1. A short treatise on Sophistical Proofs closes the series of Aristotle’s works on logic. His many writings on physics follow. We have no direct interest in these. But to show how his logical ideas shaped his views in this field, I will take the liberty of quoting a passage from Dr. Whewell’s History of the Inductive Sciences, vol. i. sec. 2, “The Aristotelian Physical Philosophy.”
2. “The principal treatises of Aristotle are the eight books of Physical Lectures, the four books Of the Heavens, and the two books Of Production and Destruction. The book Of the World is now universally acknowledged to be spurious. The Meteorologics is full of physical explanations of natural phenomena, but it does not set out the doctrines and reasonings of the schools in so general a form, and the same is true of the Mechanical Problems. The natural-history treatises (On Animals, On the Parts of Animals, On Plants, On Physiognomies, On Colours, On Sounds) gather an extraordinary mass of facts and show a wonderful power of systematising. But they do not expound principles, so they need not be considered here.
3. “The Physical Lectures are the works about which Simplicius, a Greek commentator of the sixth century, and Plutarch both tell a well-known anecdote. Alexander the Great is said to have written to his former tutor: ‘You have not done well to publish these Lectures. How shall we, your pupils, excel other men if you make public what we learned from you?’ Aristotle is said to have answered: ‘My Lectures are published and not published; they will be intelligible only to those who heard them.’ The story may easily have been made up and circulated by people who found the works beyond them. It cannot be denied that working out the meaning and reasoning of every part would be very laborious, if not impossible. But we can follow a large part of the work clearly enough to grasp the character and principles of its reasoning, and that is what I shall try to do.
4. “The author’s introductory account of philosophy fits closely with what has already been said: he takes his facts and generalisations as they are implied in the structure of language. ‘We must in all cases proceed,’ he says, ‘from what is known to what is unknown.’ No one will deny that, but we can hardly follow his inference. He adds, ‘We must proceed, therefore, from universal to particular.’ And he continues that something of this can be seen in language, for names signify things in a general and indefinite manner, as circle does, and by defining we unfold them into particulars. He illustrates this by saying that children at first call all men father and all women mother, and only afterwards distinguish.
5. “Following this view, he tries to settle several great questions about the universe, raised among subtle and speculative men, by unfolding the meaning of the words and phrases applied to the most general notions of things and relations. We have noticed this method already; a few examples will illustrate it further. Rival sects had debated whether there is a void, a place without matter. The arguments were briefly these. There must be a void, because a body cannot move into a space unless it is empty, so without a void there could be no motion. On the other side, there is no void, because the intervals between bodies are filled with air, and air is something. Both opinions had even been supported by experiment. Anaxagoras and his school showed that confined air resists compression, by squeezing a blown bladder and pressing an inverted vessel down into water. On the other side, it was said that a vessel full of fine ashes holds as much water as if the ashes were not there, which could only be explained by void spaces between the ashes. Aristotle decides that there is no void, on an argument like this: in a void there could be no up and down, since in nothing there are no differences, and none in a privation or negation; but a void is merely a privation or negation of matter; therefore bodies in a void could not move up and down, which it is their nature to do. It is easy to see that such reasoning raises the familiar forms of language, and the intellectual connections of terms, above facts. It makes truth depend on whether terms are primitive, and on whether we say that bodies fall naturally. In such a philosophy every new result of observation would have to conform to the usual combinations of phrases, as they had been linked by the modes of apprehension already familiar.
6. “I do not mean to suggest that the common modes of apprehension underlying common language are limited and casual. On the contrary, they imply universal and necessary conditions of our perceptions and conceptions: all things are necessarily apprehended as existing in time and space and as connected by cause and effect. So far as the Aristotelian philosophy reasons from these assumptions it has a real foundation, though even then its conclusions are often insecure. We have an example in the eighth book, where he says there never was a time without change and motion: ‘for if all things were at rest, the first motion must have been produced by some change in some of these things; that is, there must have been a change before the first change.’ Again: ‘How can before and after apply where time is not? or how can time be when motion is not?’ And: ‘If time is a mensuration of motion, and if time be eternal, motion must be eternal.’ But sometimes principles of a more arbitrary kind are brought in, and beyond the general relations of thought, the inventions of earlier speculators are taken for granted, such as the commonly received opinions about the frame of the world. From the eternity of motion, proved as above, Aristotle goes by a curious train of reasoning to identify this eternal motion with the daily motion of the heavens. ‘There must,’ he says, ‘be something which is the first moved,’ which follows from the relation of cause and effect. Then: ‘Motion must go on constantly, and therefore must be either continuous or successive. Now what is continuous is more properly said to take place constantly, than what is successive. Also the continuous is better; but we always suppose that which is better to take place in nature, if it be possible.’ Here the vague judgment of better and worse is introduced, as natural and unnatural had been before into physical reasoning.
