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In the exposition now completed we have in general taken for granted the truth and coherency of Leibniz’s fundamental ideas, and have contented ourselves with an account of the principles and notions that flow from these ideas. The time has come for retracing our steps, and for inquiring whether the assumed premises can be thus unquestioningly adopted. This final chapter, therefore, we shall devote to criticism of the basis of Leibniz’s philosophy, not attempting to test it by a comparison with other systems, but by inquiring into its internal coherency, and by a brief account of the ways in which his successors, or at least one of them, endeavored to make right the points in which he appeared to fail.

The fundamental contradiction in Leibniz is to be found, I believe, between the method which he adopted—without inquiry into its validity and scope—and the subject-matter, or perhaps better the attitude, to which he attempted to apply this method; between, that is to say, the scholastic formal logic on the one hand and the idea of inter-relation derived from the development of scientific thought, on the other. Leibniz never thought of investigating the formal logic bequeathed by scholasticism, with a view to determining its adequacy as philosophic method. He adopted, as we have seen, the principles of identity and contradiction as sole principles of the only perfect knowledge. The type of knowledge is that which can be reduced to a series of identical propositions, whose opposite is seen to be impossible, because self-contradictory. Only knowledge in this form can be said to be demonstrative and necessary. As against Locke he justified the syllogistic method of the schoolmen as the typical method of all rational truth.

On the other hand, Leibniz, as we saw in the earlier chapters, had learned positively from the growth of science, negatively from the failures of Descartes and Spinoza, to look upon the universe as a unity of inter-related members,—as an organic unity, not a mere self-identical oneness. Failing to see the cause of the failures of Descartes and Spinoza in precisely their adoption of the logic of identity and contradiction as ultimate, he attempted to reconcile this method with the conception of organic activity. The result is constant conflict between the method and content of his philosophy, between its letter and its spirit. The contradiction is a twofold one. The unity of the content of his philosophy, the conception of organism or harmony, is a unity which essentially involves difference. The unity of his method is a formal identity which excludes it. The unity, whose discovery constitutes Leibniz’s great glory as a philosopher, is a unity of activity, a dynamic process. The unity of formal logic is exclusive of any mediation or process, and is essentially rigid and lifeless. The result is that Leibniz is constantly wavering (in logical result, not of course in spirit) between two opposed errors, one of which is, in reality, not different from Spinozism, in that it regards all distinction as only phenomenal and unreal, while the other is akin to atomism, in that attempting to avoid the doctrine of the all-inclusive one, it does so only by supposing a multitude of unrelated units, termed monads. And thus the harmony, which in Leibniz’s intention is the very content of reality, comes to be, in effect, an external arrangement between the one and the many, the unity and the distinction, in themselves incapable of real relations. Such were the results of Leibniz’s failure, in Kantian language, to criticise his categories, in Hegelian language, to develop a logic,—the results of his assuming, without examination, the validity of formal logic as a method of truth.

So thoroughly is Leibniz imbued with the belief in its validity, that the very conception, that of sufficient reason, which should have been the means of saving him from his contradictions, is used in such a way as to plunge him deeper into them. The principle of sufficient reason may indeed be used as purely formal and external,—as equivalent to the notion that everything, no matter what, has some explanation. Thus employed, it simply declares that everything has a reason, without in the least determining the what of that reason,—its content. This is what we mean by calling it formal. But this is not the way in which Leibniz conceives of it. According to him, it is not a principle of the external connection of one finite, or phenomenal, fact with another. It is a principle in the light of which the whole phenomenal world is to be viewed, declaring that its ground and meaning are to be found in reason, in self-conscious intelligence. As we have seen, it is equivalent, in Leibniz’s case, to the notion that we have no complete nor necessary knowledge of the world of scientific fact until we have referred it to a conditioning “Supreme Spirit.”

