CHAPTER VII.
THE NATURAL PHILOSOPHY OF ARISTOTLE.
Aristotle has now done with Practical and Constructive Science.[1] He turns from Man with his disputations, reasonings, oratory, poetry, moral and social life, to the subjects of Speculative Science,—to Nature, the Universe, and God. In glancing at the series of great treatises in which the results of his thoughts and researches upon these subjects are embodied, it will be convenient to divide them under the three heads of Natural Philosophy, Biology, and Metaphysics. First, then, the ‘Physical Discourse,’ the treatise ‘On the Heavens,’ that 'On Generation and Destruction,’ and the ‘Meteorologies,’ form together a distinct whole,[2] and contain the Natural Philosophy of Aristotle, of which let us now notice some of the salient points, leaving his Biology and Metaphysics to form the subject of future chapters.
Natural Philosophy, as conceived by Aristotle, was far more metaphysical than the science which is called by that name in the present day—a science based on mathematics, and starting, we might perhaps say, with the doctrines of Newton’s ‘Principia,’ anything which lies beyond these doctrines being taken for granted. But in Aristotle’s Natural Philosophy nothing is taken for granted. He commences by inquiring into the nature of “Existence;” and sets himself to answer some of the puzzles with which his predecessors, the philosophers of Greece, had racked their own and other people’s brains. They had said, “How is it possible for anything to come into existence? Out of what can it come? It must come either out of the existent or the non-existent. But it cannot come out of the existent, else it would have existed already; nor can it come out of the non-existent, for out of nothing nothing can come.” Aristotle solves this dilemma (‘Phys.’ I. viii.) by introducing what now seems a simple enough distinction—that between the “possible” and the “actual;” things come into existence, that is, into actuality, out of the state of the possible. Now the possible, or potential, is in one sense non-existent, as it is nothing actual; but, on the other hand, it is not mere nonentity, as it is by hypothesis a possibility of existence. All this may appear to be a mere matter of words; and it may be asked what we gain by having the words “possibility” and “actuality” added to our, vocabulary? But, in fact, men think by means of words; and if a new formula can clear up the notions connected with such often-occurring terms as “is” or “became,” it is a gain, the reality of which is shown by the perplexities to which thinkers had been reduced to for the want of it.Aristotle, pursuing his general reflections about Existence, says that in everything that exists you can trace three principles: the Matter out of which the thing arose, and which contained the possibility of its existence; the Form or actual nature which the thing possesses; and the Negation or Privation of all other natures. That is to say—a thing is what it is by not being what it is not. And thus all existence has a negative, as well as a positive, side ('Phys.' I. ix.) These remarks form a metaphysical basis to Natural Philosophy.
In the second book of his 'Physical Discourse,' Aristotle quits the region of pure abstractions, and states, in interesting terms, his views of "Nature." He speaks of "Nature" as "a principle of motion and rest essentially inherent in things, whether that motion be locomotion, increase, decay, or alteration." "It is absurd to try to prove the existence of Nature; its existence is self-evident." "Nature may be said in one way to be the simplest substratum of matter in things possessing their own principle of motion and change; in another way it may be called the form or law of such things." In other words. Nature is both "matter or potentiality, and form or actuality; both the simple elements of a thing and its existence in perfection. It is also the transition from the one to the other. "Nature," says Aristotle, "spoken of as the creation of anything, is the path to nature."
