Objection 1. It would seem that pride is not a special sin. For Augustine says (De Nat. et Grat. xxix) that "you will find no sin that is not labelled pride"; and Prosper says (De Vita Contempl. iii, 2) that "without pride no sin is, or was, or ever will be possible." Therefore pride is a general sin.
Objection 2. Further, a gloss on Job 33:17, "That He may withdraw man from wickedness [Vulgate: 'From the things that he is doing, and may deliver him from pride']," says that "a man prides himself when he transgresses His commandments by sin." Now according to Ambrose [De Parad. viii], "every sin is a transgression of the Divine law, and a disobedience of the heavenly commandments." Therefore every sin is pride.
Objection 3. Further, every special sin is opposed to a special virtue. But pride is opposed to all the virtues, for Gregory says (Moral. xxxiv, 23): "Pride is by no means content with the destruction of one virtue; it raises itself up against all the powers of the soul, and like an all-pervading and poisonous disease corrupts the whole body"; and Isidore says (Etym. [De Summo Bono ii, 38) that it is "the downfall of all virtues." Therefore pride is not a special sin.
Objection 4. Further, every special sin has a special matter. Now pride has a general matter, for Gregory says (Moral. xxxiv, 23) that "one man is proud of his gold, another of his eloquence: one is elated by mean and earthly things, another by sublime and heavenly virtues." Therefore pride is not a special but a general sin.
On the contrary, Augustine says (De Nat. et Grat. xxix): "If he look into the question carefully, he will find that, according to God's law, pride is a very different sin from other vices." Now the genus is not different from its species. Therefore pride is not a general but a special sin.
I answer that, The sin of pride may be considered in two ways. First with regard to its proper species, which it has under the aspect of its proper object. On this way pride is a special sin, because it has a special object: for it is inordinate desire of one's own excellence, as stated (1, ad 2). Secondly, it may be considered as having a certain influence towards other sins. On this way it has somewhat of a generic character, inasmuch as all sins may arise from pride, in two ways. First directly, through other sins being directed to the end of pride which is one's own excellence, to which may be directed anything that is inordinately desired. Secondly, indirectly and accidentally as it were, that is by removing an obstacle, since pride makes a man despise the Divine law which hinders him from sinning, according to Jeremiah 2:20, "Thou hast broken My yoke, thou hast burst My bands, and thou saidst: I will not serve."
It must, however, be observed that this generic character of pride admits of the possibility of all vices arising from pride sometimes, but it does not imply that all vices originate from pride always. For though one may break the commandments of the Law by any kind of sin, through contempt which pertains to pride, yet one does not always break the Divine commandments through contempt, but sometimes through ignorance. and sometimes through weakness: and for this reason Augustine says (De Nat. et Grat. xxix) that "many things are done amiss which are not done through pride."
Reply to Objection 1. These words are introduced by Augustine into his book De Nat. et Grat., not as being his own, but as those of someone with whom he is arguing. Hence he subsequently disproves the assertion, and shows that not all sins are committed through pride. We might, however, reply that these authorities must be understood as referring to the outward effect of pride, namely the breaking of the commandments, which applies to every sin, and not to the inward act of pride, namely contempt of the commandment. For sin is committed, not always through contempt, but sometimes through ignorance, sometimes through weakness, as stated above.
Reply to Objection 2. A man may sometimes commit a sin effectively, but not affectively; thus he who, in ignorance, slays his father, is a parricide effectively, but not affectively, since he did not intend it. Accordingly he who breaks God's commandment is said to pride himself against God, effectively always, but not always affectively.
Reply to Objection 3. A sin may destroy a virtue in two ways. On one way by direct contrariety to a virtue, and thus pride does not corrupt every virtue, but only humility; even as every special sin destroys the special virtue opposed to it, by acting counter thereto. On another way a sin destroys a virtue, by making ill use of that virtue: and thus pride destroys every virtue, in so far as it finds an occasion of pride in every virtue, just as in everything else pertaining to excellence. Hence it does not follow that it is a general sin.
Reply to Objection 4. Pride regards a special aspect in its object, which aspect may be found in various matters: for it is inordinate love of one's excellence, and excellence may be found in various things.
Source: Summa Theologica (New Advent)