Leibniz's New Essays Concerning the Human Understanding Part 2

The reader, impatient of what may have seemed an over-long introduction, has perhaps been asking when he was to be brought to the subject under consideration,--the relations of Leibniz to Locke. But it has been impossible to come to this question until we had formed for ourselves an outline of the philosophical position of Leibniz. Nowhere in the "Nouveaux Essais" does Leibniz give a connected and detailed exposition of his philosophy, either as to his standpoint, his fundamental principles, or his method.

Some preliminary view of his position is therefore a necessity. The demand for this preliminary exposition becomes more urgent as we recognize that Leibniz's remarks upon Locke are not a critique of Locke from the standpoint of the latter, but are the application of his own philosophical conclusions. Criticism from within, an examination of a system of thought with relation to the consistency and coherency of its results, the connection between these results and the method professedly employed, investigation which depends not at all upon the position of the critic, but occupies itself with the internal relations of the system under discussion,--such criticism is a product of the present century. What we find in the "Nouveaux Essais" is a comparison of the ideas of Locke with those of Leibniz himself, a testing of the former by the latter as a standard, their acceptance when they conform, their rejection when they are opposed, their completion when they are in partial harmony.

The value of this sort of criticism is likely to be small and evanescent. If the system used as a standard is meagre and narrow, if it is without comprehensiveness and flexibility, it does not repay after-examination. The fact that the "Nouveaux Essais" of Leibniz have escaped the oblivion of the philosophical criticism of his day is proof, if proof still be needed, of the reasoned basis, the width of grasp, the fertility of suggestion which characterize the thought of Leibniz. But the fact that the criticism is, after all, external and not internal has made necessary the foregoing extended account of his method and general results.

On the other hand, what of Locke? How about him who is the recipient of the criticism? I a.s.sume that no extended account of his ideas is here necessary, and conceive myself to be justified in this a.s.sumption by the fact that we are already better acquainted with Locke. This acquaintance, indeed, is not confined to those who have expressly studied Locke. His thought is an inheritance into which every English-speaking person at least is born. Only he who does not think escapes this inheritance. Locke did the work which he had to do so thoroughly that every Englishman who will philosophize must either build upon Locke's foundations, or, with conscious purpose, clear the ground before building for himself. And it would be difficult to say that the acceptance of Locke's views would influence one's thought more than their rejection. This must not, of course, be taken too literally. It may be that one who is a lineal descendant of Locke in the spiritual generations of thought would not state a single important truth as Locke stated it, or that those who seek their method and results elsewhere have not repudiated the thought of Locke as expressly belonging to him.

But the fundamental principles of empiricism: its conception of intelligence as an individual possession; its idea of reality as something over against and distinct from mind; its explanation of knowledge as a process of action and reaction between these separate things; its account of our inability to know things as they really are,--these principles are congenital with our thinking. They are so natural that we either accept them as axiomatic, and accuse those who reject them of metaphysical subtlety, or, staggered perchance by some of their results, give them up with an effort. But it is an effort, and a severe one; and there is none of us who can tell when some remnant of the conception of intelligence as purely particular and finite will catch him tripping. On the other hand, we realize much better than those who have behind them a Leibniz and a Kant, rather than a Locke and a Hume, the meaning and the thorough-going necessity of the universality of intelligence. Idealism must be in some ways arbitrary and superficial to him who has not had a pretty complete course of empiricism.

Leibniz seems to have been impressed with the Essay on the Human Understanding at its first appearance. As early as 1696 we find him writing a few pages of comment upon the book. Compared with his later critique, these early "reflections" seem colorless, and give the impression that Leibniz desired to minimize his differences from Locke rather than to set them forth in relief. Comparatively slight as were his expressions of dissent, they appear to have stung Locke when they reached him. Meantime Locke's book was translated into French, and made its way to a wider circle of readers. This seems to have suggested to Leibniz the advisability of pursuing his comments somewhat further; and in the summer of 1703 he produced the work which now occupies us. A letter which Leibniz wrote at about this time is worth quoting at large for the light which it throws upon the man, as well as for suggesting the chief points in which he differed from Locke. Leibniz writes:--

