(from An Introduction to Philosophy)
TO EXTRACT the truth latent in Platonism was the mighty reform effected by Aristotle. Aristotle successfully took to pieces Plato's system, adapted to the exigencies of reality the formal principles he had discovered and misapplied, reduced his sweeping perspectives within the limits imposed by a sublime common sense, and thus saved everything vital in his master's thought. He did more: he founded for all time the true philosophy. If he saved whatever was true and valuable, not only in Plato, but in all the ancient thinkers of Greece, and brought to a successful conclusion the great work of synthesis which Plato had attempted, it was because he definitively secured the attainment of reality by the human intellect. His work was not only the natural fruit of Greek wisdom purified from Plato's mistakes and the alien elements included in Platonism; it contained, completely formed and potentially capable of unlimited growth, the body of the universal human philosophy.
Before Aristotle, philosophy may be regarded as in an embryonic stage and in process of coming to birth. Thenceforward, its formation complete, it was capable of indefinite development, and knew no bounds. Inventum philosophicum semper perfectibile.
In fact, Greek speculation after Aristotle had spent its force, and was unable to keep firm hold of the truth. It would receive considerable material enrichment, but in essentials would deform instead of perfecting philosophy.
(a) For twenty years Aristotle was Plato's disciple; but he was a disciple with the equipment of a formidable critic. No one has refuted Plato's idealism more powerfully than he, or more effectively demolished a system which places the substance of things outside themselves. It is perfectly true that the primary object of the intellect is, as Socrates taught, the essences of things; perfectly true also, as Plato had perceived, that the essence of Peter, Paul, or John is humanity or human nature, abstracting from the individual characteristics peculiar to Peter, Paul, or John. But this essence as a universal exists only in the intellect -- in our mind, which extracts or abstracts it from the things in which it exists individualised -- and, on the other hand, it is solely as an object of intelligence (inasmuch as it cannot be conceived apart from certain attributes), and not in its real existence, that it is eternal and necessary. Therefore the essences of perishable things possess no separate existence in the pure state, and the entire Platonic world of archetypal ideas is sheer fiction. The truth of the matter is, as we shall prove later in detail, that there exists in everything an intelligible and immaterial element, which Aristotle calls form, in virtue of which it possesses a specific nature or essence. But this principle is not separate from things; it inheres in them as one of the factors which constitute their substance. Thus individual objects, though mutable and mortal, are no longer deceptive shadows; they are reality.
If real objects of a higher order exist, none are more immediately accessible to our knowledge. If the sensible world be, as it were, an imperfect likeness of the divine life of pure spirit, it is a being which resembles another being, not a mere image which has no existence in itself. If the world is subject to becoming, it is not pure becoming, but contains enduring and substantial realities. If there is no science of the individual object of sense as such, nevertheless a science of sensible reality is possible, because there exists, incarnate, so to speak, in that reality, something intelligible and immaterial.
Thus the corporeal universe is the object not of mere opinion, which can be expressed only by myth and allegory, but of scientific knowledge, the science of physics. Aristotle was the true founder of physics. His incomparably powerful genius viewed mobility in the immutable light of intellect, showed that all change obeys unchanging laws, laid bare the nature of motion itself, of generation and corruption, and distinguished the four species of causation operative in the sensible world. In language strangely trenchant and severe, he sums up his long polemic against the doctrine of ideas. Plato, he argues, completely misconceived the nature of the formal cause when he separated it from things. While he fancied "he was stating the substance of perceptible things," he asserted "the existence of a second class of substances," and his "account of the way in which they are the substances of perceptible things is empty talk; for 'sharing' (participating) means nothing." Plato thus made it impossible to give a satisfactory account of nature, and, by attributing all causation and all true reality to the ideas, he was unable to distinguish in the activity of things the respective parts played by the efficient and the final cause. He thus neglected "the efficient cause which is the principle of change." He further failed to give any account of the cause of "that which we see to be the cause in the case of the arts, for the sake of which mind and nature produce all that they do produce." For "mathematics has come to be the whole of philosophy for modern thinkers, and they profess to explain all other things by mathematics." "And as to motion, if the ideas are motionless," there is no archetype of motion in the world of ideas, but in that case "whence," according to the Platonists, "did motion come? If we cannot explain motion, the whole study of nature has been annihilated."
Refutation of the theory of ideas logically involved the criticism and correction of all the other parts of the Platonic system. In epistemology Aristotle showed that physics, mathematics, and metaphysics, or the first philosophy, are indeed three distinct sciences, but that they are distinguished by their subject-matter, not by the faculty employed, which in all alike is reason. But his most important achievement in this sphere was to prove, by the marvellous analysis of abstraction which dominates his entire philosophy, that our ideas are not innate memories of pre-natal experience, but derived from the senses by an activity of the mind.
