication: for no man takes pleasure except in that which is in conformity with his appetite. Now it is a mortal sin, if a man deliberately chooses that his appetite be conformed to what is in itself a mortal sin. Wherefore such a consent to delectation in a mortal sin, is itself a mortal sin, as the second opinion maintains.
Reply to Objection: 1. Consent to delectation may be not only in the lower reason, but also in the higher reason, as stated above (Article ). Nevertheless the lower reason may turn away from the eternal types, for, though it is not intent on them, as regulating according to them, which is proper to the higher reason, yet, it is intent on them, as being regulated according to them: and by turning from them in this sense, it may sin mortally; since even the acts of the lower powers and of the external members may be mortal sins, in so far as the direction of the higher reason fails in directing them according to the eternal types.
2. Consent to a sin that is venial in its genus, is itself a venial sin, and accordingly one may conclude that the consent to take pleasure in a useless thought about fornication, is a venial sin. But delectation in the act itself of fornication is, in its genus, a mortal sin: and that it be a venial sin before the consent is given, is accidental, viz. on account of the incompleteness of the act: which incompleteness ceases when the deliberate consent has been given, so that therefore it has its complete nature and is a mortal sin.
3. This argument considers the delectation which has the thought for its object.
4. The delectation which has an external act for its object, cannot be without complacency in the external act as such, even though there be no decision to fulfil it, on account of the prohibition of some higher authority: wherefore the act is inordinate, and consequently the delectation will be inordinate also.
5. The consent to delectation, resulting from complacency in an act of murder thought of, is a mortal sin also: but not the consent to delectation resulting from complacency in the thought of murder.
6. The Lord's Prayer is to be said in order that we may be preserved not only from venial sin, but also from mortal sin.
Objection: 1. It would seem that there cannot be venial sin in the higher reason as directing the lower powers, i.e. as consenting to a sinful act. For Augustine says (De Trin. xii, 7) that the "higher reason is intent on considering and consulting the eternal law." But mortal sin consists in turning away from the eternal law. Therefore it seems that there can be no other than mortal sin in the higher reason.
2. Further, the higher reason is the principle of the spiritual life, as the heart is of the body's life. But the diseases of the heart are deadly. Therefore the sins of the higher reason are mortal.
3. Further, a venial sin becomes a mortal sin if it be done out of contempt. But it would seem impossible to commit even a venial sin, deliberately, without contempt. Since then the consent of the higher reason is always accompanied by deliberate consideration of the eternal law, it seems that it cannot be without mortal sin, on account of the contempt of the Divine law.
On the contrary Consent to a sinful act belongs to the higher reason, as stated above (Article ). But consent to an act of venial sin is itself a venial sin. Therefore a venial sin can be in the higher reason.
I answer that As Augustine says (De Trin. xii, 7), the higher reason "is intent on contemplating or consulting the eternal law"; it contemplates it by considering its truth; it consults it by judging and directing other things according to it: and to this pertains the fact that by deliberating through the eternal types, it consents to an act or dissents from it. Now it may happen that the inordinateness of the act to which it consents, is not contrary to the eternal law, in the same way as mortal sin is, because it does not imply aversion from the last end, but is beside that law, as an act of venial sin is. Therefore when the higher reason consents to the act of a venial sin, it does not turn away from the eternal law: wherefore it sins, not mortally, but venially.
Reply to Objection: 1. This suffices for the Reply to the First Objection.
2. Disease of the heart is twofold: one which is in the very substance of the heart, and affects its natural consistency, and such a disease is always mortal: the other is a disease of the heart consisting in some disorder either of the movement or of the parts surrounding the heart, and such a disease is not always mortal. In like manner there is mortal sin in the higher reason whenever the order itself of the higher reason to its proper object which is the eternal law, is destroyed; but when the disorder leaves this untouched, the sin is not mortal but venial.