Looked at in this way, we see that the unity which Leibniz is positively employing is an organic unity, a unity of intelligence involving organic reference to the known world. But such a conception of sufficient reason leaves no place for the final validity of identity and non-contradiction; and therefore Leibniz, when dealing with his method, and not, as in the passages referred to, with his subject-matter, cannot leave the matter thus. To do so indeed would have involved a complete reconstruction of his philosophy, necessitating a derivation of all the categories employed from intelligence itself (that is, from the sufficient or conditioning reason). But the bondage to scholastic method is so great that Leibniz can see no way but to measure intelligence by the ready-made principle of identity, and thus virtually (though not in purpose) to explain away the very principle of sufficient reason. In Leibniz’s words: “Contingent truths require an infinite analysis which only God can carry out. Whence by him alone are they known a priori and demonstratively. For although the reason can always be found for some occurring state in a prior state, this reason again requires a reason, and we never arrive in the series to the ultimate reason. But this progressus ad infinitum takes (in us) the place of a sufficient reason, which can be found only outside the series in God, on whom all its members, prior and posterior depend, rather than upon one another. Whatever truth, therefore, is incapable of analysis, and cannot be demonstrated from its own reasons, but has its ultimate reason and certainty only from the divine mind, is not necessary. Everything that we call truths of fact come under this head, and this is the root of their contingency.”

The sentences before the one italicized repeat what we have learned before, and seem to convey the idea that the phenomenal world is that which does not account for itself, because not itself a self-determining reason, and which gets its ultimate explanation and ground in a self-sufficient reason,—God. But notice the turn given to the thought with the word “therefore.” Therefore all truth incapable of analysis,—that is, of reduction to identical propositions, whose opposite is impossible because self-contradictory,—all truth whose meaning depends upon not its bare identity, but upon its relation to the very content of all intelligence, is not necessary, but contingent. Leibniz here distinctly opposes identical truths as necessary, to truth connected with reason as contingent. Synthetic reference to the very structure of intelligence is thus made, not the ground of truth, but a blot upon its completeness and necessity. Perfect truth, it is implied in the argument, is self-identical, known by mere analysis of itself, and needs no reference to an organism of reason. The reference, therefore, to a principle of sufficient reason is simply a concession to the fragmentary and imperfect condition of all knowledge. Truth in itself is self-identical; but appearing to us only confusedly, we employ the idea of sufficient reason as a makeshift, by which we refer, in a mass, all that we cannot thus reduce to identical propositions, to an intelligence, or to a Deus ex machina which can so reduce it. This is the lame and impotent conclusion.

Leibniz’s fundamental meaning is, no doubt, a correct one. He means that contingency of fact is not real, but apparent; that it exists only because of our inability to penetrate the reason which would enable us completely to account for the facts under consideration. He means that if we could understand, sub specie aeternitatis, from the standpoint of universal intelligence, we should see every fact as necessary, as resulting from an intrinsic reason. But so thoroughly is he fettered by the scholastic method—that is, the method of formal logic—that he can conceive of this immanent and intrinsic reason which makes every fact a truth—that is, self-evident in its necessity—only as an analytic, self-contained identity. And herein lies his contradiction: his method obliges him to conceive of ultimate intelligence as purely formal, simply as that which does not contradict itself, while the attitude of his thought and its concrete subject-matter compel him to think of intelligence as possessing a content, as the organic unity of a system of relations.

From this contradiction flow the other contradictions of Leibniz, which we are now prepared to examine in more detail. For his ideas are so much greater than his method that in almost every point there seems to be contradiction. His ideas per se mean one thing, and his ideas as interpreted by his method another. Take his doctrine of individuality, for instance. To some it has appeared that the great defect of the Leibnizian philosophy is its individualism. Such conceive him simply to have carried out in his monadism the doctrine of the individual isolated from the universe to its logical conclusions, and thereby to have rendered it absurd. In a certain sense, the charge is true. The monad, according to the oft-repeated statement, has no intercourse with the rest of the universe. It really excludes all else. It acts as if nothing but itself and God were in existence. That is to say, the monad, being the self-identical, must shut out all intrinsic or real relations with other substances. Such relations would involve a differentiating principle for which Leibniz’s logic has no place. Each monad is, therefore, an isolated universe. But such a result has no value for Leibniz. He endeavors to correct it by the thought that each monad ideally includes the whole universe by mirroring it. And then to reconcile the real exclusion and the ideal inclusion, he falls back on a Deus ex machina who arranges a harmony between them, foreign to the intrinsic nature of each. Leibniz’s individualism, it is claimed, thus makes of his philosophy a synthesis, or rather a juxtaposition, of mutually contradictory positions, each of which appears true only as long as we do not attempt to think it together with the other.