"I have forgotten to tell you that my comments upon the work of Locke are nearly done. As he has spoken in a chapter of his second book about freedom, he has given me an opportunity to discuss that; and I hope that I may have done it in such a way as will please you. Above all, I have laid it upon myself to save the immateriality of the soul, which Locke leaves doubtful. I justify also the existence of innate ideas, and show that the soul produces their perception out of itself. Axioms, too, I approve, while Locke has a low opinion of them. In contradiction to him, I show that the individuality of man, through which he preserves his ident.i.ty, consists in the duration of the simple or immaterial substance which animates him; that the soul is never without representations; that there is neither a vacuum nor atoms; that matter, or the pa.s.sive principle, cannot be conscious, excepting as G.o.d unites with it a conscious substance. We disagree, indeed, in numerous other points, for I find that he rates too low the n.o.ble philosophy of the Platonic school (as Descartes did in part), and subst.i.tutes opinions which degrade us, and which may become hurtful to morals, though I am persuaded that Locke's intention was thoroughly good. I have made these comments in leisure hours, when I have been journeying or visiting, and could not occupy myself with investigations requiring great pains. The work has continued to grow under my hands, for in almost every chapter, and to a greater extent than I had thought possible, I have found matter for remark. You will be astonished when I tell you that I have worked upon this as upon something which requires no great pains. But the fact is, that I long ago established the general principles of philosophic subjects in my mind in a demonstrative way, or pretty nearly so, and that they do not require much new consideration from me."

Leibniz goes on to add that he has put these reflections in the form of a dialogue that they may be more attractive; has written them in the popular language, rather than in Latin, that they may reach as wide a circle as the work of Locke; and that he hopes to publish them soon, as Locke is already an old man, and he wishes to get them before the public while Locke may still reply.

But unfortunately this last hope was destined to remain unrealized. Before the work of revision was accomplished, Locke died. Leibniz, in a letter written in 1714, alludes to his controversy with Locke as follows: "I do not like the thought of publishing refutations of authors who are dead. These should appear during their life, and be communicated to them." Then, referring to his earlier comments, he says: "A few remarks escaped me, I hardly know how, and were taken to England. Mr. Locke, having seen them, spoke of them slightingly in a letter to Molineux. I am not astonished at it. We were somewhat too far apart in principle, and that which I suggested seemed paradoxical to him." Leibniz, according to his conviction here expressed, never published his "Nouveaux Essais sur l'Entendement Humain." Schaarschmidt remarks that another reason may have restrained him, in that he did not wish to carry on too many controversies at once with the English people. He had two on his hands then,--one with the Newtonians regarding the infinitesimal calculus; the other with Bishop Clarke regarding the nature of G.o.d, of time and s.p.a.ce, of freedom, and cognate subjects. However, in 1765, almost fifty years after the death of Leibniz, his critique upon Locke finally appeared.

It is somewhat significant that one whose tendency was conciliatory, who was eminently what the Germans delight to call him, a "mediator,"

attempting to unite the varied truths which he found scattered in opposed systems, should have had so much of his work called forth by controversy. Aside from the cases just mentioned, his other chief work, the Theodicy, is, in form, a reply to Bayle. Many of his minor pieces are replies to criticism or are developments of his own thought with critical reference to Descartes, Malebranche, and others. But Leibniz has a somewhat different att.i.tude towards his British and towards his Continental opponents. With the latter he was always in sympathy, while they in turn gave whatever he uttered a respectful hearing. Their mutual critiques begin and end in compliments. But the Englishmen found the thought of Leibniz "paradoxical" and forced. It seemed to them wildly speculative, and indeed arbitrary guess-work, without any special reason for its production, and wholly unverifiable in its results. Such has been the fate of much of the best German thought since that time in the land of the descendants of Newton and Locke. But Leibniz, on the other hand, felt as if he were dealing, in philosophical matters at least, with foemen hardly worthy of his steel. Locke, he says, had subtlety and address, and a sort of _superficial_ metaphysics; but he was ignorant of the method of mathematics,--that is to say, from the standpoint of Leibniz, of the method of all science. We have already seen that he thought the examination of a work which had been the result of the continued labor of Locke was a matter for the leisure hours of his courtly visits. Indeed, he would undoubtedly have felt about it what he actually expressed regarding his controversy with Clarke,--that he engaged in it

"Ludus et jocus, quia in philosophia Omnia percepi atque animo mec.u.m ante peregi."

