BEGINNINGS OF MODERN MATHEMATICAL SCIENCE 275 



If this discourse seems too long to be read all at once, it can be 

 divided into six parts. In the first will be found various considera- 

 tions concerning the sciences ; in the second, the chief rules of the 

 method which the author has sought; in the third, some of those 

 of ethics which he has deduced by this method ; in the fourth, the 

 reasons by which he proves the existence of God and of the human 

 soul, which are the foundations of his metaphysics ; in the fifth, the 

 order of questions of physics which he has sought, and particularly 

 the explanation of the movement of the heart and of some other 

 difficulties which belong to medicine ; also the difference which exists 

 between our soul and that of the beasts; and in the last, what 

 things he believes necessary in order to go farther in the investiga- 

 tion of nature than has been done, and what reasons have made 

 him write. 



Good sense is the most widely distributed commodity in the 

 world, for every one thinks himself so well supplied with it that even 

 those who are hardest to satisfy in every other respect are not accus- 

 tomed to desire more of it than they have. In this it is not prob- 

 able that all men are mistaken, but rather this testifies that the power 

 of good judgment and of discriminating between the true and the false, 

 which is properly what one calls good-sense or reason, is naturally 

 equal in all men ; and thus that the diversity of our opinions is not 

 due to the fact that some are more reasonable than others, but only 

 that we conduct our thought along different channels, and do not 

 consider the same things. For it is not enough to have a good mind, 

 but the principal thing is to apply it well. The greatest souls are 

 capable of the greatest vices as well as of the greatest virtues: and 

 those who only progress very slowly can advance much more, if 

 they follow always the straight road than do those who run, depart- 

 ing from it. 



His four cardinal precepts were : 



Never to receive anything for true which he did not recognize to be 

 evidently so; that is, to avoid carefully precipitancy and prejudg- 

 ment. Second, to divide each of the difficulties which he should 

 examine into as many pieces as possible. Third, to conduct his 

 thoughts in order, beginning with the simplest objects. The last, 

 to make everywhere enumerations so complete and reviews so general 

 that he should be assured of omitting nothing. 



