Strange as it may seem at a first glance, it is a very similar trouble that we find with the reasoning of Aristotle. It seems strange, I say, because we are accustomed to associate with Aristotle just those things which would seem to indicate a scientific temper, and to give promise of great results: 1. Extensive accumulation of facts. Many of those works of Aristotle which remain to us are vast treasuries of facts collected from almost every field of Nature, and we have reason for thinking that he made other wonderful collections of facts which have not come down to us. His work has been a standing marvel to all time. 2. Extraordinary powers of reasoning. 3. The fact that he asserted in the strongest terms the need of building up the whole superstructure of knowledge on experience. And yet throughout his works, side by side with the evidences of profound knowledge and profound speculation, there are repeated instances of reasonings which are not only unsound, but altogether puerile—e. g., in the beginning of his treatise on the heavens he proves the world to be perfect by reasoning of the following kind: "The bodies of which the world is composed are solids, and therefore have three dimensions. Now, three is the most perfect number; it is the first of numbers, for of one we do not speak as a number; of two we say both; but three is the first number of which we say all; moreover, it has a beginning, a middle, and an end." That is a fair instance of his scientific incompetency. He has the facts, he is able to reason, but he does not reason according to the facts; he loses sight of them and builds up great arguments on words and names. To give one more example: "He is endeavoring to explain the fact that when the sun's light passes through a hole, whatever be the form of the hole, the bright image, if formed at any considerable distance from the hole, is circular. This, of course, is easily seen to be a necessary consequence of the circular figure of the sun, if we conceive light to be diffused from the luminary by means of straight rays proceeding from every point. But Aristotle attempts to explain the fact by saying that the sun's light has a circular nature which it always tends to manifest. He employs the vague and loose conception of a circular quality instead of the distinct conception of rays" (Whewell).
It is a kind of reasoning which may be applied with great show of success to everything, but which really proves nothing.
And so, as a matter of fact, Aristotle did not leave one single scientific generalization of value to succeeding ages.
Did not the Greeks then do anything in the way of physical science that was to stand? Yes, there was a little work that was exact, and therefore lasting. Archimedes established the fundamental principle on the one hand of the lever, on the other of pressure in fluids—that is to say, laid the stable foundation of the sciences of statics and hydrostatics. Euclid developed, if he did not discover, the law of the reflection of light. Pythagoras discovered, and his followers developed, some of the fundamental principles of harmonics. Greater than any of the others in genuine scientific work was Hipparchus, who, with many erroneous theories, yet really laid the permanent foundation of the science of astronomy. Only one more name need be mentioned among the ancients—that of Ptolemy, who seemed possessed of a genuinely scientific spirit. He accomplished little original work, made no broad generalization (what is known as the Ptolemaic system was in reality the system of Hipparchus), but more than any other of the ancients he is the type of the true scientist in these respects—the accuracy of his observations, the thoroughness of his work at every point, and the really great additions that he made to science in the way of verifying, correcting, and extending the theory he received. He lived in the early part of the second century A. D.
And the next name to attract our notice is that of Copernicus, more than twelve hundred years later. What is the meaning of that lapse of time? After such noble foundations had been laid, was there no great scientific work built thereon in all those centuries? Absolutely none. It will be well for us to think for a moment of what were the reasons for that barrenness, for the same causes are more or less at work at all times to hinder the growth of science and the extension of scientific method.
1. And what strikes us most forcibly at the outset is a lack of the sense of the importance of physical science. Through most of that period Christianity dominated the best thought of Europe, and the tremendous practical problems that confronted the Church for a long time threw everything else into the shade; for a long time, I said, during the early part of this period in especial, when the Church in general seemed to realize its responsibility to win the whole world to its Master, and every individual coming into the Church was made to feel that the Church's work was above everything else in the world. The importance of an exhaustive knowledge of the facts of Nature seemed trifling when compared with questions of character and future life, and making the world feel the power of Christ. Eusebius only expressed the thought of much of his age when he said, speaking of those who pursued the study of physical science, "It is not through ignorance of the things admired by them, but through contempt of their useless labor, that we think little of these matters, turning our souls to the exercise of better things." And with that deliberate turning away from such subjects there would come of necessity that indistinctness of ideas about natural things which is fatal to all scientific investigation. Witness these words of Lactantius: "To search for the causes of natural things; to inquire whether the sun be as large as he seems; whether the moon is convex or concave; whether the stars are fixed in the sky or float freely in the air; of what size and of what material are the heavens, whether they be at rest or in motion; what is the magnitude of the earth, on what foundations it is suspended and balanced—to dispute and conjecture on such matters is just as if we chose to discuss what we think of a city in a remote country, of which we never heard but the name." As Whewell, from whom these last two quotations are taken, says, "It is impossible to express more forcibly that absence of any definite notions on physical subjects which led to this tone of thought."
2. Contributing, without doubt, largely to that indistinctness of ideas, and to the low value put upon physical science, was the mysticism common to the early and the mediæval Church, and to the world at large for many hundred years—the mysticism, that is to say, the habit of assigning supernatural agencies to the various phenomena of Nature, and of regarding them as subject to the vicissitudes of arbitrary will rather than as following out the workings of a consistent orderly plan. There is no need of any attempt to show how fatal such a spirit is to science, nor how that spirit seemed for a long while to dominate the world. "It changed physical science to magic; astronomy to astrology; the study of the composition of bodies to alchemy; and even mathematics was changed till it became the contemplation of the spiritual relations of number and figure." That the Church was not, as has been often charged, responsible for this spiritualizing temper of the age is apparent to any one familiar with the development of Greek philosophy and with the history of the superstitions of the Roman Empire. Nevertheless, it is also true that that temper has been increased in the past and is fostered to-day by the undue emphasis which the Church has placed upon the miraculous character of early Christianity.
3. We notice in the history of the thought of this period, both in the Church and in the world at large, a disposition rather to examine, criticise, and comment upon the work of others, than to do investigating and thinking of one's own. That such a spirit should be found in the Church is not to be wondered at, for the authority of Christ and his apostles would seem to leave no room for originality of thinking on religious subjects, and the sacred Scriptures would give abundant scope for the exercise of the highest learning and of intellectual penetration in interpreting. But the same tendency is noticed outside of the Church, as the great schools of interpreters of Aristotle and of Plato, and the large volumes of abstracts and compilations from preceding writers, bear witness. But when vast learning and ability are expended, rather on such labors than on investigation into the secrets of Nature, science does not thrive.
4. And once again we observe the gradually increasing dogmatic tendency of the Church, the claim to be the repository of all knowledge, the stifling of thought, and of investigation into what might lead men away from the truth and the "faith once delivered to the saints."
It seemed best to give in detail these four evident reasons for the barrenness of science during those centuries, because, as I said, the same things to-day, though with decreasing force, interfere with the progress of science and the extension of scientific method. I shall refer to them again a little further on.