(c) as to subjects. The Eternal Law rules, not only rational creatures (i.e., angels and men), but also irrational creatures, such as matter, plants, and animals. The former are ruled through commands, which require that they direct themselves to their End; the latter are ruled through the inclinations given them by God, which move them to the ends He desires them to attain. Human laws cannot regulate the acts of irrational creatures, for these creatures cannot understand a command as such, and man cannot give them natural inclinations (e.g., it would be foolish to make a law for cats against the catching of birds).
294. The laws to be considered in the pages that follow are temporal and moral. Thus: (a) they are laws promulgated at some particular time, either from the beginning of humanity (as is the case with the Natural Law) or later (e.g., the Mosaic Law, the Christian Law, etc,); (b) they are laws regulating, not the necessary (as is the case with metaphysical or mathematical laws), but the contingent; (c) they are laws given, not to the irrational creature (as is the case with physical and biological laws), but to the rational, that it may attain its end through self-government in accordance with law.
Art. 2: THE NATURAL LAW
(_Summa Theologica_, I-II, qq. 93, 94.)
295. Meaning.—The Natural Law is so called for the following reasons: (a) it is received by man, not through special promulgation, but along with his rational nature. Hence, St. Paul says that the Gentiles, who had not received the laws specially promulgated, were a law unto themselves, that is, through their rational nature (Rom., ii. 14); (b) it includes only such precepts as can be known or deduced from the very nature of man, and thus some pagans fulfilled the Law of Moses naturally, i.e., as regards its natural precepts (Rom., ii. 14); (c) it can be known from the natural light of reason without instruction, being a law written on the heart of man (Rom, ii. 15).
The Natural Law is defined theologically as a participation of the Eternal Law in man. Three elements constitute its essence in its integrity: (a) a passive participation of the Eternal Law consisting in man’s nature and faculties with their inclinations to their proper acts and ends. This man shares with all creatures. (b) an active participation in the Eternal Law proper to man. This consists in the activity of man’s intellect through which he shares in God’s providence and government in a special way as one who can rule himself and others. Reason, reflecting upon the natural inclinations and ordering them to their proper acts and ends, formulates (c) a dictate or command of the practical reason. This command constitutes the essence of Natural Law. “Hence the Psalmist after saying (Psalm, IV. 6): _Offer up the sacrifice of justice_, as though some one asked what the works of justice are, adds: _Many say, Who showeth us good things_, in answer to which he says: _The light of thy countenance, O Lord, is signed upon us_. Thus the Psalmist implies that the light of natural reason, whereby we discern what is good and bad, which is the function of the Natural Law, is nothing else than an imprint on us of the divine light. It is therefore evident that the Natural Law is nothing else than the rational creature’s participation in the eternal law” (_Summa Theol_. I-II, q. 91, a.2).
296. Relation of the Natural Law to Other Laws.-(a) The Natural Law is inferior to the Eternal Law; for, while the Eternal Law exists in the mind of God, underived from any other law and is regulative of all created things, the Natural Law exists in the mind of man, as a derivation and image of the Eternal Law and a rule for man’s acts only. (b) It is superior to Positive Law, for all Positive Law is a deduction from or a determination of Natural Law.
297. Division.—Since Natural Law is the reflection of the eternal plan of Divine Wisdom in the reason of man, we cannot distinguish different species of it according to difference of lawgivers or subjects. The objects regulated are, however, different; and hence we may distinguish various precepts of Natural Law.
(a) According to the difference of persons to whom natural duties are owed, there are natural laws concerning God (e.g., that God must be honored), natural laws concerning self (e.g., that one must not commit suicide), and natural laws concerning the neighbor (e.g., that injustice must not be done).
(b) According to the difference of natural inclinations in man, there are, first, natural laws common to him with all beings (e.g., the law of self-preservation, and hence it is a natural duty of man to take sleep, food, drink, remedies, etc., as necessary for life); secondly, natural laws common to him with all sentient beings or animals (e.g., the law of preservation of the species, and hence it is a natural duty of man to rear and provide for his children); thirdly, natural laws proper to man as a rational being (e.g., the laws that he should cultivate his powers of mind and will, and hence it is a natural duty of man to further religion and education, and to organize into societies and to respect the rights of others).