He regarded the English as superficial and without grasp of principles, as they thought him over-deep and over-theoretical.

From this knowledge of the external circ.u.mstances of the work of Leibniz and its relation to Locke, it is necessary that we turn to its internal content, to the thought of Leibniz as related to the ideas of Locke. The Essay on the Human Understanding is, as the name implies, an account of the nature of knowledge. Locke tells us that it originated in the fact that often, when he had been engaged in discussions with his friends, they found themselves landed in insoluble difficulties. This occurred so frequently that it seemed probable that they had been going at matters from the wrong side, and that before they attempted to come to conclusions about questions they ought to examine the capacity of intelligence, and see whether it is fitted to deal with such questions. Locke, in a word, is another evidence of that truth which lies at the basis of all forms of philosophical thought, however opposed they may be to one another,--the truth that knowledge and reality are so organic to each other that to come to any conclusion about one, we must know something about the other. Reality equals objects known or knowable, and knowledge equals reality dissolved in ideas,--reality which has become translucent through its meaning.

Locke's Essay is, then, an account of the origin, nature, extent, and limitations of human knowledge. Such is its subject-matter. What is its method? Locke himself tells us that he uses the "plain historical method." We do not have to resort to the forcing of language to learn that this word "historical" contains the key to his work. Every page of the Essay is testimony to the fact that Locke always proceeds by inquiring into the way and circ.u.mstances by which knowledge of the subject under consideration came into existence and into the conditions by which it was developed. Origin means with Locke, not logical dependence, but temporal production; development means temporal succession. In the language of our day, Locke's Essay is an attempt to settle ontological questions by a psychological method. And as we have before noticed, Leibniz meets him, not by inquiry into the pertinence of the method or into the validity of results so reached, but by the more direct way of impugning his psychology, by subst.i.tuting another theory of the nature of mind and of the way in which it works.

The questions with which the discussion begins are as to the existence of innate ideas, and as to whether the soul always thinks,--questions which upon their face will lead the experienced reader of to-day to heave a sigh in memory of hours wasted in barren dispute, and which will create a desire to turn elsewhere for matter more solid and more nutritive. But in this case, under the form which the discussion takes at the hands of Leibniz, the question which awaits answer under the meagre and worn-out formula of "innate ideas" is the function of intelligence in experience.

Locke denies, and denies with great vigor, the existence of innate ideas. His motives in so doing are practical and theoretical. He sees almost every old idea, every hereditary prejudice, every vested interest of thought, defended on the ground that it is an innate idea. Innate ideas were sacred, and everything which could find no defence before reason was an innate idea. Under such circ.u.mstances he takes as much interest in demolishing them as Bacon took in the destruction of the "eidols." But this is but a small portion of the object of Locke. He is a thorough-going empiricist; and the doctrine of innate ideas appears to offer the greatest obstacle to the acceptance of the truth that all the furnishing of the intellect comes from experience. Locke's metaphors for the mind are that it is a blank tablet, an empty closet, an unwritten book. The "innate idea" is only a sentence written by experience, but which, deified by a certain school of philosophers, has come to be regarded as eternally imprinted upon the soul.

Such, indeed, is Locke's understanding of the nature of innate ideas. He conceives of them as "characters _stamped_, as it were, upon the mind of man, which the soul has received in its first being and brings into the world with it;" or they are "constant _impressions_ which the souls of men receive in their first beings." They are "truths _imprinted_ upon the soul." Having this conception of what is meant by "innate ideas," Locke sets himself with great vigor, and, it must be confessed, with equal success, to their annihilation.

