A Beginner's History of Philosophy, Vol. 2: Modern Philosophy

by Herbert Ernest Cushman

Copernicus,	1473–1543, a Pole.
Bruno,	1548–1600, an Italian.
Tycho Brahe,	1546–1601, a Dane.
Kepler,	1571–1630, a German.
Galileo,	1564–1641, an Italian.
Huyghens,	1629–1695, a Hollander.
Newton,	1642–1722, an Englishman.

While the greatest of these scientists is Newton, who belongs to the next period, the most influential is Galileo. Modern methods in science began with Galileo. Of the four predecessors of Galileo three—Copernicus,Tycho Brahe, and Bruno—are in spirit Humanists; for their final explanation of nature is the world of spirits. Kepler belongs to both the Humanistic and Natural Science periods; for at first he constructed his natural science by an amalgamation of the doctrine of spirits and the Copernican theory; but in the latter part of his life he adopted completely the mechanical view of nature. The above scientists may be divided for convenience into two groups: (1) the speculative scientists before Galileo; (2) Galileo and the following empirical investigators.

For fourteen centuries the ancient Ptolemaic astronomy had been regarded by the learned as beyond question. Although complex and unwieldy, it explained all phenomena satisfactorily enough as they appeared to the senses; and it brought phenomena into a system. (The Ptolemaic system has been fully described in vol. i, pp. 322 ff.) To recapitulate it: the world-all was conceived as a hollow sphere with the earth as the centre and the fixed stars in the periphery, while the planets were supposed to move in epicycles. The universe was divided into the heavenly and terrestrial realms, which were occupied by various spirits. God resided outside this hollow sphere and held it, as it were, in his lap.

The history of the changes leading up to our modern astronomical conception makes a vivid chapter. How Copernicus contributed the idea of placing the sun at the centre of things, Kepler the idea of the orbits of the planets as ellipses, Bruno the idea of the boundlessness of space and time, and how Galileo, corroborating these theories by empirical investigations, was put under the ban of the church—all this shows what heroism must have been required to tear down a time-honoredand firmly intrenched traditional conception. Probably the speculative astronomers were not conscious that they were undermining the whole astronomical structure, and probably their sole motive was to simplify the Ptolemaic conception, not to destroy it. For Copernicus accepted the Ptolemaic system, except that he put the sun instead of the earth at the centre, and thereby simplified it by making many of the epicycles unnecessary; and Kepler simplified it further by supplanting the epicycles with ellipses. However, the result was inevitably an entirely new conception of the universe, and with it a new conception of the relation among particular material things. It was in this way that new scientific methods arose.

The universe now comes to be regarded as a mechanism, and what was formerly looked upon as the influence of spirits or as Providential guidance becomes an impersonal law of causal necessity. In the heavens above and the earth beneath there are no longer vital forces and supernatural influences. The universe becomes a homogeneous whole throughout, in which there is no difference between the fall of an apple and the revolution of the planets, no distinction between terrestrial and celestial spheres. The Christian heaven is nowhere in it; the Mediæval spirits are banished from it. The Greek gods have been pushed out, and the Christian God has been made to stand aside.

The demand that the new conception of the universe be verified in concrete experiments, if it were to replace the old Ptolemaic system, the revival of the study of Archimedes, the rivalry in trade and inventions among the Italian towns, were three causes for the demand for greater exactness. Investigation, experiment, and inventioncame into vogue. Magic, alchemy, astrology, and conjurations were no longer accepted as serious methods. In the Middle Ages deduction had been purely the logical employment of the syllogism in theological discussions, while induction, so far as it was used at all, had been the reference of nature phenomena to spiritual forces. Now deduction and induction[6] come to be used for other purposes, and mathematics is necessarily conjoined with both. The new Natural Science period is essentially a “strife of methods”; it is the period when the true plan of scientific procedure is being determined. It is here that the importance and influence of Galileo is seen upon modern science and philosophy.

