(a) In the act of a greater sin there may be extenuating circumstances, or in the act of a lesser sin aggravating circumstances that change their respective order. Example: Detraction is from its nature worse than theft; but, if the detraction does only small harm and the theft great harm, the theft is worse on account of the circumstances.
(b) In the persons who commit the sins there may be circumstances that change the order of guilt, so that he who commits the greater sin is less guilty. Examples: By his careless handling of a revolver, Balbus unintentionally causes lasting injury to a bystander. Caius without malice aforethought, but enraged by an unexpected insult, strikes a blow that destroys the sight in one eye of his adversary. Titus, angry because he has been dismissed from his employment, revenges himself by defacing a precious work of art. The bodily injuries caused by the first two men are more harmful than the injury to property done by Titus; but they sinned, the one from ignorance and the other from passion, whereas Titus sinned from malice. Hence, while the sins of Balbus and Caius are objectively or materially greater, that of Titus is greater subjectively or formally (i.e., as to guilt).
230. The Subjects of Sin.—By the subjects of sin we understand the powers of the soul in which sin is found. These powers are sometimes called the material causes of sin, just as the objects to which the sins tend are called their formal causes.
231. Just as virtuous habits have their seats in the will (e.g., justice), in the reason (e.g., prudence), and in the sensitive appetites (e.g., fortitude and temperance), so also contrary habits of vice may be found in these same faculties. (a) From the sensitive appetites proceed impulses caused by sense apprehension or bodily states, which, when they are inordinate and voluntary, are sinful (e.g., lust, envy; see 129, on Second Motions). (b) From the reason proceed false judgments caused by vincible ignorance, wrong direction deliberately given to the passions, pleasurable dwelling on inordinate thoughts, etc. (c) From the will proceed consent given to sins of the other powers, desires to commit sin, joy over sin already committed, etc.
232. As was said above (89-93), the external acts of the members of the body have no morality of their own, since they are completely subject to the will. Consequently, there are only three classes of sins, if classification is made according to the faculties from which the sins proceed: (a) sins of sensuality, which were spoken of above when we treated of the passions (177 sqq.); (b) sins of thought; (c) sins of desire and reminiscent approval.
233. Pleasurable dwelling on inordinate thoughts occurs when one deliberately, even though it be only for a moment, turns over in his mind some sinful object, delighting in it as if it were actually present, but not desiring that it be actually done. Example; One who imagines his neighbor’s house burned down, and rejoices at the mental picture, though for interested reasons he does not wish any conflagration in the vicinity.
234. The sinful thoughts just described are not to be confused with thoughts in which the object of the delight is something else than a sinful picture represented in the mind.
Thoughts of this latter kind are: (a) those in which one takes delight in an external act of sin being committed, as when one destroys one’s neighbor’s property with great internal satisfaction; here the thought forms one sin with the outer act; (b) those in which one delights in the mental image, not as it represents something morally wrong, but as it contains some object of lawful delight. There is a distinction between bad thoughts and thoughts on things that are bad. Examples: A moralist may think with pleasure about theft, not because he approves of it, but because it is a subject he has to know. A person may read detective stories with great interest, not because crime appeals to him, but because the style of the author is good, the details of the plot exciting, the manner of the crime mysterious, etc. There is danger in thoughts of this kind, however, if one indulges in them from mere curiosity, or immoderately, or if sin itself may take an attraction through them.
235. The gravity and species of pleasurable dwelling on inordinate thoughts vary according to the thing thought on (see on Objects, etc., 70 sqq.). (a) If pleasure is taken only in the object represented, the sin has the moral character of that object. Example: He who delights at the thought of theft, is guilty of theft; and if he thinks of a great theft, he is guilty of mortal sin. (b) If pleasure is also taken in the circumstances imaged in the mind, the sin takes on the added malice contained in the circumstances. Example: He who delights over the thought of the robbery of a church, is guilty of mental theft and sacrilege.
236. The following are signs that delight taken in a thought about sinful things is about their sinfulness, and not about some other of their properties: (a) if one thinks about them without any lawful necessity (such as that of study), but through mere curiosity, or without any good reason; (b) if at the same time one loves to think on them frequently and lingeringly, or shown great satisfaction whenever they are mentioned. Example: One who thinks about injustices for pastime and admires them as great exploits, who idolizes criminals as heroes or martyrs.