of Leibniz without penetrating into his spirit, and that consequently they misrepresented him on every important point. He, Kant, on the other hand, making no claim to use the terminology of Leibniz, was his true continuator, since he had only changed the doctrine of the latter so as to make it conform to the true intent of Leibniz, by removing its self-contradictions. He closes: “‘The Critique of Pure Reason’ may be regarded as the real apology for Leibniz, even against his own professed followers.”
Kant, in particular, names three points in which he is the true follower of Leibniz. The professed disciples of the latter insisted that the law of sufficient reason was an objective law, a law of nature. But, says Kant, it is so notorious, so self-evident, that no one can make a new discovery through this principle, that Leibniz can have meant it only as subjective. “For what does it mean to say that over and above the principle of contradiction another principle must be employed? It means this: that, according to the principle of contradiction, only that can be known which is already contained in the notion of the object; if anything more is to be known, it must be sought through the use of a special principle, distinct from that of contradiction. Since this last kind of knowledge is that of synthetic principles, Leibniz means just this: besides the principle of contradiction, or that of analytic judgments, there must be another, that of sufficient reason, for synthetic judgments. He thus pointed out, in a new and remarkable manner, that certain investigations in metaphysics were still to be made.” In other words, Kant, by his distinction of analytic and synthetic judgments, with their respective principles and spheres, carried out the idea of Leibniz regarding the principles of contradiction and sufficient reason.
The second point concerns the relation of monads to material bodies. Eberhard, like the other professed Leibnizians, interpreted Leibniz as saying that corporeal bodies, as composite, are actually made up out of monads, as simple. Kant, on the other hand, saw clearly that Leibniz was not thinking of a relation of composition, but of condition. “He did not mean the material world, but the substrate, the intellectual world which lies in the idea of reason, and in which everything must be thought as consisting of simple substances.” Eberhard’s process, he says, is to begin with sense-phenomena, to find a simple element as a part of the sense-perceptions, and then to present this simple element as if it were spiritual and equivalent to the monad of Leibniz. Kant claims to follow the thought of Leibniz in regarding the simple not as an element in the sensuous, but as something super-sensuous, the ground of the sensuous. Leibniz’s mistake was that, not having worked out clearly the respective limits of the principles of identity and of sufficient reason, he supposed that we had a direct intellectual intuition of this super-sensuous, when in reality it is unknowable.
The third group of statements concerns the principle of pre-established harmony. “Is it possible,” asks Kant, “that Leibniz meant by this doctrine to assert the mere coincidence of two substances wholly independent of each other by nature, and incapable through their own force of being brought into community?” And his answer is that what Leibniz really implied was not a harmony between independent things, but a harmony between modes of knowing, between sense on the one hand and understanding on the other. The “Critique of Pure Reason” carried the discussion farther by pointing out its grounds; namely, that, without the unity of sense and understanding, no experience would be possible. Why there should be this harmony, why we should have experience, this question it is impossible to answer, says Kant,—adding that Leibniz confessed as much when he called it a “pre-established” harmony, thus not explaining it, but only referring it to a highest cause. That Leibniz really means a harmony within intelligence, not a harmony of things by themselves, is made more clear, according to Kant, from the fact that it is applied also to the relation between the kingdom of nature and of grace, of final and of efficient causes. Here the harmony is clearly not between two independently existing external things, but between what flows from our notions of nature (Naturbegriffe) and of freedom (Freiheitsbegriffe); that is, between two distinct powers and principles within us,—an agreement which can be explained only through the idea of an intelligent cause of the world.
If we review these points in succession, the influence of Leibniz upon Kant becomes more marked. As to the first one, it is well known that Kant’s philosophy is based upon, and revolves within, the distinction of analytic and synthetic judgments; and this distinction Kant clearly refers to the Leibnizian distinction between the principles of contradiction and of sufficient reason, or of identity and differentiation. It is not meant that Kant came to this thought through the definitions of Leibniz; on the contrary, Kant himself refers it to Hume’s distinction between matters of fact and relations of ideas. But when Kant had once generalized the thought of Hume, it fell at once, as into ready prepared moulds, into the categories of Leibniz. He never escapes from the Leibnizian distinction. In his working of it out consists his greatness as the founder of modern thought; from his acceptance of it as ultimate result his contradictions. That is to say, Kant did not merely receive the vague idea of sufficient reason: he so connected it with what he learned from Hume that he transformed it into the idea of synthesis, and proceeded to work out the conception of synthesis in the various notions of the understanding, or categories, as applicable to the material of sense. What Leibniz bequeathed him was the undefined idea that knowledge of matters of fact rests upon the principle of sufficient reason. What Kant did with this inheritance was to identify the wholly vague idea of sufficient reason with the notion that every fact of experience rests upon necessary synthetic connection,—that is, connection according to notions of understanding with other facts,—and to determine, so far as he could, the various forms of synthesis, or of sufficient reason. With Leibniz the principle remained essentially infertile, because it was the mere notion of the ultimate reference of experience to understanding. In the hands of Kant, it became the instrument of revolutionizing philosophy, because Kant showed the articulate members of understanding by which experience is constituted, and described them in the act of constituting.
So much for his working out of the thought. But on the other hand, Kant never transcended the absoluteness of the distinction between the principles of synthesis and analysis, of sufficient reason and contradiction. The result was that he regarded the synthetic principle as the principle only of our knowledge, while perfect knowledge he still considered to follow the law of identity, of mere analysis. He worked out the factor of negation, of differentiation, contained in the notion of synthesis, but limited it to synthesis upon material of sense, presupposing that there is another kind of knowledge, not limited to sense, not depending upon the synthetic principle, but resting upon the principle of contradiction, or analysis, and that this kind is the type, the norm, of the only perfect knowledge. In other words, while admitting the synthetic principle of differentiation as a necessary element within our knowledge, he held that on account of this element our knowledge is limited to the phenomenal realm. Leibniz’s error was in supposing that the pure principles of the logical understanding, resting on contradiction, could give us knowledge of the noumenal world; his truth was in supposing that only by such principles could they be known. Thus, in substance, Kant. Like Leibniz, in short, he failed to transcend the absoluteness of the value of the scholastic method; but he so worked out another and synthetic method,—the development of the idea of sufficient reason,—that he made it necessary for his successors to transcend it.
The second point concerns the relations of the sensuous and the super-sensuous. Here, besides setting right the ordinary misconception of Leibniz, Kant did nothing but render him consistent with himself. Leibniz attempted to prove the existence of God, as we have seen, by the principles both of sufficient reason and contradiction. Kant denies the validity of the proof by either method. God is the sufficient cause, or reason, of the contingent sense world. But since Leibniz admits that this contingent world may, after all, be but a dream, how shall we rise from it to the notion of God? It is not our dreams that demonstrate to us the existence of reality. Or, again, sense-knowledge is confused knowledge. How shall this knowledge, by hypothesis imperfect, guarantee to us the existence of a perfect being? On the other hand, since the synthetic principle, or that of sufficient reason, is necessary to give us knowledge of matters of fact, the principle of contradiction, while it may give us a consistent and even necessary notion of a supreme being, cannot give this notion reality.
