Summa Theologiae Moralis, vol. I: De Principiis

S. Th. I-II, q. 91, a. 2 and q. 94, a. 1.

245. Thesis. The participation of the eternal law in the rational creature is a true law. — For it is

1. an ordinance of reason : the rational creature participates in the law intellectually and rationally, and therefore the participation of the eternal law in it is properly called law because it is something of reason : a dictate constituted by reason ; in other creatures it is not participated in rationally, whence in them the proper inclination is not called law except by similarity ;

2. it is promulgated by God to the community : for although the promulgation takes place in individuals, by the impression of reason, it nevertheless takes place by reason not indeed as it is particular, but as it is common and the same in all, proceeding from the author of nature ; 3) it is made for moral honesty, not of one, but of all humanity¹.

246. The essence of natural law. — Natural law is not law insofar as it is in the legislator as regulating, and therefore it is not the eternal law itself, but it is law as it is in the subjects as in those regulated, and therefore it is a participation, manifestation, passive promulgation of the eternal law in us.

And indeed :

1. It is not the will of God, whether necessary or free² : for actions are not good or evil because they are prescribed or forbidden by a willing God, but they are prescribed or forbidden because they are intrinsically in themselves good or evil, and indeed the good which are required as necessary by the order cannot but be prescribed, and the evil cannot but be forbidden. Whence if by an impossibility God should not will natural law, it would nevertheless become known to us in the same way and oblige, because human nature would be constituted in the same way by the divine reason commanding, and it itself as well as our acts would be ordered to the ultimate end³. Law, namely, is essentially an ordinance of reason, not will.

2. Nor does the will or power of God seem necessarily to be attended to in order that natural law be known. For moral necessity or obligation is the absolute necessity of a means to an absolutely necessary end (Q. D. de Ver. 17, a. 3), so that the means is necessary not only under the condition if one wishes the end, but absolutely because also the end is absolutely necessary and altogether imposed on us. Whence for knowing the law or obligation it suffices that there be present the absolute necessity of the end which is altogether imposed, and that the necessary connection of the means to the end be known, and consequently the obligation to those means. Now by physical necessity the end is imposed on us by nature : the supreme good of rational nature and the supreme happiness, so that we cannot not will it ; and reason a) is able to know that some particular goods befitting rational nature pertain to that end (as a necessary condition of true perfection and ultimate happiness), but others do not, and b) is able to perceive in this way the necessary connection of certain acts, as means, with that end. Therefore the absolute moral necessity of the means and the obligation arising from nature, or natural law, can be known, abstracting from God, namely without attending to the will or authority of God⁴. — Which does not however exclude that remotely and ultimately natural law and obligation depend on God, and that, with God known, it is more fully and perfectly perceived.

3. It is nevertheless not a categorical imperative of autonomous reason or will (Kant and the Rationalists). For conciliar autonomy cannot be reconciled with the idea of true obligation, because human reason cannot oblige itself. Whence obligation is not constituted by human reason, but is imposed from the necessary inclination of our nature, which cannot be changed by us and which always persists immutable. — Moreover this opinion rests on the false foundation that man is to himself an end, or an end in himself (cf. Syll. prop. 3 and 50), whereas he is essentially the creature of God, depending on him and ordered to him. The ultimate end, namely, is not constituted by reason but by the author of nature.

Therefore, considered in the first act, natural law is the habitual inclination of rational nature to its proper acts, namely to knowing and desiring the end or perfect good, and the means necessarily conducing to it, or to choosing honest acts ; whence nature is truly to itself a law, in this sense that from the necessary and inescapable inclination of nature to the end arises the obligation to employing the means. In other words, natural law is the light of natural reason by which we are able to discern what is good to be done or evil to be avoided ; which light shows goodness and malice and is the rule of our acts, inasmuch as it is derived from the divine light and is the impression of the divine light in us. — Considered in the second act, law is the actual dictate or judgment of reason, prescribing in a general way what is good to be done, what evil to be avoided. Hence

a) although natural law is not a habit, since it is not that by which reason acts, but what it dictates, the precepts of natural law are nevertheless not always actually considered by reason, and then they are in it habitually, and so natural law can be called a habit, because it is held habitually ;

b) it differs from synderesis, which is not the innate light of reason or its actual dictate, but is a habit (or facility, not strictly innate but spontaneously flowing from the intellect) by which we easily enunciate not all but the first moral principles ; whence by virtue [of this habit] it contains these principles ;

c) it differs from conscience, which is not a general norm of acting but a judgment about things to be done in particular.