There is, no doubt, truth in this representation. But a more significant way of stating the matter is, I think, that Leibniz’s defect is not in his individualism, but in the defect of his conception of the individual. His individualism is more apparent than real. It is a negative principle, and negative in the sense of privative. The individuality of the monad is due to its incompleteness, to its imperfections. It is really matter which makes monads mutually impenetrable or exclusive; it is matter which distinguishes them from God, and thus from one another. Without the material element they would be lost in an undistinguished identity with God, the supreme substance. But matter, it must be remembered, is passivity; and since activity is reality, or substance, matter is unsubstantial and unreal. The same results from a consideration of knowledge. Matter is always correlative to confused ideas. With the clearing up of knowledge, with making it rational, matter must disappear, so that to God, who is wholly reason, it must entirely vanish. But this view varies only in words from that of Spinoza, to whom it is the imagination, as distinguished from the intellect, that is the source of particular and finite objects.

It is perhaps in his Theodicée, in the treatment of the problem of evil, that his implicit Spinozism, or denial of individuality, comes out most clearly. That evil is negative, or privative, and consists in the finitude of the creature, is the result of the discussion. What is this except to assert the unreality, the merely privative character, of the finite, and to resolve all into God? To take one instance out of many: he compares inertia to the original limitation of creatures, and says that as inertia is the obstacle to the complete mobility of bodies, so privation, or lack, constitutes the essence of the imperfection, or evil, of creatures. His metaphor is of boats in the current of a river, where the heavier one goes more slowly, owing to inertia. The force of the current, which is the same to all, and which is positive, suffering no diminution, is comparable to the activity of God, which also is perfect and positive. As the current is the positive source of all the movements of the bodies, and is in no way responsible for the retardation of some boats, so God is the source only of activities,—the perfections of his creatures. “As the inertia of the boat is the cause of its slowness, so the limitations of its receptivity are the cause of the defects found in the action of creatures.” Individuality is thus reduced to mere limitation; and the unlimited, the real which includes all reality, is God. We are thus placed in a double difficulty. This notion of an all-inclusive one contradicts the reality of mutually exclusive monads; and we have besides the characteristic difficulty of Spinoza,—how, on the basis of this unlimited, self-identical substance, to account for even the appearance of finitude, plurality and individuality.

Leibniz’s fundamental defect may thus be said to be that, while he realized, as no one before him had done, the importance of the conception of the negative, he was yet unable to grasp the significance of the negative, was led to interpret it as merely privative or defective, and thus, finally, to surrender the very idea. Had not his method, his presupposition regarding analytic identity, bound him so completely in its toils, his clear perception that it was the negative element that differentiated God from the universe, intelligence from matter, might have brought him to a general anticipation not only of Kant, but of Hegel. But instead of transforming his method by this conception of negation, he allowed his assumed (i. e., dogmatic) method to evacuate his conception of its significance. It was Hegel who was really sufficiently in earnest with the idea to read it into the very notion of intelligence as a constituent organic element, not as a mere outward and formal limitation.

