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he created a new science. Instead of Aristotle's guiding reason, which was 

 in reality nothing but an expression for the speculating philosopher's own 

 inferences, deducted for the most part from purely human-cultural hypotheses 

 Galileo brings the phenomena of motion on the earth under one common 

 law, which operates out of mathematical necessity and whose manifestations 

 can under given conditions be calculated in advance, just as at an earlier 

 epoch it had been possible to calculate the regular path of the "divine" 

 heavenly bodies. Galileo was, it is true, unable to find one common law 

 governing the motions of terrestrial objects and the heavenly bodies — that 

 was for Newton to find in his law of gravitation — but Galileo laid down 

 the principle governing the natural-scientific treatment of terrestrial phe- 

 nomena, a principle which he expressed in the words: "To measure what can 

 be measured and to make measurable what cannot be measured." He seeks a 

 mechanical reason for everything that happens — a force that sets things 

 in motion. To refer to God as the cause of natural phenomena serves no pur- 

 pose, in his opinion, for one can attribute anything whatever to the will of 

 God, since no necessity underlies it. According to Galileo, natural science 

 should compare material things merely with one another, not with super- 

 natural things, and at the same time it has to be remembered that nature is 

 itself a miracle, although its phenomena have a natural explanation. In 

 actual fact, gravity is merely a word for something which we do not know; 

 we cannot tell what it is that attracts stones to the earth. Galileo sees clearly 

 that it is useless to try to find out what the forces of nature are; the scientist 

 can only discover how they operate. 



Galileo' s victory over Aristoteleanism 

 Such a complete revolution of the aims and methods of natural science as 

 that carried out by Galileo could not of course penetrate men's minds all 

 at once. He himself fell a victim not only to the Church's intolerance, but 

 also to the superstitious respect in which the Renaissance held the culture 

 of antiquity and its chief scientific authority, Aristotle. Actually another 

 century was to pass before Aristoteleanism in every field of human knowledge 

 was successfully eradicated from the ideas underlying the science of the pres- 

 ent day. In order to rid natural science of Aristotelean fallacies it was, in 

 fact, necessary to destroy Aristotle's entire thought-system, and this was first 

 done during the seventeenth century by the great systematic thinkers of that 

 period, Descartes, Spinoza, and Leibniz, who will be discussed later on. We 

 shall now proceed to a survey of what the Renaissance period achieved in 

 the way of pure biological research, not only in the purely descriptive sphere, 

 but in the more speculative field as well. 



