I answer that, In whatever things good consists in a due measure, evil must of necessity ensue through excess or deficiency of that measure. Now in all things that are for an end, the good consists in a certain measure: since whatever is directed to an end must needs be commensurate with the end, as, for instance, medicine is commensurate with health, as the Philosopher observes (Polit. i, 6). External goods come under the head of things useful for an end, as stated above (Q. 117, A. 3; I-II, Q. 2, A. 1). Hence it must needs be that man's good in their respect consists in a certain measure, in other words, that man seeks, according to a certain measure, to have external riches, in so far as they are necessary for him to live in keeping with his condition of life. Wherefore it will be a sin for him to exceed this measure, by wishing to acquire or keep them immoderately. This is what is meant by covetousness, which is defined as "immoderate love of possessing." It is therefore evident that covetousness is a sin.
Reply Obj. 1: It is natural to man to desire external things as means to an end: wherefore this desire is devoid of sin, in so far as it is held in check by the rule taken from the nature of the end. But covetousness exceeds this rule, and therefore is a sin.
Reply Obj. 2: Covetousness may signify immoderation about external things in two ways. First, so as to regard immediately the acquisition and keeping of such things, when, to wit, a man acquires or keeps them more than is due. In this way it is a sin directly against one's neighbor, since one man cannot over-abound in external riches, without another man lacking them, for temporal goods cannot be possessed by many at the same time. Secondly, it may signify immoderation in the internal affection which a man has for riches when, for instance, a man loves them, desires them, or delights in them, immoderately. In this way by covetousness a man sins against himself, because it causes disorder in his affections, though not in his body as do the sins of the flesh.
As a consequence, however, it is a sin against God, just as all mortal sins, inasmuch as man contemns things eternal for the sake of temporal things.
Reply Obj. 3: Natural inclinations should be regulated according to reason, which is the governing power in human nature. Hence though old people seek more greedily the aid of external things, just as everyone that is in need seeks to have his need supplied, they are not excused from sin if they exceed this due measure of reason with regard to riches. _______________________
SECOND ARTICLE [II-II, Q. 118, Art. 2]
Whether Covetousness Is a Special Sin?
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 stated above (I-II, Q. 71, A. 6, Obj. 3). Therefore covetousness is a general sin.
Obj. 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 (Q. 117, A. 2, ad 2). Therefore covetousness is a desire for any external thing: and consequently seems to be a general sin.
Obj. 3: Further, a gloss on Rom. 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 (Ex. 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.