(2) _The Intellectual Standards differ in the Two Periods._ The Humanistic Period has been well characterized as the time of “the struggle of traditions.” Naturally enough, with the revival of Greek learning the thinkers of the first period of the Renaissance would try to solve the new problems by the standards which they found in antiquity. What did Aristotle, Plato, the Epicureans say in matters of science? What standards did they yield for solving the new problems of the “new universe”? The traditions of antiquity were therefore revived; and the contention was, Which should be taken as a standard? Among all the ancient systems neo-Platonism became the most prominent. It dominated the Humanistic Period because its æsthetic character and its mystical explanations appealed to the susceptible mind of that time. Nevertheless, the sway of neo-Platonism was not absolute. The “struggle of traditions” continued throughout the period, as appears in the schisms of the church and in the literary and philosophical contentions. The Natural Science Period, in its hope of finding a standard to explain the problems of the “new universe,” discovered a new standard within the “new universe” itself. No tradition of antiquity had proved itself adequate to the situation. Nothing could be found in Plato and Aristotle to give a theoretic standard for the new discoveries and inventions. Nature disclosed its own standard within itself. The Natural Science Period said _nature facts must be explained by nature facts_. But the question will naturally be asked, Why did the thinkers of this period, when the theories of antiquity were found to be inadequate, turn to nature rather than elsewhere for an explanation of nature? The answer to this is found in the great successes of the physical astronomers, who had started their investigations at the beginning of the Humanistic Period, and had reached the zenith of their glory at the beginning of the Natural Science Period. The discoveries of Galileo were especially important.