In psychology, if in his reaction against Plato's theory of re-incarnation, and from an excessive caution, he refrained from inquiring into the condition of the soul after death, at least he laid the firm foundations of the spiritualist doctrine by proving, on the one hand, in opposition to Plato's dualism, the substantial unity of the human being, composed of two substantial parts incomplete and complementary, and, on the other, against the materialists, the spiritual nature of the operations of the understanding and will. He thus created the only psychology capable of assimilating and explaining the vast material accumulated by modern experiments.
In ethics, by distinguishing between the speculative judgment (which proceeds from the understanding alone) and the practical judgment (which proceeds conjointly from the will), he showed how free will is possible, and how the sinner does what he knows to be evil, and drew, especially in his treatment of the cardinal virtues and in his analysis of human acts, the outlines of what was to be, so far as the natural order is concerned, the ethics of Christianity.
(b) But Aristotle must be studied, not only in his attitude to Plato, but absolutely in his attitude to that which is. For Plato did no more than furnish him with the occasion to wrestle with the problem of being. Aristotle won the match, leaving us his great concepts of potentiality and act, matter and form, the categories, the transcendentals, the causes, as weapons wherewith to wage the same intellectual contest, and teaching us, as a true master of wisdom, to rise above the study of visible and perishable things to contemplation of the living, imperishable reality which knows no change. "Immovable in its pure activity, this being is in no way subject to change. . . . On such a principle depend the heavens and the world of nature. Its life is such as the best which we enjoy, and enjoy for but a short time. For it is ever in this state, since its act is also pleasure -- the act of the supreme intelligence, pure thought thinking itself. . . . If God is always in that good state in which we sometimes are, this compels our wonder; and if in a better, this is yet more wonderful. Life also belongs to God: for the act of thought is life, and God is that act; and God's essential act is life most good and eternal. We say therefore that God is a living being, eternal and perfect, so that life which endures everlastingly belongs to God, for God is this life." Moreover, this God is perfectly one, absolutely single. "Those who say mathematical number is first, and go on to generate one kind of substance after another and give different principles for each, make the substance of the universe a mere series of episodes and they give us many governing principles; but the world must not be governed badly. As Homer observed, the rule of many is not good; one is the ruler."
Thus Aristotle, as Alexander of Aphrodisias remarks in a fine passage of his Commentary on the Metaphysics, "leads us from the things which are themselves on the lowest plane, but most familiar to us, up to the Father, who has made all things, to God the most sublime, and proves that as the founder is the cause of the unity of the globe and the brass, so the Divine Power, author of unity and maker of all things, is for all beings the cause of their being what they are."
Aristotle's mind was at once extremely practical and extremely metaphysical. A rigorous logician, but also a keen-sighted realist, he gladly respected the demands of the actual, and found room in his speculation for every variety of being without violating or distorting the facts at any point, displaying an intellectual vigour and freedom to be surpassed only by the crystalline lucidity and angelic force of St. Thomas Aquinas. But this vast wealth is arranged in the light of principles, mastered, classified, measured, and dominated by the intellect. It is the masterpiece of wisdom, a wisdom which is still wholly human, but nevertheless, from its lofty throne, embraces with a single glance the totality of things.
Aristotle, however, was a profound rather than a comprehensive thinker. He took little care to display the proportions and wide perspectives of his philosophy; his primary object was to apprehend by an absolutely reliable method and with a faultless precision what in every nature accessible to human knowledge is most characteristic, most intimate -- in short, most truly itself. Therefore he not only organised human knowledge, and laid the solid foundations of logic, biology, psychology, natural history, metaphysics, ethics, and politics, but also cut and polished a host of precious definitions and conclusions sparkling with the fires of reality.
It can therefore be affirmed without hesitation that among philosophers Aristotle holds a position altogether apart: genius, gifts, and achievement -- all are unique. It is the law of nature that the sublime is difficult to achieve and that what is difficult is rare. But when a task is of extraordinary difficulty both in itself and in the conditions it requires, we may expect that there will be but one workman capable of its accomplishment. Moreover, a well-built edifice is usually built not on the plans of several architects, but on the plan of a single one. If, therefore, the edifice of human wisdom or philosophy is to be adequately constructed, the foundations must be laid once for all by a single thinker. On these foundations thousands of builders will be able to build in turn, for the growth of knowledge represents the labour of generations and will never be complete. But there can be but one master-builder.
For that reason, in spite of the mistakes, defects, and gaps which betray in his work the limitations of human reason, Aristotle is as truly the philosopher par excellence, as St. Thomas is the theologian.