The Science of Conjecture: Evidence and Probability Before Pascal

by James Franklin

Kepler and Galileo share the same project, the mathematization of science, support the same unorthodox thesis, heliocentrism, and often propose the same arguments. They both interpret astronomy realistically—Kepler was the first to call attention to the fact that the preface to De Revolutionibus was not written by Copernicus, and Galileo rejected the suggestion that he regard Copernicanism as fictitious to reconcile it with theology. They distinguish between probable and demonstrative arguments for that thesis in the same way. Their genius is equally exceptional. It has therefore often been wondered why they took so little notice of each other; Galileo, for example, never took seriously Kepler’s principal discovery, that the planetary orbits are elliptical. Of course, geniuses are very busy people and often have no time to read one another’s works. But in this case, their styles of thinking and writing show a fundamental incompatibility sufficient to make them almost incomprehensible to each other.