OF KNOWLEDGE. 



327 



tliinkers during the nineteenth century. But the fact 

 which must have troubled all those thinkers who 

 worked at the unification of thought and the criteria of 

 certainty — viz., the existence of the actual knowledge of 

 science on the one side and the spiritual knowledge of 

 faith on the other — was not sufficiently explained or 

 traced to its psychological sources either by Descartes 

 or by Spinoza. Leibniz works out the theory of know- 

 ledge in opposition to the Cartesian view as well as to 

 that of Locke. It is not correct, according to his view, 

 that all true knowledge is limited to that which can be 

 clearly defined, as the Cartesians maintained, nor is the 

 soul originally a tahula rasa as Locke and the empiricists 

 maintained. Only a portion of our soul is at any time 

 fully illuminated, only a portion of our thoughts arrive 

 at the clarity of discursive knowledge.^ Behind and 



^ The two most important ideas 

 wiiich Leibniz has the merit of 

 introducing into the theory of 

 knowledge, and for which he coined 

 two distinct terms, are the doctrine 

 of the " petites perceptions " and 

 that of "apperception," as distin- 

 guished from "perception." Both 

 these ideas, which have become so 

 fruitful in recent philosophy, are 

 contained in Leibniz's later, mostly 

 posthumously published, works and 

 correspondence. Originally mainly 

 interested in a development or 

 correction of the Cartesian system 

 as a comprehensive reasoned creed, 

 he had devoted himself to the 

 study of the two most prominent 

 problems that Descartes had be- 

 queathed to his successors. Those 

 were, first, the problem of method ; 

 secondly, the central metaphysical 

 conception of the ultimate reality 

 — the notion of substance. His 

 important psychological, and his 



still more important epistemo- 

 logical, discussions seem to have 

 come to the fore much later, 

 notably through his acquaintance 

 with the writings of Locke and 

 Newton ; the former suggested the 

 'Nouveaux Essais,' the latter led 

 to the correspondence with Clarke. 

 Leibniz's earlier labours were in 

 the direction of the development 

 of the mathematical methods, and 

 resulted inter alia in his invention 

 of the calculus, but also in his 

 fruitless attempts to import greater 

 precision into philosophical reason- 

 ing by the invention of a general 

 combinatorial method or logical 

 calculus which should not only 

 prove, but also lead to the dis- 

 covery of new truths. " From 

 early youth he had the hope to 

 find such an art, and it is remark- 

 able that a man of his mental cast, 

 and with his appreciation of the 

 meaning of individuality, should 



