Objection 1: It would seem that backbiting is the gravest of all sins committed against one's neighbor. Because a gloss on Ps.108:4, |Instead of making me a return of love they detracted me,| a gloss says: |Those who detract Christ in His members and slay the souls of future believers are more guilty than those who killed the flesh that was soon to rise again.| From this it seems to follow that backbiting is by so much a graver sin than murder, as it is a graver matter to kill the soul than to kill the body. Now murder is the gravest of the other sins that are committed against one's neighbor. Therefore backbiting is absolutely the gravest of all.
Objection 2: Further, backbiting is apparently a graver sin than reviling, because a man can withstand reviling, but not a secret backbiting. Now backbiting is seemingly a graver sin than adultery, because adultery unites two persons in one flesh, whereas reviling severs utterly those who were united. Therefore backbiting is more grievous than adultery: and yet of all other sins a man commits against his neighbor, adultery is most grave.
Objection 3: Further, reviling arises from anger, while backbiting arises from envy, according to Gregory (Moral. xxxi, 45). But envy is a graver sin than anger. Therefore backbiting is a graver sin than reviling; and so the same conclusion follows as before.
Objection 4: Further, the gravity of a sin is measured by the gravity of the defect that it causes. Now backbiting causes a most grievous defect, viz. blindness of mind. For Gregory says (Regist. xi, Ep.2): |What else do backbiters but blow on the dust and stir up the dirt into their eyes, so that the more they breathe of detraction, the less they see of the truth?| Therefore backbiting is the most grievous sin committed against one's neighbor.
On the contrary, It is more grievous to sin by deed than by word. But backbiting is a sin of word, while adultery, murder, and theft are sins of deed. Therefore backbiting is not graver than the other sins committed against one's neighbor.
I answer that, The essential gravity of sins committed against one's neighbor must be weighed by the injury they inflict on him, since it is thence that they derive their sinful nature. Now the greater the good taken away, the greater the injury. And while man's good is threefold, namely the good of his soul, the good of his body, and the good of external things; the good of the soul, which is the greatest of all, cannot be taken from him by another save as an occasional cause, for instance by an evil persuasion, which does not induce necessity. On the other hand the two latter goods, viz. of the body and of external things, can be taken away by violence. Since, however, the goods of the body excel the goods of external things, those sins which injure a man's body are more grievous than those which injure his external things. Consequently, among other sins committed against one's neighbor, murder is the most grievous, since it deprives man of the life which he already possesses: after this comes adultery, which is contrary to the right order of human generation, whereby man enters upon life. In the last place come external goods, among which a man's good name takes precedence of wealth because it is more akin to spiritual goods, wherefore it is written (Prov.22:1): |A good name is better than great riches.| Therefore backbiting according to its genus is a more grievous sin than theft, but is less grievous than murder or adultery. Nevertheless the order may differ by reason of aggravating or extenuating circumstances.
The accidental gravity of a sin is to be considered in relation to the sinner, who sins more grievously, if he sins deliberately than if he sins through weakness or carelessness. In this respect sins of word have a certain levity, in so far as they are apt to occur through a slip of the tongue, and without much forethought.
Reply to Objection 1: Those who detract Christ by hindering the faith of His members, disparage His Godhead, which is the foundation of our faith. Wherefore this is not simple backbiting but blasphemy.
Reply to Objection 2: Reviling is a more grievous sin than backbiting, in as much as it implies greater contempt of one's neighbor: even as robbery is a graver sin than theft, as stated above (Q, A). Yet reviling is not a more grievous sin than adultery. For the gravity of adultery is measured, not from its being a union of bodies, but from being a disorder in human generation. Moreover the reviler is not the sufficient cause of unfriendliness in another man, but is only the occasional cause of division among those who were united, in so far, to wit, as by declaring the evils of another, he for his own part severs that man from the friendship of other men, though they are not forced by his words to do so. Accordingly a backbiter is a murderer |occasionally,| since by his words he gives another man an occasion for hating or despising his neighbor. For this reason it is stated in the Epistle of Clement [*Ad Jacob. Ep. i], that |backbiters are murderers,| i.e. occasionally; because |he that hateth his brother is a murderer| (1 Jn.3:15).
Reply to Objection 3: Anger seeks openly to be avenged, as the Philosopher states (Rhet. ii, 2): wherefore backbiting which takes place in secret, is not the daughter of anger, as reviling is, but rather of envy, which strives by any means to lessen one's neighbor's glory. Nor does it follow from this that backbiting is more grievous than reviling: since a lesser vice can give rise to a greater sin, just as anger gives birth to murder and blasphemy. For the origin of a sin depends on its inclination to an end, i.e. on the thing to which the sin turns, whereas the gravity of a sin depends on what it turns away from.
Reply to Objection 4: Since |a man rejoiceth in the sentence of his mouth| (Prov.15:23), it follows that a backbiter more and more loves and believes what he says, and consequently more and more hates his neighbor, and thus his knowledge of the truth becomes less and less. This effect however may also result from other sins pertaining to hate of one's neighbor.