Paley's 'Natural Theology' opens with the celebrated argument which compares the world to a watch. "If one were to find a watch," says Paley, "he would surely conclude that there must have been a watchmaker; and so from the marks of design in creation, which are like the adaptations to special purposes of each part in the watch, we must conclude that an intelligent Creator made the world." Aristotle, quite as strongly as Paley, admits the marks of design in nature. He says ('Phys.' II. viii. 14.): "The adaptation of means to ends which we see in the procedure of the animals makes some men doubt whether the spider, for instance, and the ant, do not work by the light of reason or an analogous faculty. In plants, moreover, manifest traces of a fit and wisely planned organisation appear. The swallow makes its nest and the spider its web by nature, and yet with a design and an end; and the roots of the plant gi'ow downward for the sake of providing it with nourishment in the best way. It is plain, then, that the origin of natural things must be attributed to design." He repudiates the notion that "the heavens and the divinest of visible things" ('Phys.' II. iv. 6) can have been the result of the workings of blind chance. Nor will he accept the theory of Empedocles (which was like the Darwinian theory of Natural Selection in its extremest form) that blind chance hit upon the production of life, and that whole races of monsters and imperfect beings perished before the moment came when—by mere accident and coincidence—a creature was attained sufficiently perfect to survive ('Phys.' II. viii. 4). So far from chance having been the chief force in producing the framework of the Universe, Aristotle considers chance to be a mere exception, a mere irregularity, thwarting the reason and the wisdom which guides, and has ever guided, the operations of nature.
But, while utterly denying what Mr Darwin would seem to point to—that Reason is a result of the functions of matter, and is a comparatively recent development in the history of this globe—Aristotle would equally deny the thesis of Paley, that Reason, in the form of an intelligent Creator, existed separately before this world, and constructed the world as a watchmaker constructs a watch. While he considered Reason to have existed from all eternity, he thought that the Universe, pervaded in all its parts by Reason, had also existed from all eternity. Thus all idea of the world having been created was quite eliminated from the thoughts of Aristotle. He said the world must have been eternal, for everything which is created, or comes into existence, comes into the "actual" out of the "possible." The egg and the seed are instances of the "possible," the fowl and the flower of the "actual." But there must always have been a fowl before there was an egg, and a flower before there was a seed. Therefore the actual must always have been first; and if this be the case with particular classes of things, we cannot conceive that the whole world was ever non-existent, and a mere possibility waiting to be called into existence ('Metaphys.' VIII. viii.)
Philosophers always acknowledge the difficulty which there is in conceiving a beginning. Aristotle escapes this difficulty by asserting that the Universe has existed eternally the same as it appears to us now. He says that there is only one Cosmos or Universe, and that outside of this there is “neither space, nor vacuum, nor time.” One would expect these words to mean that the Universe extends to infinity in all directions; but, on the other hand, Aristotle attributes a definite circular shape to the “outside” of the Universe, which would be incompatible with the idea of infinite extension. In fact, his arguments to prove the above untenable position are curious abstract quibbles, which may be quoted to show how oddly a philosopher of the 4th century B.C. could reason on the physical construction of the Universe. He says (‘On the Heavens,’ I. ix.) that there can be neither space nor vacuum outside the circumference of the Cosmos, for, if there were, then body might be placed therein; but this is impossible, because every physical body is naturally endowed with one of three motions: it is either naturally centripetal, or naturally centrifugal, or naturally revolving round the earth. Now each of these three kinds of body has its natural place within the Universe; the stone being centripetal has its natural place on or in the earth; fire being centrifugal has its natural place above the air; the stars which revolve have their natural place in the revolving Heaven. Thus there is no kind of body which can naturally exist outside the Universe, and therefore there can be no Space, for Space is that in which bodies exist! That there is no Time beyond the limits of the Universe, Aristotle proves by the more legitimate argument that “if there is no motion there can be no time, since Time is the measure of motion.” But his conception of the “natural” motions inherent in different classes of bodies, and his appeal to his own preconceived ideas of "nature" to prove what exists, or does not exist, outside the circumference of Heaven, are very characteristic.
Time and Space, then, according to Aristotle, end with the circumference of Heaven, though it is difficult to understand how space can he conceived to come to an end at any particular point. But the Stagirite here becomes mystical, for he says that, "the things outside," existing in neither space nor time, enjoy for all eternity a perfect life of absolute joy and peace ('Heavens,' I. ix.) This is the region of the divine, in which there is life and consciousness, though perhaps no personality; it is increate, immutable, and indestructible.
