The Roman world empire, with its toleration of the legal institutions of subject peoples, placed in the hands of the jurists still another important source of knowledge. This was the unwritten ius gentium, which arose out of actual practice and was substantially “found” by the jurists and magistrates. The ius naturale, derived from metaphysical and ethical reflection, appeared identical with the universal element in the legal systems of individual peoples. As the idea of law thus issued from ethical speculation as a teleological apriorism for the positive law, so it emerged as concept of law in the positive law through abstract treatment of the legal systems of particular peoples. This led to the ius gentium. Consequently the results which philosophical thinking arrived at by way of deduction from logos, ratio, and rerum natura turned out to be identical with the idea of law in the systems of positive law. These in turn are products of the universal, law-creating societas humana and of reason that governs in it.
The equating of ius naturae and ius gentium that is met with even in Gaius has here its origin. Ulpian, on the contrary, defined ius naturale as “that which nature teaches to all animals” (quod natura omnia animalia docuit); but this is the ordo rerum. The ius gentium thereupon becomes that part of the ius naturale which has force for mankind.18 This, however, is a product of the will of universal reason, not of the will of some particular historical lawgiver.
The Roman jurists still lacked a clear distinction between law and morality. Even the norm “worship must be paid to God” pertained to law, and so did “live honorably.” To the jurists, indeed, jurisprudence was “a knowledge of things divine and human, the science of what is just and unjust.”19
But the greatest intellectual gain stemmed directly from Stoic ethics. The Greeks, except for a few revolutionary Sophists, had regarded the citizens of the polis as the sole subjects of law. For the Roman jurists, on the other hand, it was not merely the Roman citizen who was in the true sense a subject of law, but every member of human society (the civitas maxima of the Stoics). Therefore they held that man as such is possessed of natural rights, which he continues to retain even in a state of slavery. Slavery was thereby, in contrast to Aristotle’s doctrine, a positive-law institution which could and should be displaced in keeping with being and oughtness.
Even after the revival of imperial sovereignty in the later Roman Empire (under Justinian, A.D. 527–65), the natural law remained the first, supreme, and true legal norm: the basic law of human relations, the model and ideal set before the eyes of the lawmaker for realization. But it was no longer such for the judge, who was henceforth dependent upon the law, or for the citizen. For these the positive law alone had force. Nevertheless the idea of ius naturae had so strong a hold that, in contrast with modern absolutism, as, for instance, in the doctrine of Hobbes, the lawmaker remained subject to the natural law not merely as an empty form, but as a system of content-laden norms.
It remains an eloquent proof of the eternal truth of the doctrine of natural law that Roman law, the finest legal system yet developed in the West,20 enveloped the natural law in its deepest thinking and taught it in its noblest terms.
Like Stoic philosophy, Roman law also passed on this idea to the new Christian era and to the age of scholastic philosophy, which as true philosophia perennis21 has remained the permanent home of the natural law. Scholastic philosophy has been the place of sanctuary for the natural law when arid positivism has driven the latter out of secular jurisprudence. Yet it has always come back into jurisprudence whenever the human mind, weary of the unsatisfying hunt for mere facts, has again turned to metaphysics, queen of the sciences.”22
Everyone is at least familiar with the distinction between legal norm and moral law, even though he does not completely separate them. It must surely have come as something of a surprise, then, that in antiquity such a distinction, let alone a separation, was altogether wanting. Aristotle in his treatise on ethics says that justice, which in this context he takes in the narrower sense, is directed “to another,” and, as essentially concerning the social order, governs the relations of man with his fellow man. But he speaks still more frequently of justice as the general virtue which embraces all others, makes man virtuous, and guides him to the highest goal. He likewise asserts, on this point following Socrates, that the just man is obedient to the laws, i.e., to the written laws and to the unwritten mores. Among these he includes the relations of man to himself, e.g., the curbing of the passions, as well as the ceremonial law and reverence for the divine.
This view rests substantially upon the fact that the sole and exclusive moral fulfillment of the idea of man was held to lie in citizenship. Whence, too, the acceptance of slavery. The slave, it was maintained, is by nature unfitted for citizenship; he is incapable, in the Aristotelian sense, of being educated to virtue. The virtuous life is the goal of man. But he can achieve this goal only as citizen of the polis and in obedience to its laws. All education and training in virtue consequently become politics, and the latter is ethics. The ancients knew only a politico-legal morality. The city-state, in their view, is the ultimate and absolutely supreme pedagogue, the fulfillment of the moral being of man.
The notion of human personality was in its deepest meaning hidden from the ancients, as was also the eternal, superterrestrial goal of the immortal soul. Moreover, they had but a faint idea of a personal God as the supreme lawgiver distinct from the world; nor did they know anything of a Church as the medium of salvation. For them the polis and its divine worship remained the ultimate. Wherever the idea of human rights forced its way through (among the moderate Sophists and in Stoicism), its effect was revolutionary: either it dissolved the city-state or it encouraged dreams of the great society (civitas maxima) of mankind, which of course merely raised the question of its own meaning. Thus the ancients failed to arrive at the distinction between natural law and natural moral law.
Nevertheless, the main problems connected with the idea of natural law existed already in antiquity. The positivism of the Skeptics, of Epicurus, and of Carneades stood in opposition to the natural law in its two recurring forms: the metaphysical one in Plato and Aristotle, and the individualistic one in the earlier Sophists. Furthermore, the continually recurring definitions of law, which have stirred up and divided philosophico-legal thinking down to the present day, had already been formulated: law is will, law is reason; law is truth, law is authority. The doctrine of an original state of nature, of fundamental importance for individualism but of merely persuasive value for other thinkers, appeared already among the Sophists. It appeared also among the Stoics for a similar reason but with another object in view, namely, to provide the basis for a distinction between a primary and a secondary natural law. This distinction, valuable to the Church Fathers in connection with their doctrine of original sin, served the Scholastics to differentiate the self-evident principles of the natural law from the conclusions obtained through reasoning the content of the natural law is more exactly determined—as well as to solve more or less successfully certain thorny theological problems.
The Natural Law in the Age of Scholasticism
A new philosophy and a new world order did not follow at once upon the entrance of the Christian faith into the ancient world, into a sociocultural