7. “I proceed with Aristotle’s argument: ‘We have now, therefore, to show that there may be an infinite, single, continuous motion, and that this is circular.’ This is proved, as one might guess, from the consideration that a body may go on revolving regularly in a circle. So we have a demonstration, on the principles of this philosophy, that there is and must be a first mover, revolving eternally with uniform circular motion. This kind of philosophy may seem too trifling to dwell on, but it is important for our purpose to exemplify it so far, that we may go on knowing we have done it no injustice.
8. “I now pass from the doctrines on the motions of the heavens to those on the material elements of the universe. Here I remark that the tendency we are tracing, to draw speculative opinions from the relations of words, must be very natural to man. The widely accepted doctrine of the four elements seems to rest on the opposition of the adjectives hot and cold, wet and dry. It is much older than Aristotle and was probably one of the earliest philosophical dogmas. But the great master of this philosophy states it more systematically than his predecessors.
9. “‘We seek,’ he says, ‘the principles of sensible things, that is, of tangible bodies. We must take, therefore, not all the contrarieties of quality, but those only which have reference to the touch. Thus black and white, sweet and bitter, do not differ as tangible qualities, and therefore must be rejected from our consideration.’
“‘Now the contrarieties of quality which refer to the touch are these: hot, cold; dry, wet; heavy, light; hard, soft; unctuous, meagre; rough, smooth; dense, rare.’ He then rejects all but the first four, for various reasons. Heavy and light go because they are not active and passive qualities; the others go because they are combinations of the first four, which he therefore infers to be the four elementary qualities.
“‘Now in four things there are six combinations of two; but the combinations of two opposites, as hot and cold, must be rejected. We have, therefore, four elementary combinations, which agree with the four apparently elementary bodies: air is hot and wet (for steam is air), water is cold and wet, and earth is cold and dry.’
10. “This disposition to assume that a common elementary quality must exist wherever we habitually apply a common adjective began before the Aristotelian philosophy and survived its reign. Among other examples, it would be hard to clear Bacon’s Inquisitio in Naturam Calidi, ‘Examination of the Nature of Heat,’ of the charge of confounding very different classes of phenomena under the word hot. The correction of these opinions about the elementary composition of bodies belongs to an advanced period in the history of physical knowledge, even after its revival.
11. “The Aristotelian doctrines on motion are still founded on reasoning from adjectives, but here the result follows not only from the opposition of words but from the distinction between being absolutely and relatively true. ‘Former writers,’ says Aristotle, ‘have considered heavy and light relatively only, taking cases where both things have weight, but one is lighter than the other; and they imagine that in this way they defined what was absolutely heavy and light.’ We now know that things which rise by their lightness do so only because heavier surrounding bodies press them upwards. The assumption of absolute levity is evidently gratuitous, or rather merely nominal, and it vitiated all the reasoning that followed. The inference was that fire must be absolutely light, since it tends to take its place above the other three elements, and earth absolutely heavy, since it tends to take its place below fire, air and water. The philosopher also argued with great acuteness that air, which tends to take its place below fire and above water, does so by its nature, and not by any combination of heavy and light elements. For if air were composed of parts that give fire its levity joined to parts that produce gravity, we could take so large a quantity of air that it would be lighter than a similar quantity of fire, having more of the light parts. It follows that each of the four elements tends to its own place: fire highest, then air, then water, and earth lowest. The whole train of errors comes from verbal fallacies: from taking light as the opposite of heavy, and levity as a quality of a body instead of an effect of surrounding bodies.”