HKB
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.
Reply Obj. 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 be imputed to it.
EIGHTH ARTICLE [I-II, Q. 74, Art. 8]
Whether Consent to Delectation Is a Mortal Sin?
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 the Divine law, as is evident from Augustine's definition of mortal sin, which was quoted above (Q. 71, A. 6). Therefore consent to delectation is not a mortal sin.
Obj. 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.
Obj. 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.
Obj. 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.
Obj. 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.
Obj. 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.