247. The foundation of natural law. — Not only about the essence, but also the foundation of the law or natural obligation, and consequently of every obligation, must be sought ; for positive obligation is founded upon the obligation of natural law, inasmuch as this prescribes obedience to superiors.

Now from what has been said it is clear :

1. The unique, sufficient, or ultimate foundation is not the will of God, whether free or necessary : not free because we are dealing with a necessary law, not necessary because it depends on something prior from which it has its necessity, namely on the wisdom and essence of God (Q. D. de Ver. 23, a. 6) ; and therefore it is not the ultimate, unique, and sufficient foundation. — The adversaries indeed say that no law is given without a legislator, no precept can be conceived without the will and authority of one prescribing. But

a) this is true of positive law, which is not necessary, not of natural law whose obligation arises from the nature of things and from the necessary tendency of our nature to the end ; —

b) moreover, by saying that natural law is obligatory because reason dictates that the will of God commanding is to be obeyed, they will hardly free themselves from contradiction, because the said principle, as prescribed by reason alone, is known as obligatory and does not ultimately depend on the knowledge of the will of God ; otherwise there would be a vicious circle ; —

c) finally the first principles of natural law, e.g. good is to be done, etc., are known before the knowledge of God, just as this precedes the very knowledge of the terms of which it consists and by which, being known, it is enunciated at once⁵. Whence although God in the ontological order is the necessary foundation of natural law, not so in the logical order of knowledge.

2. Nor is the foundation human reason alone, because just as the effect depends more on the first cause than on the second cause, so obligation depends more on the author of nature and the eternal law than on the nature and human reason participated from God : for the essential order of things is not from reason nor from itself but is derived from the eternal law.

The foundation seems to be distinguished as twofold :

a) One, secondary and proximate : human nature itself, completely considered with its essential and necessary relations, — or its ultimate end absolutely imposed on it, — or the essential order of things according to which some have a necessary connection with the ultimate end ; and this is sufficient for conceiving true and properly so-called natural obligation, as we have said.

b) The other, primary, remote, and ultimate : the very intellect of God, or the eternal law with its root, the divine essence. For the eternal law is the source of nature and of human reason, and this is not the rule of our acts except from the divine reason of which it is a participation. In the same way there is a twofold foundation of the principles of speculative reason and of eternal truths : namely, the proximate, the nature of things and the relations that obtain between them (which suffices for conceiving necessary truths), and the ultimate, which is the essence and intellect of God. And just as we are able to know the truth of the first principles of speculative reason from the proximate foundation alone, the nature of things, without knowing their ultimate foundation, the divine intellect ; so we are able to know the truth and obligation of the first principles of practical reason, without knowing their ultimate foundation : the divine intellect and the eternal law.

248. Corollary : The system of lay morality, or, as they say, of obligation independent of God⁶, is therefore to be refuted by saying that it is

a) essentially incomplete, since it is silent about God the true ultimate end and about our duties toward God ; b) false, inasmuch as it affirms that natural law is founded in nature or reason alone, to the exclusion of the eternal law of God ;

c) inefficacious, because the law lacks sufficient sanction, and therefore, considering the propensities of men to vices, they do not in fact observe it sufficiently.

But it does not seem that it must be called contradictory, as if it were impossible to conceive natural law abstracting from God the legislator, obligation without God willing and commanding : for this is to say too much, and does not seem true.

If it is said that obligation cannot be conceived unless the ultimate end to be attained, concretely considered, is known, which is God ; this alone we think is necessary for complete knowledge of the whole moral law. For partial knowledge the notion of the end abstractly considered, inasmuch as it is the supreme and complete good of rational nature, suffices. — But, even this granted, God would still not be looked at as supreme legislator or as willing and commanding, but only as the Supreme Good to be sought.

249. Remark. — Therefore the eternal law and natural law differ :

1. subjectively : the former is in God, the latter in the created mind ; — and therefore

2. materially in physical being : the former is the (and essence) divine wisdom, the latter is the created light of reason participated from it ; — and consequently

3. in knowability : the former in itself is known by God alone and the blessed, the latter is perceived by the light of reason.

They agree, however : 1° formally and in the reason of dictate, because the rectitude and obligation of both is the same, since one is a participation of the other ; and therefore

2° objectively because they dictate the same, not indeed a) totally according to the whole extension : for the eternal law extends itself also to irrational creatures and to those things which God prescribes by positive law (or orders to be prescribed by others) ; but b) partially : for although not everything that the eternal law prescribes is prescribed by natural law, everything that natural law prescribes is also prescribed by the eternal law. They are therefore the same law, just as the image of the seal and the sealed [thing] are the same ; the seal, however, is more extended than the sealed [thing].