His argument is somewhat diffuse and scattered, but in substance it is as follows: Whatever is in the mind, the mind must be conscious of. "To be in the mind and not to be perceived, is all one as to say that anything is and is not in the mind." If there be anything in the mind which is innate, it must be present to the consciousness of all, and, it would seem, of all at all times, savages, infants, and idiots included. And as it requires little philosophical penetration to see that savages do not ponder upon the principle that whatever is, is; that infants do not dwell in their cradle upon the thought of contradiction, or idiots ruminate upon that of excluded middle,--it ought to be evident that such truths cannot be innate. Indeed, we must admit, with Locke, that probably few men ever come to the explicit consciousness of such ideas, and that these few are such as direct their minds to the matter with some pains. Locke's argument may be summed up in his words: If these are not notions naturally imprinted, how can they be innate? And if they are notions naturally imprinted, how can they be unknown?

But since it may be said that these truths are in the mind, but in such a way that it is only when they are proposed that men a.s.sent to them, Locke goes on to clinch his argument. If this be true, it shows that the ideas are not innate; for the same thing is true of a large number of scientific truths, those of mathematics and morals, as well as of purely sensible facts, as that red is not blue, sweet is not sour, etc.,--truths and facts which no one calls innate. Or if it be said that they are in the mind implicitly or potentially, Locke points out that this means either nothing at all, or else that the mind is _capable_ of knowing them. If this is what is meant by innate ideas, then all ideas are innate; for certainly it cannot be denied that the mind is capable of knowing all that it ever does know, or, as Locke ingenuously remarks, "n.o.body ever denied that the mind was capable of knowing several truths."

It is evident that the force of Locke's contention against innate ideas rests upon a certain theory regarding the nature of innate ideas and of the relations of consciousness to intelligence. Besides this, there runs through his whole polemic the a.s.sertion that, after all, innate ideas are useless, as experience, in the sense of impressions received from without, and the formal action of intelligence upon them, is adequate to doing all they are supposed to do. It is hardly too much to say that the nerve of Locke's argument is rather in this positive a.s.sertion than in the negations which he brings against this existence. Leibniz takes issue with him on each of these three points. He has another conception of the very nature of innate ideas; he denies Locke's opinions about consciousness; he brings forward an opposed theory upon the relation of experience to reason. This last point we shall take up in a chapter by itself, as its importance extends far beyond the mere question as to the existence of ideas which may properly be called innate. The other two questions, as to the real character of innate ideas and the relation of an idea to consciousness, afford material to occupy us for the present.

The metaphor which Locke constantly uses is the clew to his conception of innate ideas. They are characters stamped or imprinted upon the mind, they exist _in_ the mind. The mind would be just what it is, even if they had no existence. It would not have quite so much "in"

it, but its own nature would not be changed. Innate ideas he conceives as bearing a purely external relation to mind. They are not organic to it, nor necessary instruments through which it expresses itself; they are mechanically impressed upon it. But what the "intellectual"

school had meant by innate ideas was precisely that the relation of ideas to intelligence is _not_ that of pa.s.sive holding or containing on the side of mind, and of impressions or stamps on the side of the ideas. Locke reads the fundamental category of empiricism--mechanical relation, or external action--into the nature of innate ideas, and hence easily infers their absurdity. But the object of the upholders of innate ideas had been precisely to deny that this category was applicable to the whole of intelligence. By an innate idea they meant an a.s.sertion of the dynamic relation of intelligence and some of its ideas. They meant to a.s.sert that intelligence has a structure, which necessarily functions in certain ways. While Locke's highest conception of an innate idea was that it must be something ready made, dwelling in the mind prior to experience, Leibniz everywhere a.s.serts that it is a connection and relation which forms the logical prius and the psychological basis of experience. He finds no difficulty in admitting all there is of positive truth in Locke's doctrine; namely, that we are not conscious of these innate ideas until a period later than that in which we are conscious of sensible facts, or, in many cases, are not conscious of them at all. This priority in time of sensible experience to rational knowledge, however, can become a reason for denying the "innate" character of the latter only when we suppose that they are two entirely different orders of fact, one knowledge due to experience, the other knowledge already formed and existing in the mind prior to "experience."

