Front Page Titles (by Subject) QUESTION XCIV.: OF THE NATURAL LAW. - Aquinas Ethicus: or, the Moral Teaching of St. Thomas, vol. 1 (Summa Theologica - Prima Secundae, Secunda Secundae Pt.1)
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QUESTION XCIV.: OF THE NATURAL LAW. - St. Thomas Aquinas, Aquinas Ethicus: or, the Moral Teaching of St. Thomas, vol. 1 (Summa Theologica - Prima Secundae, Secunda Secundae Pt.1) 
Aquinas Ethicus: or, the Moral Teaching of St. Thomas. A Translation of the Principal Portions of the Second part of the Summa Theologica, with Notes by Joseph Rickaby, S.J. (London: Burns and Oates, 1892).
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OF THE NATURAL LAW.
Article II.—Does the natural law contain several precepts or one only?
R. A certain order is found in the things that fall under human apprehension. What first falls under apprehension is being, the idea of which is included in all things whatsoever any one apprehends. And therefore the first principle requiring no proof is this, that there is no affirming and denying of the same thing at the same time; a principle which is founded on the notion of being and not-being; and upon this principle all the rest are founded. As being is the first thing that falls under apprehension absolutely, so good is the first thing that falls under the apprehension of the practical reason. For every agent acts for an end, which end has a character of goodness. And therefore the first principle of practical reason is one founded on the nature of good, good being that which all things seek after. This then is the first precept of law, that good is to be done and gone after, and evil is to be avoided. All the other precepts of the natural law are founded upon this: so that all those things belong to the precepts of the law of nature as things to be done, or avoided, which practical reason naturally apprehends and recognizes as human goods [or evils]. But because good has the character of an end of action, and evil the contrary character, hence all those things to which man has a natural inclination are apprehended by reason as good, and consequently as things to be gone after, and followed out in act; and their contraries are apprehended as evils to be avoided. According then to the order of natural inclinations is the order of the precepts of the law of nature. First of all there is in man an inclination to that natural good which he shares along with all substances, inasmuch as every substance seeks the preservation of its own being, according to its nature. In virtue of this inclination there belongs to the natural law the taking of those means whereby the life of man is preserved, and things contrary thereto are kept off. Secondly, there is in man an inclination to things more specially belonging to him, in virtue of the nature which he shares with other animals. In this respect those things are said to be of the natural law, which nature has taught to all animals, as the intercourse of the sexes, the education of offspring, and the like. In a third way there is in man an inclination to good according to the rational nature which is proper to him; as man has a natural inclination to know the truth about God, and to live in society. In this respect there belong to the natural law such natural inclinations as to avoid ignorance, to shun offending other men, and the like.
Article III.—Are all acts of virtue prescribed by the law of nature?
R. To the law of nature belongs everything to which man is inclined according to his nature. Now every being is naturally inclined to an activity befitting itself according to its form. Hence as the proper form of man is his rational soul, there is a natural inclination in every man to act according to reason; that is, to act according to virtue. Hence from this point of view all acts of virtue are according to nature: for every one’s own reason naturally dictates to him to act virtuously.
But if we speak of virtuous acts in detail, not all virtuous acts are prescribed by natural law: for many things are virtuously done, to which nature at first does not incline, but rational inquiry has found them conducive to human happiness.1
Article V.—Can the law of nature be changed?
R. A change in the natural law may be understood in two ways. One way is the way of addition; and in that way there is nothing to hinder the natural law being changed: for many enactments useful to human life have been added over and above the natural law, as well by the divine law as by human laws. Another conceivable way in which the natural law might be changed is the way of substraction, that something should cease to be of the natural law that was of it before. Understanding change in this sense, the natural law is absolutely immutable in its first principles: but as to secondary precepts, which are certain detailed conclusions closely related to the first principles, the natural law is not so changed as that its dictate is not right in most cases steadily to abide by: it may, however, be changed in some particular case, and in rare instances, through some special causes impeding the observance of these secondary precepts, as has been said above.1
§ 3. There are two ways in which a thing may be said to be of natural law, in one way because nature inclines thereto, as to the axiom that wrong must not be done to another: in another way because nature does not induce the contrary—as we might say that for man to be naked is of natural law, because nature has not given him clothes, but art has invented that addition. Hence Isidore’s saying: “A common possession of all things and one liberty is of natural law:” because slavery and the separation of properties were not induced by nature, but by the reason of men for the utility of human life; and so also in this the law of nature has not been changed except by addition.1
Article VI.—Can the natural law be abolished from the heart of man?
R. Belonging to the natural law are, first, certain most general precepts, which are known to all: secondly, secondary precepts of a more special nature, being conclusions following upon primary principles. As to those general precepts, the natural law can in no way be blotted out from the human heart in the abstract: still it is blotted out in its application to a particular question of practice, inasmuch as reason is hindered from applying the abstract principle to a particular case by concupiscence or some other passion.2 But as to the other, the secondary precepts, the natural law may be blotted out of the hearts of men by evil persuasions, or by vicious customs and corrupt habits, as among some men the note of sin was not attached to robbery, or even to unnatural vice, as the Apostle says.3
[1 ]Thus nature does not prescribe exactly the conduct of a virtuous bankrupt, in what order and proportion he shall pay his various creditors. This and many like points nature rules only in the gross: they need to be further determined by positive law, which therefore is indispensable to humanity. See below, q. 95. art. 2.; and II-II. q. 81. art. 2. § 3. and q. 85. art. 1. § 1. (Trl.)
[1 ]The passage referred to is (art. preced.) as follows: “With all men it is right and meet to act reasonably. From this principle the proper conclusion follows, that deposits are to be restored. And such indeed is the right thing to do in most cases: but it may happen in a particular case that it would be harmful, and consequently unreasonable, if deposits were restored: for instance, if the owner asked them back to assail his country therewith.” See, however, Suarez, De Legibus, l. ii. c. 13. nn. 5—8; and Ethics and Natural Law, pp. 147—152, sect. iii., which follows Suarez. Also II-II. q. 88. art. 10. § 2.; q. 89. art. 9. § 1. (Trl.)
[1 ]See Ethics and Natural Law, pp 280, 281, n. 4: the explanation is important: also p. 360, n. 3. St. Thomas has a similar passage, II-II. q. 66. art. 2. § 1. (Trl.)
[2 ]See above, q. 77. art. 2. (Trl.)
[3 ]Romans i. Ethics and Natural Law, pp. 144—147. (Trl.)