and purpose of law as such, has to be realized in every legal system. The natural law is thus the meaning of the positive law, its purpose and its ethically grounded norm.
Recognition of the fact that no system of positive law is altogether perfect brought Aristotle to the principle of equity. The law is a general norm, but the actual matters which it has to regulate issue from the diversity of practical life. Of necessity the positive law exhibits imperfections; it does not fit all cases. Equity thereupon requires that the individual case get its right, i.e., that the imperfection of the formal law be overcome by means of material justice, through the content of the natural law. Thus Aristotle already viewed the judge’s function of filling up gaps in the law as an attempt to apply the natural law—if indeed the positive law is rightly to bear the name of law at all. The gaps are consequently the gateways through which the natural law continually comes into play. In such cases the judge has to decide in accordance with the norm which the true lawgiver would himself apply if he were present; the true lawgiver of course is always assumed to will what is just. This is a celebrated formula which in these very words or in the form, “which he [the judge] would lay down as lawmaker,” still found its way into the great codifications of civil law undertaken in the nineteenth and twentieth centuries (e.g., the Austrian and Swiss Civil Codes).
Concerning the content of the natural law Aristotle had as little to say as Plato. This was in sharp contrast to the Sophists, who because of their political and socio-critical bias had admitted many reform proposals and demands into their natural law. The silence of Plato and Aristotle finds its explanation in their idea of the natural law: they set out from the conservative conviction that the positive law wishes to realize the natural law. Added to this was their strong belief in the excellence of the existing laws of the polis as well as in the conformity of such laws to the natural law. The city-state, its general welfare, and its happiness occupied so prominent a place in the ethical thinking of Plato and Aristotle—for whom indeed the idea of man achieves ultimate perfection in the good citizen—that they looked upon the existing laws as something holy. In contrast to the individualistic attack launched by the Sophists against them, the natural law of Plato and Aristotle served precisely to justify the existing laws and not merely as a basis for criticizing them, although the function of criticism was regarded as included in the idea of natural law. Furthermore, for Aristotle as for Plato the polis or city-state was the great pedagogue, against which, strictly speaking, no natural, subjective right of the citizen could be admitted. They acknowledged no goal of man that transcends the ideal polis. They remained state socialists. Their doctrine of natural law was from the political standpoint conservative, but it was based on metaphysics. With the effective discovery, through Christianity, of human personality and with the recognition of God’s intellect and will as the source of the natural moral law, rational thought would thenceforth be in a position to work its way through to the true natural law.
In the public squares of Athens and on the steps of its public buildings the wordy Sophists had once taught their rationalistic philosophy, their revolutionary natural-law doctrine. In the same places Socrates, the “lover of wisdom,” and Plato and Aristotle, following him, had risen up against the skepticism that was already making its appearance among the Sophists, a skepticism evoked by the doctrine of man as the measure of all things9 and by the resultant subjectivism in epistemology and ethics. This trio of thinkers had anchored anew in philosophy the natural law which at the hands of the Sophists had been threatening to decline into a mere rationalization of political interests.
With the disappearance of these intellectual giants from the scene, however, the Skeptics, the positivists of their day, began at once to hold forth in the same halls and gardens of the Academy at Athens. The senses, they taught, do not convey true knowledge but only illusion; even reason does not guarantee the truth and certitude of knowledge; certainly, then, truth cannot arise from the illusions of both the senses and reason. All laws, whether of art, speech, morality, or right, are arbitrary. They have their origin in mere agreement, and they vary with the change of the free will which establishes them. As no assertion is of more value than its opposite, so, too, no law is worth any more than its opposite. Likewise, since we cannot perceive the essence or nature of things and of man, a natural law is impossible.
Skepticism attained its highest point in the teaching of Carneades (cir. 215–125 B.C.), who for a long time was scholarch at Athens. About 155 B.C., in Rome, he directed his attacks against the natural-law doctrine of the Stoics, a contest which he had made the principal mission of his life. There he won fame through his pro-and-con method of demonstration, whereby he strove to heap ridicule upon the notion of justice. One of his most celebrated arguments was drawn from the borderline case known as “the plank of Carneades.” At a time of shipwreck two persons swim to a plank and grasp it simultaneously. But the plank can hold up and save only one of the two. In the light of this case what is right, and who has the right to the plank? Both and neither, he answered, in such a case of dire necessity and self-preservation. (Seventeen centuries later Suarez furnished the correct solution: the order of justice here terminates, and the order of charity governs the case.) Positivism in ethics and law reached its climax with Carneades, again in connection with the repudiation of objective knowledge of reality and essences and with the denial of metaphysics.
Stoicism prepared the way for the Christian natural law. It was founded in Greece as a school of philosophy by Zeno, who lived from about 340 to 265 B.C. It came to its full flowering in Rome in the imperial age. The great figures of Seneca and the emancipated slave Epictetus as well as the appealing personality of Emperor Marcus Aurelius there adorned the Stoic school. Cicero, however, was its great popularizer, and the wealth of Stoic thought was handed down to the medieval world mainly in his writings. Stoicism, moreover, greatly influenced the various schools of Roman jurisprudence. The passages of Roman law which touch the natural law have their source mostly in Stoic philosophical literature.
Stoicism thus reached its height at a time when the society of the ancient world was definitively splitting into two classes. On the one side stood the plebeian proletariat, kept tractable by largesses of food and other articles and by shows; on the other side stood the new aristocracy and bourgeoisie, largely given over to unrestrained pleasure-seeking and vice. Over both classes, deified and sometimes crazed Caesars eventually established a despotic rule. This environment conditioned the eclecticism of the Stoa, that circle of the few from all ranks and provinces of the world empire who placed the idea of a virtuous life and of attaining happiness of mind through the true, the good, and the beautiful above base sensuality, pursuit of wealth, and pride of life. The Stoics were individualists but, unlike the Sophists, they were not militantly opposed to the polis; indeed, the city-state no longer existed, only the world empire. Therefore they extolled, besides the individual, the social impulses and feelings. They drew upon and assimilated the intellectual goods of Heraclitus, Socrates, Plato, and Aristotle.
The core of Stoic teaching is ethics with its Socratic and, in final analysis, general Greek stamp of intellectualism, according to which correct knowledge is the basis of ethics, and the unity of knowledge and conduct forms the ideal of the sage. This last and most striking representative of the spirit of the declining civilization of antiquity comes closest to the grander representative of Christianity, the saint.
The sage is the man who carries his happiness within himself, who in inner self-sufficiency remains undisturbed by external events. Knowledge and conduct are not dependent on the irregular influences of the world: the sage is calm, unmoved by passion. It is owing to the passions and their excesses that clearness of perception and judgment becomes impossible. For this reason man does not attain to a clear knowledge and judgment of what is truly worth striving for. This consists essentially in conformableness to the rational nature of the sage. Virtue consists in the positive determination of conduct through will power in accordance with rational insight into man’s essential nature. Virtue is right reason. Nature and reason are one. Right reason and the universal law of nature, which holds undisputed sway throughout the universe, are also one. Obedience to the eternal world law in a life lived according to reason: such, embraced with religious fervor, is the ethical principle of Stoicism. It thus means to live in harmony with oneself, to live in accordance with one’s rational nature; for the latter manifests the world law.
Law, too, has its basis in nature. Man has an inborn notion of right and wrong, and law