Leibniz's conception of the matter is brought out when he says that it is indeed true that we begin with particular experiences rather than with general principles, but that the order of nature is the reverse, for the ground, the basis of the particular truths is in the general; the former being in reality only instances of the latter. General principles, he says, enter into _all_ our thoughts, and form their soul and interconnection. They are as necessary for thought as muscles and tendons are for walking, although we may not be conscious of their existence. This side of the teaching of Leibniz consists, accordingly, in the a.s.sertion that "innate" knowledge and knowledge derived from experience are not two kinds of knowledge, but rather two ways of considering it. If we consider it as it comes to us, piecemeal and fragmentary, a succession of particular instances, to be gathered up at a future time into general principles, and stated in a rational form, it is seen as empirical. But, after all, this is only a superficial and external way of looking at it. If we examine into it we shall see that there are contained in these transitory and particular experiences certain truths more general and fundamental, which condition them, and at the same time const.i.tute their meaning.

If we inquire into the propriety of calling these truths "innate,"

we find it is because they are native to intelligence, and are not acquisitions which it makes. Indeed, it may be said that they _are_ intelligence, so close and organic is their relation, just as the muscles, the tendons, the skeleton, are the body. Thus it is that Leibniz accepts the statement, _Nihil est in intellectu quod non fuerit in sensu_, with the addition of the statement _nisi ipse intellectus_. The doctrine of the existence of innate ideas is thus shown to mean that intelligence exists with a real content which counts for something in the realm of experience. If we take intelligence and examine into its structure and ascertain its modes of expression, we find organically inherent in its activity certain conceptions like unity, power, substance, ident.i.ty, etc., and these we call "innate." An idea, in short, is no longer conceived as something existing in the mind or in consciousness; it is an activity of intelligence. An innate idea is a necessary activity of intelligence; that is, such an activity as enters into the framework of all experience.

Leibniz thus succeeds in avoiding two errors into which philosophers whose general aims are much like his have fallen. One is dividing _a priori_ and _a posteriori_ truths from each other by a hard and fixed line, so that we are conceived to have some knowledge which comes wholly from experience, while there is another which comes wholly from reason. According to Leibniz, there is no thought so abstract that it does not have its connection with a sensible experience, or rather its embodiment in it. And, on the other hand, there is no experience so thoroughly sensuous that it does not bear in itself traces of its origin in reason. "_All_ our thoughts come from the depths of the soul," says Leibniz; there are none that "come" to us from without. The other error is the interpretation of the existence of innate ideas or "intuitions" (as this school generally calls them) in a purely formal sense. They are thus considered as truths contained in and somehow expressed by intelligence, but yet not so connected with it that in knowing them we necessarily know intelligence itself. They are considered rather as arbitrary determinations of truths by a power whose own nature is conceivably foreign to truth, than as so many special developments of an activity which may indifferently be called "intelligence" or "truth." Leibniz, however, never fails to state that an innate truth is, after all, but one form or aspect of the activity of the mind in knowing.

In this way, by bringing to light a deeper and richer conception of what in reality const.i.tutes an innate idea, Leibniz answers Locke. His reply is indirect; it consists rather in throwing a flood of new light upon the matter discussed, than in a ponderous response and counter-attack. But when Leibniz touches upon the conception of a _tabula rasa_, of a mind which in itself is a mere blank, but has the capacity for knowing, he a.s.sumes the offensive. The idea of a bare capacity, a formal faculty, of power which does not already involve some actual content within itself, he repudiates as a relic of scholasticism. What is the soul, which has nothing until it gets it from without? The doctrine of a vacuum, an emptiness which is real, is always absurd; and it is doubly so when to this vacuum is ascribed powers of feeling and thinking, as Locke does. Accepting for the moment the metaphor of a _tabula rasa_, Leibniz asks where we shall find a tablet which yet does not have some quality, and which is not a co-operating cause, at least, in whatever effects are produced upon it? The notion of a soul without thought, an empty tablet of the soul, he says, is one of a thousand fictions of philosophers. He compares it with the idea of "s.p.a.ce empty of matter, absolute uniformity or h.o.m.ogeneity, perfect spheres of the second element produced by primordial perfect cubes, abstractions pure and simple, to which our ignorance and inattention give birth, but of which reality does not admit." If Locke admits then (as he does) certain capacities inherent in the soul, he cannot mean the scholastic fiction of bare capacity or mere possibility; he must mean "real possibilities,"--that is, capacities accompanied with some actual tendency, an inclination, a disposition, an apt.i.tude, a preformation which determines our soul in a certain direction, and which makes it necessary that the possibility becomes actual. And this tendency, this actual inclination of intelligence in one way rather than another, so that it is not a matter of indifference to intelligence what it produces, is precisely what const.i.tutes an innate idea. So Leibniz feels certain that at bottom Locke must agree with him in this matter if the latter is really in earnest in rejecting the "faculties" of the scholastics and in wishing for a real explanation of knowledge.

