A deeper penetration into the thought of Plato and Aristotle will show, however, that they too distinguish between what is naturally just and what is legally just. Nor is this distinction merely a borrowed formula: it is an integral part of their doctrinal structure. Yet in the case of both we can observe a certain aversion to the “naturally just,” which is accounted for by the Sophists’ abuse of this distinction, an abuse which Plato severely censured.
The disciples of Socrates arrived at the notion of something naturally just by quite another route than the one the Sophists had taken. They arrived at it by way of the doctrine of ideas and through teleological thinking. Following in the footsteps of Heraclitus, Plato acknowledges the world of the senses and the world of ideas that become manifest in intellectual contemplation. For speculative reason, sense phenomena are the bridge of memory to the ideas, which dwell and live on in their supermundane, heavenly abode. The things of this world are or exist only so far as they participate in the being of the eternal ideas, or so far as man in his creative capacity of craftsman, artist, and especially lawmaker copies these ideas. Here teleological thinking enters the scene. In the concept which gropes after and apprehends the essence or the idea of the thing there is contained at the same time also its end, the completion or perfection of the idea of the thing. Inversely, too, the mind lays hold of the essence of a thing by finding the ideal concept which corresponds exactly to the literal meaning. Hence we speak of the true physician, the true judge, the true lawmaker, the true law. These two starting points of Platonic speculation lead then to such conclusions as that the judge ought to be a true judge, i.e., he ought to complete in himself the idea of judge. The ideal concept becomes a norm. So declares the Athenian in Plato’s Laws: “When there has been a contest for power, those who gain the upper hand so entirely monopolize the government as to refuse all share to the defeated party and their descendants. … Now, according to our view, such governments are not polities at all, nor are laws right which are passed for the good of particular classes and not for the good of the whole state. States which have such laws are not polities but parties, and their notions of justice are simply unmeaning.”8 The law should be a true law: one that benefits the common weal. Therein its idea achieves its completion. Thus Plato contrasts the true and proper law with the positive law, and he makes the former the measure and criterion of justice for the latter.
This true law, this true right, abides in the realm of the ideas and remains forever the same. On the other hand, the positive laws change, and they may claim legal force only because and so far as they partake of the idea of law. Indeed they are but a reflection of true law. The lawmaker must look up into the realm of the ideas, where dwells the real essence of the immutable, eternally valid law. However, philosophers and philosopher-kings, freed through disciplined thinking from the blinding illusions of the senses, can alone do this. Moreover, this world of ideas, whereof the world of sense appears only as an imperfect copy, is kosmos, or order; it is not akosmia, or disorder. But this order of the ideas is the pattern for the fashioning of moral and legal conduct in the present world. The being of the ideas is oughtness for man who shapes things in accordance with contemplative knowledge, whether he forms himself or a community unto goodness. Underlying all this, of course, is the conception of a human nature with impaired powers of contemplation. Only the man of disciplined mind, not the great mass of men, can see intellectually. This doctrine is the opposite of the optimism of the Sophists. If Plato, then, scarcely ever makes use of the Sophists’ antithesis of physis and nomos, he by no means identifies the natural law, which he recognizes, with the positive law.
The difference between Plato and the Sophists lies elsewhere. The Sophists started from the freedom of the individual, who had to be liberated from traditional religious and politico-legal bonds. For the polis, the state, is not something eternal, nor is its law. It is mankind that is eternal: the civitas maxima of free and equal men. In the eyes of Plato, however, the polis and its law were the indispensable means for realizing the idea of humanity, which reaches completion in citizenship, in the ethical ideal of the citizen, of the law-abiding and just man. The state is the great pedagogue of mankind. Its function is to bring men to morality and justice, to happiness in and through the moral virtues. Hence Plato’s thought revolves continually around the idea of the best state or government. But this is also why he recognizes a natural law as ideal law, as a norm for the lawmaker and the citizen, as a measure for the positive laws. His metaphysics and the ethical system which he built thereon made a natural law possible and furnished the foundation.
Aristotle passed for centuries as the “father of natural law.” St. Thomas, in that section of his Summa theologica which deals with law, repeatedly appeals to him as the Philosopher par excellence. Aristotle, however, as should now be clear, was not the father of the natural law. Nevertheless his theory of knowledge and his metaphysics have provided ethics, and consequently the doctrine of natural law, with so excellent a foundation that the honorific title, “father of natural law,” is readily understandable.
Plato had totally separated the world of sense perception from the world of pure ideas, the objects of scientific, necessary, and true knowledge (universalia ante rem). Aristotle transferred the idea as the form which determines the formless matter into the individual (universalia in re). This “becomes” through the union of the form (or the essence or the true whatness) with the matter (or the potency or the possibility) and thus gives actuality to the individual. The archetype for Aristotle was human artistic activity: the architect who constructs a house according to the plan in his mind; the sculptor who molds a statue in accordance with his artistic conception; even organic nature which causes the plant to grow from the actualizing essential form that exists in the seed in an incorporeal manner. Aristotle wished to comprehend motion, development, becoming. To him, therefore, the essence, and the perfect expression of it in the individual, is also the telos, or end. The form is thus the efficient and the final cause at one and the same time. Applied to the domain of ethics, however, this means that pure being or the pure essential form is likewise the goal of becoming for the man who is to be fashioned by education into a good citizen. From the essential being results an oughtness for the individual man. In this way, from the content of the primary norm, “strive after the good,” arises the norm, “realize what is humanly good,” as it appears in the essential form of man. The supreme norm of morality is accordingly this: Realize your essential form, your nature. The natural is the ethical, and the essence is unchangeable.
But a criterion of actions is thereby established. Some actions correspond to nature, and hence are naturally good; others are repugnant to nature, and hence are naturally bad. This settled, Aristotle advances to the distinction between what is naturally just and what is legally just. Both are objects of justice. Justice, however, taken in the narrower sense (for in the wider sense the virtuous man is the just man purely and simply) and distinguished from morality, is directed to the other, to the fellow man, whether as equal (commutative justice) or as fellow member of the comprehensive polis-community (distributive and, in the behavior of the member with regard to the whole, legal justice). It finds expression in the natural law and in the positive law. The latter originates in the will of the lawmaker or in an act of an assembly; the natural law has its source in the essence of the just, in nature. That which is naturally right is therefore unalterable. It has everywhere the same force, quite apart from any positive law that may embody it. Statute or positive law varies with every people and at different times. Yet the natural law does not dwell in a region beyond the positive law. The natural law has to be realized in the positive law since the latter is the application of the universal idea of justice to the motley manifold of life. The immutable idea of right dwells in the changing positive law. All positive law is the more or less successful attempt to realize the natural law. For this reason the natural law, however imperfect may be its realization in the positive law, always retains its binding force.