We have already referred to the saying of Leibniz that the monad acts as if nothing existed but God and itself. The same idea is sometimes expressed by saying that God alone is the immediate or direct object of the monad. Both expressions mean that, while the monad excludes all other monads, such is not the case in its relation to God, but that it has an organic relation with him. We cannot keep from asking whether there is not another aspect of the contradiction here. How is it possible for the monad so to escape from its isolation that it can have communication with God more than with other substances? Or if it can have communication with God, why cannot it equally bear real relations of community with other monads? And the answer is found in Leibniz’s contradictory conceptions of God. Of these conceptions there are at least three. When Leibniz is emphasizing his monadic theory, with its aspects of individuality and exclusion, God is conceived as the highest monad, as one in the series of monads, differing from the others only in the degree of its activity. He is the “monad of monads”; the most complete, active, and individualized of all. But it is evident that in this sense there can be no more intercourse between God and a monad than there is between one monad and another. Indeed, since God is purus actus without any passivity, it may be said that there is, if possible, less communication in this case than in the others. He is, as Leibniz says, what a monad without matter would be, “a deserter from the general order.” He is the acme of isolation. This, of course, is the extreme development of the “individual” side of Leibniz’s doctrine, resulting in a most pronounced atomism. Leibniz seems dimly conscious of this difficulty, and thus by the side of this notion of God he puts another. According to it, God is the source of all monads. The monads are not created by a choice of the best of all possible worlds, as his official theology teaches, but are the radiations of his divinity. Writing to Bayle, Leibniz expresses himself as follows: “The nature of substance consists in an active force of definite character, from which phenomena proceed in orderly succession. This force was originally received by, and is indeed preserved to, every substance by the creator of all things, from whom all actual forces or perfections emanate by a sort of continual creation.” And in his Monadology he says: All “the created or derived monads are the productions of God, and are born, as it were, by the continual fulgurations of the divinity from instant to instant, bounded by the receptivity of the creature to which it is essential to be limited.” What has become of the doctrine of monads (although the word is retained) it would be difficult to say. There is certainly no individual distinction now between the created monads and God, and it is impossible to see why there should be individual distinctions between the various created monads. They appear to be all alike, as modes of the one comprehensive substance. Here we have the universal, or “identity,” side of Leibniz’s philosophy pushed to its logical outcome,—the doctrine of pantheism.

His third doctrine of God is really a unity of the two previous. It is the doctrine that God is the harmony of the monads,—neither one among them nor one made up of them, but their organic unity. This doctrine is nowhere expressly stated in words (unless it be when he says that “God alone constitutes the relation and community of substances”), but it runs through his whole system. According to this, God is the pre-established harmony. This conception, like that of harmony, may have either a mechanical interpretation (according to which God is the artificial, external point of contact of intelligence and reality, in themselves opposed) or an organic meaning, according to which God is the unity of intelligence and reality. On this interpretation alone does the saying that God is the only immediate object of the monads have sense. It simply states that the apparent dualism between intelligence and its object which is found in the world is overcome in God; that the distinction between them is not the ultimate fact, but exists in and for the sake of a unity which transcends the difference. According to this view, the opposition between ideal inclusion and real exclusion vanishes. God is the harmony of the real and ideal, not a mere arrangement for bringing them to an understanding with one another. Individuality and universality are no longer opposed conceptions, needing a tertium quid to relate them, but are organic factors of reality, and this, at the same time, is intelligence.

But admitting this conception as stating the implicit intention of Leibniz, the relation of monads to one another is wholly different from that which Leibniz gives. And to this point we now come. If in God, the absolute, the real and the ideal are one, it is impossible that in substances, which have their being and significance only in relation to God, or this unity, the real and the ideal should be so wholly separated as Leibniz conceives.