But the argument of Locke rests upon yet another basis. He founds his denial of innate ideas not only upon a static conception of their ready made existence "in" the soul, but also upon an equally mechanical conception of consciousness. "Nothing can be in the mind which is not in consciousness." This statement appears axiomatic to Locke, and by it he would settle the whole discussion. Regarding it, Leibniz remarks that if Locke has such a prejudice as this, it is not surprising that he rejects innate ideas. But consciousness and mental activity are not thus identical. To go no farther, the mere empirical fact of memory is sufficient to show the falsity of such an idea. Memory reveals that we have an indefinite amount of knowledge of which we are not always conscious. Rather than that knowledge and consciousness are one, it is true that actual consciousness only lays hold of an infinitesimal fraction of knowledge. But Leibniz does not rely upon the fact of memory alone. We must constantly keep in mind that to Leibniz the soul is not a form of being wholly separate from nature, but is the culmination of the system of reality. The reality is everywhere the monad, and the soul is the monad with the power of feeling, remembering, and connecting its ideas. The activities of the monad, those representative changes which sum up and symbolize the universe, do not cease when we reach the soul. They are continued. If the soul has the power of attention, they are potentially conscious. Such as the soul actually attends to, thus giving them relief and making them distinct, are actually conscious. But all of them exist.

Thus it is that Leibniz not only denies the equivalence of soul and consciousness, but a.s.serts that the fundamental error of the psychology of the Cartesians (and here, at least, Locke is a Cartesian) is in identifying them. He a.s.serts that "unconscious ideas" are of as great importance in psychology as molecules are in physics. They are the link between unconscious nature and the conscious soul. Nothing happens all at once; nature never makes jumps; these facts stated in the law of continuity necessitate the existence of activities, which may be called ideas, since they belong to the soul and yet are not in consciousness.

When, therefore, Locke asks how an innate idea can exist and the soul not be conscious of it, the answer is at hand. The "innate idea"

exists as an activity of the soul by which it represents--that is, expresses--some relation of the universe, although we have not yet become conscious of what is contained or enveloped in this activity. To become conscious of the innate idea is to lift it from the sphere of nature to the conscious life of spirit. And thus it is, again, that Leibniz can a.s.sert that all ideas whatever proceed from the depths of the soul. It is because it is the very being of the soul as a monad to reflect "from its point of view" the world. In this way Leibniz brings the discussion regarding innate ideas out of the plane of examination into a matter of psychological fact into a consideration of the essential nature of spirit. An innate idea is now seen to be one of the relations by which the soul reproduces some relation which const.i.tutes the universe of reality, and at the same time realizes its own individual nature. It is one reflection from that spiritual mirror, the soul. With this enlarged and transformed conception of an idea apt to be so meagre we may well leave the discussion. There has been one mind at least to which the phrase "innate ideas" meant something worth contending for, because it meant something real.

CHAPTER V.

SENSATION AND EXPERIENCE.

