AS A MENTAL OPERATION 19 



Philosophiae Naturalis Principia Mathematica. So far 

 Newton justified the deductive logic of Aristotle, and so 

 far he transcended the inductive logic of Bacon. He found 

 that induction is not the sole avenue to all the uniformi- 

 ties of Nature, because from inductive principles deduc- 

 tion goes on to derivative uniformities. At the same 

 time, Newton's example did not prove Aristotle wholly 

 right, or Bacon wholly wrong. His method goes beyond 

 both. Having further deduced that the satellites of 

 planets and the moon in relation to the earth revolve 

 by the same centripetal force of gravitation, he returned 

 from deduction to induction. Using earthly bodies, 

 moon, planets, and satellites as great groups of instances, 

 he induced the universal law of gravitation, and that all 

 the particles of ponderable matter gravitate to one 

 another by the same law. This is exactly a Baconian 

 induction of a uniform principle from heterogeneous 

 instances, from instances however gained not by ex- 

 perience, but by deduction. But, in fact, the scientific 

 method of Newton's Principia, viewed as a whole, is 

 neither the deductive Aristotelian, nor the inductive 

 Baconian, but both : it is the interaction of induction 

 and deduction in a mixed method. 



The method of analytical deduction from facts to 

 causes, and the method of first describing facts and then 

 explaining them by their causes 1 , had been anticipated 

 by Aristotle, who, however, somewhat lost the fruit of 

 his wisdom by too great an emphasis on synthetic mathe- 

 matical demonstration. It remained for Mill in our times 

 to revive the explanatory method, which consists mainly 

 of facts and causes, and the explanation of the former by 

 the latter. Mill, however, did not understand analysis, 



1 See De Parlibus Am'mah'um, Book I. 

 C 2 