Leibniz’s conception relative to this is, as we have seen, that there is no physical influxus, or commercium, of monads, but ideal consensus. Really each shuts out every other; ideally, or representatively, it includes every other. His positive thought in the matter is that a complete knowledge of any portion of the universe would involve a perfect knowledge of the whole, so organic is the structure of the universe. Each monad sums up the past history of the world, and is big with its future. This is the conception of inter-relation; the conception of all in one, and one as a member, not a part of a whole. It is the conception which Leibniz brought to birth, the conception of the thorough unity of the world. In this notion there is no denial of community of relation; it is rather the culmination of relation. There is no isolation. But according to his presupposed logic, individuality can mean only identity excluding distinction,—identity without intrinsic relation, and, as Leibniz is bound at all hazards to save the notion of individuality, he is obliged to think of this inter-relation as only ideal, as the result of a predetermined tendency given at its creation to the self-identical monad by God. But of course Leibniz does not escape the contradiction between identity and distinction, between individuality and universality, by this means. He only transfers it to another realm. In the relation of the monad to God the diversity of its content, the real or universal element, is harmonized with the identity of its law, its ideal or individual factor. But if these elements do not conflict here, why should they in the relation of the monads to one another? Either there is already an immanent harmony between the individual and universal, and no external arrangement is needed to bring it about, or there is no such harmony, and therefore no relation possible between God and the individual monad. One side of the Leibnizian philosophy renders the other side impossible.

Another consequence of Leibniz’s treatment of the negative as merely limitative is that he can find no distinction, excepting of degree, between nature and spirit. Such a conception is undoubtedly in advance of the Cartesian dualism, which regards them as opposed realms without any relation; but it may be questioned whether it is as adequate a view as that which regards them as distinct realms on account of relation. At all events, it leads to confusion in Leibniz’s treatment of both material objects and self-conscious personalities. In the former case his method of escape is a metaphor,—that objects apparently material are full of souls, or spirits. This may mean that the material is merely material only when considered in implicit abstraction from the intelligence which conditions it, that the material, in truth, is constituted by some of the relations which in their completeness make up intelligence. This at least bears a consistent meaning. But it is not monadism; it is not the doctrine that matter differs from spirit only in degree: it is the doctrine that they differ in kind, as the conditioned from the conditioning. At times, however, Leibniz attempts to carry out his monadism literally, and the result is that he conceives matter as being itself endowed, in some unexplained way, with souls, or since this implies a dualism between matter and soul, of being made up, composed, of souls. But as he is obliged to explain that this composition is not spatial, or physical, but only ideal, this doctrine tends to resolve itself into the former. And thus we end where we began,—with a metaphor.

On the other hand there is a wavering treatment of the nature of spirit. At times it is treated as precisely on a level in kind with the monads that “compose” matter, differing only in the greater degree of its activity. But at other times it is certainly represented as standing on another plane. “The difference between those monads which express the world with consciousness and those which express it unintelligently is as great as the difference between a mirror and one who sees.” If Leibniz means what he seems to imply by these words, it is plainly asserted that only the spiritual being is worthy of being called a monad, or individual, at all, and that material being is simply a dependent manifestation of spirit. Again he says: “Not all entelechies are, like our soul, images of God,—being made as members of a society or state of which he is chief,—but all are images of the universe.” In this distinction between self-conscious beings as images of God and unconscious monads as images of the universe there is again implied a difference of kind. That something is the image of the universe need mean only that it cannot be explained without its relations to the universe. To say that something is the image of God, must mean that it is itself spiritual and self-conscious. God alone is reason and activity. He alone has his reality in himself. Self-conscious beings, since members of a community with him, must participate in this reality in a way different in kind from those things which, at most, are only substances or objects, not subjects.

Nor do the difficulties cease here. If matter be conceived, not as implied in the relations by which reason is realized in constituting the universe, but as itself differing from reason only in degree, it is impossible to account for its existence. Why should a less degree of perfection exist than is necessary? Why should not the perfect activity, God, complete the universe in himself? Leibniz’s 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 claimed to be Leibnizians simply repeated the words 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. Leibniz, while admitting, with regard to all other matters of fact, that the principles of formal logic can give no unconditional knowledge, yet supposes that, with regard to the one unconditional reality, they are amply sufficient. Kant but renders him self-consistent on this point.