Descending from this region—if that can be called region which is out of space altogether—we come in the Aristotelian system to the "First Heaven," the place of the fixed stars, which ever revolves with great velocity from the left to the right. In a lower sphere, revolving in the contrary direction, are the sun, moon, and planets; and we are told that we must not suppose that either stars or planets are composed of fire. Their substance is ether, that fifth element, or quinta essentia, which enters also into the composition of the human soul. They only seem bright, like fire, because the friction caused by the rapidity with which they are carried round makes them red-hot. The reason why the stars twinkle, but the planets do not, is merely that the former are so far off that our sight reaches them in a weak and trembling condition; hence their light seems to us to quiver, while really it is our eyesight which is quivering. Sun, moon, and stars alike are living beings, unwearied, and in the enjoyment of perfect happiness.
It has often been said that if an ancient Greek temple be compared with a Gothic cathedral, the one suggests the idea of the finite, the other of the infinite. The same thing might be said of Aristotle's Cosmology when compared with the views of modern science. Aristotle figured to himself a perfectly limited universe, with the earth in the centre, and the fixed stars all round the circumference. In a circle, or globe, it may be questioned which is the place of honour—the centre or the circumference. The Pythagoreans, accordingly, after the abstract method of those times, declared that the centre must be the most honourable position, and that, as the element fire is more honourable than the element earth, the centre of the Universe must be occupied by some Central Fire, and that the earth must revolve round this like the other stars. Aristotle, unconscious how much nearer to the truth this guess was than his own, laughs at it as the production of men "who try to square facts to their own fancies, and who wish to have a share in the arrangement of the Universe." He also repudiates ('Heavens,' II. xiv. 1) the theory of Plato that the earth is packed round the axis of the entire Universe and revolves with it, thus causing day and night.[3] He maintains that the earth is the motionless centre, but the least honourable member, of the Universe, the all-embracing circumference being the most noble, and the heavenly bodies having a dignity in inverse ratio to their approach towards the centre. The guesses, or intuitions, of the ancient Greeks in Aristotle's time, or soon afterwards, hit upon something very like an anticipation of the Copernican system. And this was especially the case with Aristarchus of Samos, who announced the double movement of the earth, round its own axis and round the sun. But Aristotle certainly contributed nothing towards the adoption of such ideas. He unfortunately committed himself, on fancied grounds of symmetry, to an opposite view.
Aristotle argued that if the earth were to move it could only do so "unnaturally," by the application of external force in contradiction to its own natural tendency to rest round the centre, and that no such forced movement could be kept up for ever, whereas the arrangements of the Cosmos must be for all eternity. Therefore the earth must be at rest! As to its shape, Aristotle was more correct: he proved it to be spherical—(1) by the consideration that all heavy bodies are by nature always tending to the centre, and that this process must result in the production of a spherical mass; (2) by the fact that the earth's shadow cast on the moon in an eclipse is circular. He considered the bulk of the earth to be small when compared with that of "the other stars;" he accepts the calculations of the geometers of his time that its circumference was 400,000 stades; and he says that "we must not treat with incredulity the opinion of those who say that the regions near the Pillars of Hercules (or Straits of Gibraltar) join on to India, and that the ocean to the east of India and that to the west of Europe are one and the same." In support of this proposition he adduces the fact that elephants are to be found on each side, i.e. in India and in Africa ('Heavens,' II. xiv. 15). The passage of Aristotle here quoted had a large share in inflaming the imagination of Christopher Columbus, and in sending him forth from the coasts of Spain in search of the coasts of India; and it was the cause of the islands of Central America being named the "West Indies," and the aborigines of North America being called "Red Indians." As an approximative guess at the size and figure of the earth, the passage in question was not a bad one, considering the time when it was written; but curiously enough it contains two errors, the first of which would imply the earth to be a great deal larger, and the second a great deal smaller, than it really is. The mean geographical stade of the Greeks is computed at 168 yards 1 foot and 6 inches, and thus if 400,000 stades be assigned to the circumference of the earth, we get a measurement of above 38,000 miles, whereas the latest calculations would only give about 24,857 miles for a mean circumference of the earth. Thus evidently the geometers of the time of Aristotle were too liberal in their ideas of the earth's size. But, on the other hand, those who identified the Atlantic with the Pacific Ocean, and brought India opposite to Spain, had evidently too contracted a notion of the contents of our globe.
