answer that an infinity of monads multiplies his existence so far as possible, may hold indeed of other spirits, who mirror him and live in one divine society, but is utterly inapplicable to those which fail to image him. Their existence, as material, is merely privative; it is merely the absence of the activity found in conscious spirit. How can this deprivation, this limitation, increase in any way the harmony and perfection of the universe? Leibniz’s theory of the negative, in fine, compels him to put nature and spirit on the same level, as differing only in degree. This, so far from giving nature a reality, results in its being swallowed up in spirit, not as necessarily distinct from it and yet one with it, but as absorbed in it, since the apparent difference is only privative. Nor does the theory insure the reality of spirit. This, since one in kind with matter, is swallowed up along with it in the one substance, which is positive and self-identical,—in effect, the Deus sive Natura of Spinoza.
We have to see that this contradiction on the side of existence has its correlate on the side of knowledge, and our examination of this fundamental deficiency in Leibniz is ended. Sensation is on the side of intelligence what matter is on the side of reality. It is confused knowledge, as matter is imperfect activity or reality. Knowledge is perfect only when it is seen to be necessary, and by “necessary” is meant that whose opposite is impossible, or involves contradiction. In spite, therefore, of Leibniz’s thorough conviction that “matters of fact”—the subject-matter of physical science—are not arbitrary, he is yet obliged finally to agree with Locke that there is no certainty to be found in such knowledge, either as a whole or in any of its details. The element of sensation, of confused knowledge, cannot be eliminated. Hence it must always be open to any one to object that it is only on account of this imperfect factor of our knowledge that there appears to be a physical world at all, that the external world is an illusion produced by our sensations. And Leibniz himself, while claiming that the world of fact, as opposed to the realm of relations, possesses practical reality, is obliged to admit that metaphysically it may be only an orderly dream. The fact is that Leibniz unconsciously moves in the same circle, with relation to sensation and the material world, that confines Spinoza with regard to imagination and particular multiple existences. Spinoza explains the latter from that imperfection of our intelligence which leads us to imagine rather than to think. But he accounts for the existence of imagination, when he comes to treat that, as due to the plurality of particular things. So Leibniz, when an account of the existence of matter is demanded of him, refers to confused knowledge as its source, while in turn he explains the latter, or sensation, from the material element which sets bounds to the activity of spirit. Leibniz seems indeed, to advance upon Spinoza in admitting the reality of the negative factor in differentiating the purely self-identical, but he gives up what he has thus gained by interpreting the negation as passivity, or mere deprivation.
To sum up, it may be doubted whether we have more to learn from Leibniz’s successes or from his failures. Leibniz’s positive significance for us is in his clear recognition of the problems of modern philosophy, and in his perception of the isolated elements of their solution. His negative significance is in his clinging to a method which allowed him only to juxtapose these elements without forming of them a true synthesis. There are a number of sides from which we may state Leibniz’s realization of the problem. Perhaps that which distinguishes Leibniz most clearly from Locke is their respective treatments of the relation of the physical to the spiritual, or, as the question presented itself mainly to them, of the “natural” to the “supernatural.” To Locke the supernatural was strictly miraculous; it was, from our standpoint, mere power, or will. It might indeed be rational, but this reason was incapable of being apprehended by us. Its distinction from the finite was so great that it could be conceived only as something preceding and succeeding the finite in time, and meanwhile as intercalating itself arbitrarily here and there into the finite; as, for example, in the relation of soul and body, in the production of sensation, etc. In a word, Locke thought that the ends of philosophy, and with it of religion and morals, could be attained only by a complete separation of the “natural” and the “supernatural.” Leibniz, on the other hand, conceived the aim of philosophy to be the demonstration of their harmony. This is evidenced by his treatment of the relations of the infinite and finite, of matter and spirit, of mechanical and final causation. And he found the sought-for harmony in the fact that the spiritual is the reason, purpose, and function of the natural. The oft-quoted words of Lotze express the thought of Leibniz: “The mechanical is unbounded in range, but is subordinate in value.” We cannot find some things that occur physically, and others that occur supernaturally; everything that occurs has its sufficient mechanical antecedents, but all that occurs has its significance, its purpose, in something that does not occur, but that eternally is—Reason. The mechanical and the spiritual are not realms which here and there come into outward contact. They are related as the conditioned and the conditioning. That, and not the idea of an artificial modus vivendi, is the true meaning of the pre-established harmony.
In other words, Leibniz’s great significance for us is the fact that, although he accepted in good faith, and indeed as himself a master in its methods, the results and principles of physical science, he remained a teleological idealist of the type of Aristotle. But I have not used the right words. It was not in spite of his acceptance of the scientific view of the world that he retained his faith in the primacy of purpose and reason. On the contrary, he was an idealist because of his science, because only by the idea of an all-conditioning spiritual activity could he account for and make valid scientific conceptions; he was a teleologist, because natural processes, with their summing up in the notion of causality, were meaningless except as manifesting an immanent purpose.
There are other more technical ways of stating the bearing of Leibniz’s work. We may say that he realized that the problem of philosophy consisted in giving due value to the notions of individuality and universality, of identity and difference, or of the real and the ideal. In developing these ideas, however, we should only be repeating what has already been said, and so we may leave the matter here. On the negative side we need only recall what was said a few pages back regarding the incompatibility of Leibniz’s method—the scholastic formal logic—with the content of his philosophy. The attempt to find a formal criterion of truth was hopeless; it was worse than fruitless, for it led to such an interpretation of concrete truths as to deprive them of their significance and as to land Leibniz in involved contradictions.
To write a complete account of the influence of Leibniz’s philosophy would be too large a task for these pages. If we were to include under this head all the ramifications of thought to which Leibniz stimulated, directly and indirectly, either by stating truths which some one worked out or by stating errors which incited some one to new points of view, we should have to sketch German philosophy since his time,—and not only the professional philosophy, but those wide aspects of thought which were reflected in Herder, Lessing, and Goethe. It is enough to consider him as the forerunner of Kant. It has become so customary to represent Kant as working wholly on the problem which Hume presented, that his great indebtedness to Leibniz is overlooked. Because Hume aroused Kant from his dogmatic slumbers, it is supposed that Kant threw off the entire influence of the Leibnizian thought as vain dreams of his sleep. Such a representation is one-sided. It is truer to state that Hume challenged Kant to discover the method by which he could justify the results of Leibniz. In this process, the results, no doubt, took on a new form: results are always relative to method; but Kant never lost sight of the results. In the main, he accepted the larger features of the Leibnizian conclusions, and, taught by Hume of the insufficiency of the method that Leibniz followed, searched for a method which should guarantee them.
This aspect of Kant appears more fully in his lesser and somewhat controversial writings than in his classic works: and this, no doubt, is one reason that his indebtedness is so often overlooked. His close relation to Leibniz appears most definitely in his brochure entitled “Concerning a Discovery which renders Unnecessary all Critique of Pure Reason.” A Wolffian, Eberhard by name, had “made the discovery” (to use Kant’s words) “that the Leibnizian philosophy contained a critique of reason just as well as the modern, and accordingly contained everything that is true in the latter, and much else in addition.” In his reply to this writing, Kant takes the position that those who
