Objection 1. It seems that covetousness is not a special sin. For Augustine says (De Lib. Arb. iii): "Covetousness, which in Greek is called philargyria, applies not only to silver or money, but also to anything that is desired immoderately." Now in every sin there is immoderate desire of something, because sin consists in turning away from the immutable good, and adhering to mutable goods, as state above (I-II, 71, 6, Objection 3). Therefore covetousness is a general sin.
Objection 2. Further, according to Isidore (Etym. x), "the covetous [avarus] man" is so called because he is "greedy for brass [avidus aeris]," i.e. money: wherefore in Greek covetousness is called philargyria, i.e. "love of silver." Now silver, which stands for money, signifies all external goods the value of which can be measured by money, as stated above (117, 2, ad 2). Therefore covetousness is a desire for any external thing: and consequently seems to be a general sin.
Objection 3. Further, a gloss on Romans 7:7, "For I had not known concupiscence," says: "The law is good, since by forbidding concupiscence, it forbids all evil." Now the law seems to forbid especially the concupiscence of covetousness: hence it is written (Exodus 20:17): "Thou shalt not covet thy neighbor's goods." Therefore the concupiscence of covetousness is all evil, and so covetousness is a general sin.
On the contrary, Covetousness is numbered together with other special sins (Romans 1:29), where it is written: "Being filled with all iniquity, malice, fornication, covetousness" [Douay: 'avarice'], etc.
I answer that, Sins take their species from their objects, as stated above (I-II, 72, 1). Now the object of a sin is the good towards which an inordinate appetite tends. Hence where there is a special aspect of good inordinately desired, there is a special kind of sin. Now the useful good differs in aspect from the delightful good. And riches, as such, come under the head of useful good, since they are desired under the aspect of being useful to man. Consequently covetousness is a special sin, forasmuch as it is an immoderate love of having possessions, which are comprised under the name of money, whence covetousness [avaritia] is denominated.
Since, however, the verb "to have," which seems to have been originally employed in connection with possessions whereof we are absolute masters, is applied to many other things (thus a man is said to have health, a wife, clothes, and so forth, as stated in De Praedicamentis), consequently the term "covetousness" has been amplified to denote all immoderate desire for having anything whatever. Thus Gregory says in a homily (xvi in Ev.) that "covetousness is a desire not only for money, but also for knowledge and high places, when prominence is immoderately sought after." On this way covetousness is not a special sin: and in this sense Augustine speaks of covetousness in the passage quoted in the First Objection. Wherefore this suffices for the Reply to the First Objection.
Reply to Objection 2. All those external things that are subject to the uses of human life are comprised under the term "money," inasmuch as they have the aspect of useful good. But there are certain external goods that can be obtained by money, such as pleasures, honors, and so forth, which are desirable under another aspect. Wherefore the desire for such things is not properly called covetousness, in so far as it is a special vice.
Reply to Objection 3. This gloss speaks of the inordinate concupiscence for anything whatever. For it is easy to understand that if it is forbidden to covet another's possessions it is also forbidden to covet those things that can be obtained by means of those possessions.
Source: Summa Theologica (New Advent)