Owing to the absence of astronomical instruments, and the generally infantile condition of physical science in the 4th century B.C., it was only natural that the a priori method, or guessing, should greatly predominate in the cosmical theories of that time. But Aristotle’s strength did not lie in his imagination. In this faculty he was inferior to other philosophers whom in analytical power he far surpassed. Thus Alexander von Humboldt says of him (‘Cosmos,’ vol. i. note 48), “the great influence which the writings of Aristotle exercised on the whole of the Middle Ages, renders it a cause of extreme regret that he should have been so opposed to the grander and juster views of the fabric of the universe entertained by the more ancient Pythagorean school.” There was, in fact, a want of sublimity in the fancy of Aristotle, and it so happened that he sometimes contemptuously rejected hypotheses which were not only more beautiful, but more true, than his own. We have seen that this was the case with regard to the earth’s position in the cosmical system. And the same thing occurred as to the nature of comets. The Pythagoreans had declared comets to be “planets of long revolution;” but Aristotle, rejecting this supposition, affirmed them to be transient meteors of our atmosphere, formed out of luminous or incandescent matter which had been thrown off by the stars. And to explain the reason why comets are so rare, he said that the matter out of which they are composed is constantly used up in forming the Milky Way. (‘Meteorol.’ I. viii.) “The nebulous belt, then, which traverses the vault of the heavens, is regarded by the Stagirite as an immense comet incessantly reproducing itself.”
Clearly, Aristotle’s contribution to Natural Philosophy did not consist in suggesting or leading the way to true views as to the nature and arrangement of the heavenly bodies. He not only was not in advance of his age in this respect, but was even behind it, in so far as he refused to adopt theories, which have since turned out to have been anticipations of the results of modern science. But, on the other hand, it must be remembered that those theories were incapable of verification at the time, and had no force in themselves to command the attention of the world. They were like the “false dawn” in tropical countries, which appears for a few minutes and then fades way, allowing the darkness again to reign supreme, till the true sunrise takes place. Unconvinced by the speculations of the Pythagorean school and of Aristarchus of Samos, the great Alexandrian astronomer, Ptolemy, in the second century of our era, reaffirmed the Aristotelian views as to the spherical form and motion of the heavens, as to the earth’s position in the centre of the heavens, and as to its being devoid of any motion of translation. And the Ptolemaic system satisfied men’s minds until, with Copernicus and Galileo, modern astronomy began.
We must allow that Aristotle’s cosmical ideas were erroneous and misleading. Still we must take them as constituting a mere fraction of his encyclopædia of philosophy, and we must recollect that they are put forth in works which laid out and constituted new sciences. This was the Stagirite’s achievement,—the clear analytic separation of the different sciences, and the statement, in outline at all events, of the questions which each science had to answer. Aristotle generally attempted to furnish his own answer to these questions, and often gave wrong answers; yet to have posited the questions at all was a great matter, and cleared the way for the thoughts of subsequent generations. There is no one to whose work the saying is more appropriate than to that of the Stagirite—prudens quæstio dimidium scientiæ est—“It is half-way to knowledge when you know what you have to inquire.”
The leading questions started in the Natural Philosophy of Aristotle are as to the nature of causation, time, space, and motion. On the subject of motion he went astray by taking up the idea that celestial and terrestrial motions were different in kind—that the heavenly bodies “naturally” revolved, while bodies on earth had each a natural motion in them, either downward or upward. This belief in the absolute levity of certain bodies—as, for instance, fire—was, of course, a mistake. “Truth is the daughter of Time;” and a few of the great discoveries of modem ages, which appear so simple, though they were so hardly and so late achieved,—such as the Copernican system, and the law of gravitation,—have shattered the Cosmos of Aristotle. Still it required at least fifteen centuries before anything like a demonstration was brought against the reality of that Cosmos and its arrangements. Thus, if Aristotle be censured for the incorrectness of his theories, succeeding generations of thinkers for so long a period must also be held responsible for their undoubting acceptance of them.
