§ 15 Physical or Scientific Law
Physical laws or the laws of science are expressions of the uniformities of nature—general principles expressing the regularity and harmony observable in the activities and operations of the universe. It is in this sense that we speak of the law of gravitation, the laws of the tides, or the laws of chemical combination. Even the actions of human beings, so far as they are uniform, are the subject of law of this description: as, for example, when we speak of the laws of political economy, or of Grimm’s law of phonetics. These are rules expressing not what men ought to do, but what they do.
Physical laws are also, and more commonly, called natural laws, or the laws of nature; but these latter terms are ambiguous, for they signify also the moral law; that is to say the principles of natural right and wrong.
This use of the term law to connote nothing more than uniformity of action is derived from law in the sense of an imperative rule of action, by way of the theological conception of the universe as governed in all its operations (animate and inanimate, rational and irrational) by the will and command of God. The primary source of this conception is to be found in the Hebrew scriptures, and its secondary and immediate source in the scholasticism of the Middle Ages—a system of thought which was formed by a combination of the theology of the Hebrews with the philosophy of the Greeks. The Bible constantly speaks of the Deity as governing the universe, animate and inanimate, just as a ruler governs a society of men; and the order of the world is conceived as due to the obedience of all created things to the will and commands of their Creator. “He gave to the sea his decree, that the waters should not pass his commandment.”38 “He made a decree for the rain, and a way for the lightning of the thunder.”39 The schoolmen made this same conception one of the first principles of their philosophic system. The lex aeterna, according to St. Thomas Aquinas, is the ordinance of the divine wisdom, by which all things in heaven and earth are governed. “There is a certain eternal law, to wit, reason, existing in the mind of God and governing the whole universe.... For law is nothing else than the dictate of the practical reason in the ruler who governs a perfect community.”40 “Just as the reason of the divine wisdom, inasmuch as by it all things were created, has the nature of a type or idea; so also, inasmuch as by this reason all things are directed to their proper ends, it may be said to have the nature of an eternal law.... And accordingly the law eternal is nothing else than the reason of the divine wisdom regarded as regulative and directive of all actions and motions.”41
This lex aeterna was divided by the schoolmen into two parts. One of these is that which governs the actions of men: this is the moral law, the law of nature, or of reason. The other is that which governs the actions of all other created things: this is that which we now term physical law, or natural law in the modern and prevalent sense of that ambiguous term.42 This latter branch of the eternal law is perfectly and uniformly obeyed; for the irrational agents on which it is imposed can do no otherwise than obey the dictates of the divine will. But the former branch—the moral law of reason—is obeyed only partially and imperfectly; for man by reason of his prerogative of freedom may turn aside from that will to follow his own desires. Physical law, therefore, is an expression of actions as they actually are; moral law, or the law of reason, is an expression of actions as they ought to be.
This scholastic theory of law finds eloquent expression in the writings of Hooker in the sixteenth century. “His commanding those things to be which are, and to be in such sort as they are, to keep that tenure and course which they do, importeth the establishment of nature’s law.... Since the time that God did first proclaim the edicts of his law upon it, heaven and earth have hearkened unto his voice, and their labour hath been to do his will.... See we not plainly that the obedience of creatures unto the law of nature is the stay of the whole world.”43 “Of law there can be no less acknowledged, than that her seat is the bosom of God, her voice the harmony of the world, all things in heaven and earth do her homage.”44
The modern use of the term law, in the sense of physical or natural law, to indicate the uniformities of nature, is directly derived from this scholastic theory of the lex aeterna; but the theological conception of divine legislation on which it was originally based is now eliminated or disregarded. The relation between the physical law of inanimate nature and the moral or civil laws by which men are ruled has been reduced accordingly to one of remote analogy.