3. Deliberate consent to a sin does not always amount to contempt of the Divine law, but only when the sin is contrary to the Divine law.
Objection: 1. It would seem that venial sin cannot be in the higher reason as such, i.e. as considering the eternal law. For the act of a power is not found to fail except that power be inordinately disposed with regard to its object. Now the object of the higher reason is the eternal law, in respect of which there can be no disorder without mortal sin. Therefore there can be no venial sin in the higher reason as such.
2. Further, since the reason is a deliberative power, there can be no act of reason without deliberation. Now every inordinate movement in things concerning God, if it be deliberate, is a mortal sin. Therefore venial sin is never in the higher reason as such.
3. Further, it happens sometimes that a sin which takes us unawares, is a venial sin. Now a deliberate sin is a mortal sin, through the reason, in deliberating, having recourse to some higher good, by acting against which, man sins more grievously; just as when the reason in deliberating about an inordinate pleasurable act, considers that it is contrary to the law of God, it sins more grievously in consenting, than if it only considered that it is contrary to moral virtue. But the higher reason cannot have recourse to any higher tribunal than its own object. Therefore if a movement that takes us unawares is not a mortal sin, neither will the subsequent deliberation make it a mortal sin; which is clearly false. Therefore there can be no venial sin in the higher reason as such.
On the contrary A sudden movement of unbelief is a venial sin. But it belongs to the higher reason as such. Therefore there can be a venial sin in the higher reason as such.
I answer that The higher reason regards its own object otherwise than the objects of the lower powers that are directed by the higher reason. For it does not regard the objects of the lower powers, except in so far as it consults the eternal law about them, and so it does not regard them save by way of deliberation. Now deliberate consent to what is a mortal sin in its genus, is itself a mortal sin; and consequently the higher reason always sins mortally, if the acts of the lower powers to which it consents are mortal sins.With regard to its own object it has a twofold act, viz. simple "intuition," and "deliberation," in respect of which it again consults the eternal law about its own object. But in respect of simple intuition, it can have an inordinate movement about Divine things, as when a man suffers a sudden movement of unbelief. And although unbelief, in its genus, is a mortal sin, yet a sudden movement of unbelief is a venial sin, because there is no mortal sin unless it be contrary to the law of God. Now it is possible for one of the articles of faith to present itself to the reason suddenly under some other aspect, before the eternal law, i.e. the law of God, is consulted, or can be consulted, on the matter; as, for instance, when a man suddenly apprehends the resurrection of the dead as impossible naturally, and rejects it, as soon as he had thus apprehended it, before he has had time to deliberate and consider that this is proposed to our belief in accordance with the Divine law. If, however, the movement of unbelief remains after this deliberation, it is a mortal sin. Therefore, in sudden movements, the higher reason may sin venially in respect of its proper object, even if it be a mortal sin in its genus; or it may sin mortally in giving a deliberate consent; but in things pertaining to the lower powers, it always sins mortally, in things which are mortal sins in their genus, but not in those which are venial sins in their genus.
Reply to Objection: 1. A sin which is against the eternal law, though it be mortal in its genus, may nevertheless be venial, on account of the incompleteness of a sudden action, as stated.
2. In matters of action, the simple intuition of the principles from which deliberation proceeds, belongs to the reason, as well as the act of deliberation: even as in speculative matters it belongs to the reason both to syllogize and to form propositions: consequently the reason also can have a sudden movement.
3. One and the same thing may be the subject of different considerations, of which one is higher than the other; thus the existence of God may be considered, either as possible to be known by the human reason, or as delivered to us by Divine revelation, which is a higher consideration. And therefore, although the object of the higher reason is, in its nature, something sublime, yet it is reducible to some yet higher consideration: and in this way, that which in the sudden movement was not a mortal sin, becomes a mortal sin in virtue of the deliberation which brought it into the light of a higher consideration, as was explained above.
Summa Th. I-II EN Qu.74 a.2