It is, however, with regard to the doctrine of pre-established harmony that Kant’s large measure of indebtedness to Leibniz is most apt to be overlooked. Kant’s claim that Leibniz himself meant the doctrine in a subjective sense (that is, of a harmony between powers in our own intelligence) rather than objective (or between things out of relation to intelligence) seems, at first sight, to go far beyond the mark. However, when we recall that to Leibniz the sense world is only the confused side of rational thought, there is more truth in Kant’s saying than appears at this first sight. The harmony is between sense and reason. But it may at least be said without qualification that Kant only translated into subjective terms, terms of intelligence, what appears in Leibniz as objective. This is not the place to go into the details of Kant’s conception of the relation of the material to the psychical, of the body and the soul. We may state, however, in his own words, that “the question is no longer as to the possibility of the association of the soul with other known and foreign substances outside it, but as to the connection of the presentations of inner sense with the modifications of our external sensibility.” It is a question, in short, of the harmony of two modes of our own presentation, not of the harmony of two independent things. And Kant not only thus deals with the fact of harmony, but he admits, as its possible source, just what Leibniz claims to be its actual source; namely, some one underlying reality, which Leibniz calls the monad, but to which Kant gives no name. “I can well suppose,” says Kant, “that the substance to which through external sense extension is attributed, is also the subject of the presentations given to us by its inner sense: thus that which in one respect is called material being would be in another respect thinking being.”

Kant treats similarly the problem of the relations of physical and final causes, of necessity and freedom. Here, as in the case just mentioned, his main problem is to discover their harmony. His solution, again, is in the union, in our intelligence, of the understanding—as the source of the notions which “make nature”—with the ideas of that reason which gives a “categorical imperative.” The cause of the possibility of this harmony between nature and freedom, between the sense world and the rational, he finds in a being, God, whose sole function in the Kantian philosophy may be said to be to “pre-establish” it. I cannot believe that Kant, in postulating the problems of philosophy as the harmony of sense and understanding, of nature and freedom, and in finding this harmony where he did, was not profoundly influenced, consciously as well as unconsciously, by Leibniz. In fact, I do not think that we can understand the nature either of Kant’s immense contributions to modern thought or of his inconsistencies, until we have traced them to their source in the Leibnizian philosophy,—admitting, on the other hand, that we cannot understand why Kant should have found necessary a new way of approach to the results of Leibniz, until we recognize to the full his indebtedness to Hume. It was, indeed, Hume that awoke him to his endeavors, but it was Leibniz who set before him the goal of these endeavors. That the goal should appear somewhat transformed, when approached from a new point of view, was to be expected. But alas! the challenge from Hume did not wholly awaken Kant. He still accepted without question the validity of the scholastic method,—the analytic principle of identity as the type of perfect knowledge,—although denying its sufficiency for human intelligence. Leibniz suggested, and suggested richly, the synthetic, the negative aspect of thought; Kant worked it out as a necessary law of our knowledge; it was left to his successors to work it out as a factor in the law of all knowledge.

It would be a grievous blunder to suppose that this final chapter annihilates the earlier ones; that the failure of Leibniz as to method, though a failure in a fundamental point, cancelled his splendid achievements. Such thoughts as that substance is activity; that its process is measured by its end, its idea; that the universe is an inter-related unit; the thoughts of organism, of continuity, of uniformity of law,—introduced and treated as Leibniz treated them,—are imperishable. They are members of the growing consciousness, on the part of intelligence, of its own nature. There are but three or four names in the history of thought which can be placed by the side of Leibniz’s in respect to the open largeness, the unexhausted fertility, of such thoughts. But it is not enough for intelligence to have great thoughts nor even true thoughts. It is testimony to the sincerity and earnestness of intelligence that it cannot take even such thoughts as those of Leibniz on trust. It must know them; it must have a method adequate to their demonstration. And in a broad sense, the work of Kant and of his successors was the discovery of a method which should justify the objective idealism of Leibniz, and which in its history has more than fulfilled this task.