134 INTRODUCTION 



philosophy. All truth is innate, virtually if not actually. 

 But there are two kinds of truth. Eternal and necessary 

 truth has its ground in the principle of contradiction. 

 It is either self-evident or the result of strict demonstra- 

 tion from the self-evident. l Our mind is the source of 

 necessary truths, and however many particular experiences 

 we may have of a universal truth, we cannot assure our- 

 selves of it for ever by induction without knowing its 

 necessity through reason. . . . The senses may suggest, 

 support, and confirm these truths, but cannot demon- 

 strate their infallible and perpetual certainty 1 .' On the 

 other hand, truth of fact or contingent truth, while 

 equally innate, is not demonstrable through the principle 

 of contradiction, but through that of sufficient reason 2 . 

 It is obtained by induction rather than demonstration. 

 It is truth of experience, or perception which we cannot 

 analyze into perfect distinctness and self -evidence, because 

 of the infinite complexity of its relations to the system of 



1 Nouveaitx Essais, bk. i. ch. i, 5 (E. 209 b ; G. v. 76, 77). 



2 Thus Leibniz rejects the view of Locke that our real know- 

 ledge, as distinct from merely probable knowledge, 'extends as 

 far as the present testimony of our senses, employed about par- 

 ticular objects that do then affect them, and no farther.' (Essay, 

 bk. iv. ch. n, 9 ; Eraser's ed., vol. ii. p. 332.) Cf. the corresponding 

 passage in the Nouveaux Essais (E. 378 b ; G. v. 426) : 'Yet I think 

 that we might extend the names of knowledge and certainty to things 

 other than actual sensations, for clearness and plainness [evidence] 

 extend further, and I regard them as a kind of certainty : and it 

 would without doubt be an absurdity seriously to doubt whether 

 there are men in the world, when we do not see any. To doubt 

 seriously is to doubt practically, and we might take certainty as 

 a knowledge of truth which we cannot doubt practically without 

 madness ; and sometimes we take certainty in a still more general 

 sense and apply it to cases in which we cannot doubt without 

 deserving to be greatly blamed. But evidence would be a luminous 

 certainty, that is to say, a certainty such that, because of the 

 connexion we see between the ideas, we have no doubt whatever. 

 According to this definition of certainty, we are certain that 

 Constantinople is in the world, that Constantine, Alexander the 

 Great, and Julius Caesar have existed. It is true that some 

 peasant of the Ardennes might justly doubt these things, from 

 lack of information ; but a man of letters and of the world could 

 not do so, without great mental derangement.' Cf. also Locke's 

 Essay, bk. ii. ch. ai, 75 (Eraser's ed., vol. i. p. 373). 