The influence of mathematics in modern times grew up from these astronomical beginnings among the Humanists; and the Natural Science period with its contention as to methods was the immediate result. Bacon, for example, regarded final causes as one of the “idols.” Hobbes maintained that physics has only to do with efficient causes; Descartes held that it is audacious in man to think of reading the purposes of God in nature; while Spinoza thought it absurd to attribute divine purpose to nature. By degrees everything in nature came to be regarded as a mechanism, and there was no distinction between the animate and the inanimate. The discovery of the mechanical circulation of the blood by Harvey, in 1626, became a vigorous impulse toward the mechanical study of animal life. Descartes regarded animals as complex automata and on this line he published essays on dioptrics, musical law, and thefœtus. Hobbes applied mechanical law to psychological phenomena. The study of reflex action was carried on with great vigor in the Low Countries and France. The mechanical theory was rendered complete in this early time by the exclusion of the soul from the explanation of the body of man, just as God had been pushed into the background of the universe.

Galileo Galilei (1564–1641).[7] The dates of the life of Galileo show him to have been a younger contemporary of Bruno, and, like Bruno, to have been a victim of the ecclesiastical reaction that was sweeping away all scientific freedom in Italy. But while Bruno belonged both chronologically and in spirit to the first period of the Renaissance, Galileo is the true beginner of the second period. Bruno was a philosopher of nature, while Galileo was a true scientist. Galileo gave to all future thought a wisely formulated method of dealing with the new materials of the nature world. His laws of projectiles, falling bodies, and the pendulum created a new theory of motion. He set the hypothesis of Copernicus upon an experimental basis and made the future work of Newton possible. He was professor at the Universities of Padua and Pisa, and he was mathematician and philosopher at the court of Tuscany. That he perjured himself and thereby saved his life from the Inquisition, there is no doubt; but instead of death he had an old age of great bitterness. He gave open adherence to the Copernican system in 1610, when he constructed a telescope and discovered the satellites of Jupiter; and after this there followed discovery afterdiscovery, like the spots on the sun and the phases of Venus, which latter discovery confirmed the Copernican hypothesis. He invented the hydrostatic balance, the proportional compass, the thermoscope, microscope, and telescope. His two most noteworthy writings are The Dialogue concerning the Two Most Important World-Systems, and Investigations into Two New Sciences.

As to method, Galileo objected to formal logic, that it is not a means of discovering new truth, although valuable as a corrective of thought. New truth is discovered when we frame an hypothesis from certain experiences, and then infer the truth of other cases from that hypothesis. The hypothesis is first formed by induction from a few characteristic cases; the inference to other cases is made by deduction. He therefore linked induction and deduction closely together, and conceived them as necessarily complementary in scientific investigation. Either induction or deduction alone is absurd and impossible. By induction alone we should be obliged to examine all cases, an impossible undertaking. By deduction alone we should be in the same straits as the Scholastics, and never discover new laws. We must begin with our perceptual experiences and make an induction from them; then we must bring mathematics into use in constructing the hypothesis from which to deduce (calculate) new cases. This is the true, modern method and reveals the great genius of Galileo.

A mathematical law never exactly coincides with any particular concrete relations. A mathematical law is an hypothesis or ideal construction. What value, then, has a mathematical law for science? The orbits of planets[8]are described as ellipses, but no actual planet moves in a perfect ellipse. The ellipse is an hypothetical, mathematical orbit for a planet which has no disturbing influences upon it. We get at such a law by the method of concomitant variations;[9] and the value of it consists in the simplification and system that it gives the facts. For example, knowing that a planet would move in an ellipse if it suffered no perturbations, and then knowing the influences upon any particular planet, we can calculate its orbit. Mathematical law, although ideal, is the common rule under which all nature phenomena can be brought. However, only by measurements founded on the tests of observation and experiment can we know how far the claims of such deduction are supported. Measure everything measurable, and calculate the measurement of those things not directly measurable.