Aristotle’s method in Physics, as in most other subjects, consisted in this: he first endeavoured to state clearly to himself what was the problem which he had before him, then he collected all the solutions of that problem which had been proposed by his predecessors, and all popular “sayings” and “notions” in regard to it, and then he examined existing opinions by the light of such facts as occurred to him, or which had been previously collected by him, or else he applied logical reasonings and general philosophical considerations in pronouncing upon the validity of the theories of others. A main part of the process consisted in starting ingenious difficulties to the theories in question, so that they seldom came through the ordeal without being wholly exploded or considerably modified. The residuum left, or the new result arrived at, constituted the theory of Aristotle. Such is not the procedure by which discoveries are made, knowledge increased, and the boundaries of science extended, in modern times. But after all, it was not a bad procedure for a man who was writing an encyclopædia. Aristotle had undertaken to set forth every department of knowledge revised and perfected, so far as possible, by the aid of stores of information and thought which he had laid up. In some departments he was much stronger than others: in Politics, Sociology, Psychology, and Natural History, he had a far better array of facts than in Astronomy and Mechanics. No one could be keener than he was to make facts the basis of every theory; but he was obliged to do the best he could in each case with his materials. He set out all that was known or believed on each subject, and added to the knowledge or criticised the beliefs as well as he could. The real aids for the advance and verification of science which exist in modern times— instruments, such as the telescope, the microscope, the barometer, the thermometer, the spectroscope, and countless others; the knowledge of many great laws of nature; and the practice of accurately observing and carefully recording,—were all wanting in the days of Aristotle. Therefore it is absurd to treat him as if he had been a modern man of science, with a vicious method. It may be called a mistake that he attempted so much; still what he accomplished was wonderful if we merely regard it as a map of the Sciences belonging to the 4th century b.c., full of his own additions and improvements.
There is one great science of modern days which Aristotle failed to separate off, or sketch out, or in any way to foreshadow — and that is the science of Chemistry. Some erroneously spell this word “chymistry” as though it were derived from the Greek chymos, [4] a juice, and as though it had been known to the Greeks. But of course “chemistry” comes from the Semitic word chem (which is the same as “Ham,” the son of Noah), meaning “black,” and then “Egyptian.” And thus Chemistry is the black or Egyptian art, having taken its rise out of the searches made by the Alchemists to discover the philosopher’s stone. Aristotle had no notion whatever of the rich field of knowledge and power which lay in the analysis of substances. He had no idea of the composition of water or air. The crucible and the retort had never been worked in Athens; the most superficial guess-work, as to what we should call the chemical properties of bodies, contented the philosophers of the day. Aristotle’s work ‘On Generation and Corruption’ would have been the appropriate place for enunciating some of the laws of Chemistry; but he does not go beyond a resolution of the “Four Elements” into the ultimate principles of the Hot, the Cold, the Wet, and the Dry—the first pair being “active” and the second “passive” principles. Hot and Wet, we are told, form Air; Hot and Dry, Fire; Cold and Wet, Water; Cold and Dry, Earth. From these principles Aristotle deduces the generation and destruction of physical bodies; but on the details of a theory which now seems puerile we need not dwell.
- ↑ See above, p. 42.
- ↑ On the connection of these works see some general remarks above, pp. 45, 46.
- ↑ There is some doubt as to what Plato's theory actually was. See 'Minor Works of George Grote,' vol. i. pp. 239-275, and Professor Jowett's Introduction to the 'Timaeus' of Plato.
- ↑ Aristotle, in treating of the sense of Taste, gives an enumeration of different flavours, and then says, “The other properties of juices form a proper subject for inquiry in connection with the physiology of plants.” Thus by “juices” he means vegetable fluids, to be treated of from the point of view of Botany or of Materia Medica.