Summa Theologiae Moralis, vol. I: De Principiis

S. Th. I-II, q. 64, a. 1, 2, 3 ; De Virt. q. 1, a. 13.

600. Adage : « Moral virtue is in a mean » :

1. It is not to be understood of a mean according to essence and the notion of habit, as if it signified that virtue is essentially between two extreme vices, one of which is opposed to it by excess, the other by defect : for this is false of the virtue of justice, to which only injustice is opposed. For the rest, by the same sin one sins at once by excess and by defect, for he who gives to one less than he owes, gives to another or to himself more than he can ; and if anyone gives to another more than he owes, he is no longer just but liberal.

2. But it is to be understood causally, of a mean according to effect and the notion of object, and it signifies that virtue has for its object a mean between excess (more) and defect (less) in its proper matter : for it makes our appetite choose operations or passions neither more nor less, but precisely in the measure which right reason dictates : thus for temperance, excess in the matter consists in using pleasures more than is fitting, defect in not using them when one should ; the mean, which is the object of temperance, is to use pleasures, as, when, in the manner,... one ought.

It is proved : The good of moral virtue is in adequation or conformity to the rule, i.e. to right reason, without departing from it. But adequation is a mean between excess, by which something exceeds the measure, and defect, by which it falls short of it or does not attain it. Therefore the good of moral virtue is in a mean.

But if virtue is called the ultimate of a potency, which indicates a summit, not a mean ; — this is to be understood according to the perfection of the act, for thus virtue is at the summit of perfection ; not however according to the quantity of the matter, for thus virtue is in a mean.

3. But the sense is not of a mean by reason of the subject and according to the sole measure of our weak condition, namely that virtue is to be exercised moderately so that man cannot tend toward any maximum ; — for the maximum is sometimes conformed to reason, as is clear of fortitude, magnanimity, virginity, etc., and yet in this case virtue is still in a mean, because excess is to tend toward that maximum when one ought not.

601. The mean of virtue is the mean of reason, because it is conformity to the measure of right reason, which measure it does not exceed and from which it does not depart : between excess and defect, adequation to the measure holds the mean. Hence it is defined : the property of virtue whereby it so moves about its matter as to beware of excess and defect. Reason constitutes, dictates, and imposes that mean upon the moral virtues through prudence ; whence S. Thomas says that « that mean belongs to prudence as regulating and measuring, to moral virtue as measured and regulated » (a. 3) ; therefore prudence is in the mean because it itself is the measure of moral virtue.

602. The mean of reason is sometimes the mean of the thing, namely in justice, inasmuch as reason dictates to justice that it pay what is due to equality, or give a thing equal to the person of another or to the thing (whether arithmetically or proportionally), neither more nor less.

For reason determines the mean of virtue in its proper matter. But justice is about operations which consist in external things without regard to the diverse conditions of the agent. Therefore the mean of justice consists in a thing determined according to itself, without regard to the agent, inasmuch as it gives to each one what is due, neither more nor less. And thus the mean of reason is the mean of the thing.

But in the other moral virtues, which are about interior passions, the mean of reason is taken by comparison to us, whence it varies according to persons, qualities, circumstances, and diverse attitudes toward passions. Thus excess in drinking for one is not for another.

603. Observations. — 1°) Even the intellectual virtues are in the mean of the thing. The good of the intellect is the true, which depends on things which are the measure of our intellect. « Thus therefore the good of an intellectual virtue consists in a certain mean by conformity to the thing itself, according as it says that a thing is what it is or is not what it is not ; in which the notion of the true consists. Excess is taken according to a false affirmation by which what is not is said to be ; defect however is taken according to a false negation by which what is is said not to be » (a. 3).

2°) Moreover the practical intellectual virtues have the character of a rule with regard to our works, and so they are in the mean of reason just as the rule itself which imposes a mean. Thus prudence imposes a mean on the acts and moral virtues, and art on artifacts.

3°) Certain theologians say that the virtues of Religion and Penitence are not in a mean, but this is false : for although under one respect excess cannot be given in their matter, inasmuch as the worship rendered to God and satisfaction for sins cannot be excessive in quantity, under other respects however : quality, manner, time, etc. in their matter excess is given.