There are few instances of philosophers that have had such a deep influence as Aristotle, or of cosmologists whose theories have endured as long as Ptolemy's. Aristotle's influence is enormous ranging form the sciences to logic. Many of his ideas have endured the test of the centuries. His cosmology, based on a geocentric system, is not one of them. In the words of W. Durant:
|"His curious mind is interested, to begin with, in the process and techniques of reasoning; and so acutely does he analyze these that his Organon, or Instrument-the name given after his death to his logical treatises-became the textbook of logic for two thousand years. He longs to think clearly, though he seldom, in extant works, succeeds; he spends half his time defining his terms, and then he feels that he has solved the problem."|
It must me noted, however, that he forcefully argued for the sphericity of the Earth based on data: he noted that only a spherical Earth can account for the shadow seen on the Moon during a lunar eclipse
Ptolemy enlarged Aristotle's ideas creating a very involved model of the solar system which endured until the Copernican revolution of the middle 16th century. When comparing the Ptolemaic system with the Copernican heliocentric system Ockham's razor (Sect. 1.2.5) instantly tells us to consider the latter first: it provide a much simpler explanation (and, as it turns out, a much better one) that the former.