ESTIMATE OF LEIBNIZ S PHILOSOPHY 173 



presuppositions. It ensures order and necessary con- 

 nexion in thought, but it is inadequate to reality. It 

 gives the logical ground of things (logisclie G-rund) but 

 not the ground of their reality (Eeal-grund) \ Thus the 

 principle of contradiction is insufficient when treated as 

 the ultimate principle of metaphysics. Kant develops 

 this position in connexion with the problem of proving 

 the existence of God. He rejects, as a begging of the 

 question, the Cartesian demonstration which maintains 

 that existence is necessarily involved in the perfection of 

 the most perfect Being. Existence, Kant says, cannot be 

 a predicate. That is to say, you cannot take out of any 

 subject more than is contained in it ; the principle of 

 contradiction will never entitle you to pass from any 

 mere idea to the reality of that idea. Pure thought, 

 determined by the principle of contradiction, always 

 presupposes something 'given,' and thus reality must 

 ultimately lie outside of pure thought. Thus, for example, 

 the real cause of anything is always more than a mere 

 reason : a causal connexion is not a merely logical con- 

 nexion. It is this line of thinking that leads Kant to 

 emphasize the distinction between logical understanding 

 and empirical sense, and to lay stress on l experience ' (un- 

 rationalized and unexplained) as the ground of reality, 

 in a way that recalls the position of Locke. Thus, while 

 admitting the certainty of mathematics, Kant protests 

 against the use of a purely mathematical method in deal- 

 ing with metaphysics or with the theory of knowledge, 

 on the ground that such a method is ' merely synthetic, ' 

 that is to say, on the ground that it does not analyze 

 actual experience but deduces from (or builds upon) arbi- 



1 Cf. Der einzig mogliche Beweisgrund zu einer Demonstration des 

 Daseins Gottes (1763) (Rosenkranz, i. 161 ; Hartenstein, vi. n). Kant 

 makes advances towards this position in the Essay on Die falsche 

 Spitsfindigkeit der vier syllogistischen Figuren (1762) (Rosenkranz, i. 55 ; 

 Hartenstein, i. i), and in the Versuch den Begriff der negatiren Grossen 

 in die Weltweisheit einzufuhren (1763) (Rosenkranz, i. 113; Harten- 

 stein, i. 19). 



