of law laid down by Isidore in the aforementioned passage [Etymologies, Bk. V, chap. xxi and Decretum, Pt. I, dist. IV, can. ii], namely: law must be necessary, it must be useful, and it must serve the common welfare. Accordingly, we shall omit the discussion of those conditions in the present context, inasmuch as we have expounded them above.
Again, as to justice on the part of the [legislative] agent, or commutative justice, everything set forth in Chapter Eight30 is pertinent; and consequently, it is also sufficiently clear that a law enacted [by an agent] without jurisdiction is null.
16.31 Concerning the necessity of distributive justice for the validity of a law. Thus there remains to be proved only the assertion regarding the other and third part of justice, which relates to the form, that is, to distributive equity.
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As to this factor, it is manifestly essential to the justice of law; since, if a law is imposed upon certain subjects, and not upon others to whom its subject-matter is equally applicable, then it is unjust, unless the exception is the result of some reasonable cause; a point which we have demonstrated above.
Again, the imposition of equal burdens upon all persons, without regard to the strength or capacity of each, is also contrary to reason and to justice, as is self-evident. And as to the fact that such injustice suffices to nullify a law, this is expressly affirmed by St. Thomas [I.–II, qu. 96, art. 4], when he says: ‘[Precepts] of this sort are manifestations of violence, rather than laws, and therefore they are not binding in conscience.’ In my opinion, this statement should be interpreted as referring to cases in which the disproportion and inequality of a law are so great that the latter redounds to the common detriment, and results in a grave and unjust burdening of many members of the community.32 If it so happens, however, that a law is in itself useful, while some exceptional instance to which it applies involves injustice, the law would not on that account be entirely null, nor would it cease to bind the other subjects. For, strictly speaking, no positive injustice (as it were) is done these subjects in the imposition of such a burden upon them, since the burden would not in itself be wrongful and since there results simply a measure of disproportion as between certain individuals and the community as a whole, a disproportion which would seem insufficient to nullify the law. But if, by an exception in favour of certain persons, others are burdened to a degree that exceeds the bounds of equity, then, to the extent of that excess, the law will fail to bind; while it will nevertheless be able to bind in other ways wherein it is not unjust. An example of this sort may be noted in the case of the laws on taxes, to which we shall later devote some remarks.
This part of our argument, moreover, may be further clarified by an explanation of the third principal condition for law, as laid down by Isidore [Etymologies, Bk. V, chap. xxi]—namely, that law must be practicable33
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(possibilis)—as well as by an explanation of other points which he also mentions in that context, as follows: ‘[law must be] in harmony with nature and with the custom of the country, and suitable to the time and place.’ For all these latter factors evidently serve to define that practicability, as we shall [presently] explain.
17.34 The third assertion: it is inherent in the nature of law that it shall relate to a practicable object. My third assertion, then, is this: it is inherent in the nature of law that it shall be practicable. This assertion, interpreted in a general sense, is applicable to every law.
However, in order that it may be proved and expounded, we should note that the term possibilis admits of two distinct interpretations: first, as opposed, absolutely, to impossibilis; secondly, as opposed to what is difficult, oppressive, and burdensome.
Taken in the first sense, this property of practicability is35 a self-evident [requirement of law], whatever the evasive arguments heretics may employ. For that which does not fall within the realm of freedom does not fall within that of law; but what is absolutely impossible does not come within the realm of freedom, since the latter of its very nature demands power to choose either of two alternatives; and therefore, [what is impossible] cannot be the subject-matter of law. Similarly, in cases of transgression or omission which cannot be reckoned as involving guilt or calling for punishment, it is impossible for law to intervene. For it is a part of the intrinsic nature of law that it shall contain some intrinsic element of obligation; but the omission to perform impossible deeds cannot be accounted guilt (any more than the performance of what is absolutely necessary is accounted deserving of a reward); and therefore, laws cannot be concerned with matters of this sort.
18.36 The assertion laid down by the Council of Trent is confirmed. Moreover, in this [first and absolute] sense, at all events, the Council of Trent (Sixth Session, and Chap. xi, canon 18) laid down the same assertion with
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regard to divine laws, also.37 Bellarmine, too (De Iustificatione, Bk. IV, chap. xi), and Andreas de Vega (Tridentini Decreti de Justificatione Expositio et Defensio, Bk. XI, chap. ix), opposing the heretics38 of that time, furnish extensive proofs to the same effect, based upon the Scriptures, upon the writings of the Fathers, and upon reason. Consequently, it is clear, a fortiori, that it is still more necessary for human laws to be practicable [in the absolute sense], because they are derived from a lesser power and are a participation (so to speak) in the divine law, and because the arguments adduced with respect to divine law, apply a fortiori with respect to these [human precepts].
There is the further argument that Augustine (De Natura et Gratia, Chap. xcvi [Chap. lxix]) says, not merely that God does not command that which is impossible, but also that, ‘It is a matter of firmest belief that a just and good God cannot have commanded impossibilities’. How, then, shall man have been able to command impossibilities? In this connexion, there is a vast difference between God and man. For God can command certain things impossible to nature, being able to render them possible through grace, which He for His part does not withhold in so far as it is necessary to the observance of His commandments; and consequently, the commandments of God relate always to something which is possible [of achievement], since that which we are able to achieve through those who befriend us, we are in an absolute sense able to achieve, provided that this friendly assistance is surely to be had and ready to hand. Human beings, however, cannot supply the power necessary for the fulfilment of precepts, and therefore they must necessarily assume that this power exists either by the force of nature
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or through grace, according to the character of the precept in question. At this point, to be sure, difficulties might be raised as to the possibility of loving God, of overcoming concupiscence, and of obeying the commandments; but we shall take up these matters in the treatise On Grace.39
19.40 The words of Isidore [Etymologies, Bk. V, chap. xxi], when he requires of law that it shall be practicable, should, then, be interpreted in accordance with this last part of our discussion. For Isidore is speaking principally of human law, and therefore, in order to explain the kind of practicability [to which he refers], he adds the phrase, ‘in harmony with nature’; that is to say, regard being had for the frailty and the constitution of nature. This condition, God Himself, in His own way, observes. For He refrains from prescribing that virginity be preserved by all persons, since this would be impossible, according to nature. So, also, the canon law refrains from prescribing that communion be received on all feast days, because such a practice could not be worthily observed, in view of the conditions inherent in nature. The same argument applies to other instances. Under this head comes the contention (upheld by St. Thomas) that law should be adapted to the subjects, in accordance with their [varying] capacities, so that the same fasts are not imposed upon children as upon their elders.
Isidore makes a further addition [ibid.], in the words, ‘[in harmony] with the custom of the country’. For custom is a second nature; and therefore, that which is