A careful study of the various theories which have been held concerning sensation would be of as much interest and importance as an investigation of any one point in the range of philosophy. In the theory of a philosopher about sensation we have the reflex of his fundamental category and the clew to his further doctrine. Sensation stands on the border-line between the world of nature and the realm of soul; and every advance in science, every development of philosophy, leaves its impress in a change in the theory of sensation. Apparently one of the simplest and most superficial of questions, in reality it is one of the most difficult and far-reaching. At first sight it seems as if it were a sufficient account of sensation to say that an object affects the organ of sense, and thus impresses upon the mind the quality which it possesses. But this simple statement arouses a throng of further questions: How is it possible that one substance,--matter,--should affect another,--mind? How can a causal relation exist between them? Is the mind pa.s.sive or active in this impression? How can an object convey unchanged to the mind a quality which it possesses? Or is the sensational _quale_ itself a product of the mind's activity? If so, what is the nature of the object which excites the sensation? As known, it is only a collection of sensuous qualities; if these are purely mental, what becomes of the object? And if there is no object really there, what is it that excites the sensation? Such questionings might be continued almost indefinitely; but those given are enough to show that an examination of the nature and origin of sensation introduces us to the problems of the relation of intelligence and the world; to the problem of the ultimate const.i.tution of an object which is set over against a subject and which affects it; and to the problem of the nature of mind, which as thus affected from without must be limited in its nature, but which as bearer of the whole known universe must be in some sense infinite. If we consider, not the mode of production of sensation, but its relation to knowledge, we find philosophical schools divided into two,--Sensationalists, and Rationalists. If we inquire into its functions, we find that the empiricist sees in it convincing evidence of the fact that all knowledge originates from a source _extra mentem_; that the intellectual idealist finds in it evidence of the gradual transition of nature into spirit; that the ethical idealist, like Kant and Fichte, sees in it the material of the phenomenal world, which is necessary in its opposition to the rational sphere in order that there may occur that conflict of pure law and sensuous impulse which alone makes morality possible. We thus realize that as we look at the various aspects of sensation, we are taken into the discussion of ontology, of the theory of knowledge and of ethics.

Locke virtually recognizes the extreme importance of the doctrine of sensation, and his second book might almost be ent.i.tled "Concerning the Nature and Products of Sensation." On the other hand, one of the most characteristic and valuable portions of the reply of Leibniz is in his development of a theory of sensation which is thoroughly new, except as we seek for its germs in its thoughts of Plato and Aristotle. According to Locke, knowledge originates from two sources,--sensation and reflection. Sensations are "the impressions made on our senses by outward objects that are extrinsic to the mind." When the mind "comes to reflect on its own operations about the ideas got by sensation, and thereby stores itself with a new set of ideas," it gets ideas of reflection.

If we leave out of account for the present the ideas of reflection, we find that the ideas which come through sensation have two main characteristics. First, in having sensations, the mind is pa.s.sive; its part is purely receptive. The objects impress themselves upon the mind, they obtrude into consciousness, whether the mind will or not. There is a purely external relation existing between sensation and the understanding. The ideas are offered to the mind, and the understanding cannot refuse to have them, cannot change them, blot them out, nor create them, any more than a mirror can refuse, alter, or obliterate the images which objects produce in it. Sensation, in short, is a purely pa.s.sive having of ideas. Secondly, every sensation is simple. Locke would say of sensations what Hume said of all ideas,--every distinct sensation is a separate existence. Every sensation is "uncompounded, containing nothing but one uniform appearance, not being distinguishable into different ideas." Knowledge is henceforth a process of compounding, of repeating, comparing, and uniting sensation. Man's understanding "reaches no further than to compound and divide the materials that are made to his hand."

It hardly need be said that Locke has great difficulty in keeping up this thoroughly atomic theory of mind. It is a theory which makes all relations external; they are, as Locke afterwards says, "superinduced"

upon the facts. It makes it impossible to account for any appearance of unity and connection among ideas, and Locke quietly, and without any consciousness of the contradiction involved, introduces certain inherent relations into the structure of the ideas when he comes to his constructive work. "Existence and unity are two ideas," he says, "that are suggested to the understanding by every object without, and every idea within."

At other places he introduces the idea of quality of a substance, effect of a cause, continued permanence or ident.i.ty into a sensation, as necessary const.i.tuents of it; thus making a sensation a unity of complex elements instead of an isolated bare notion. How far he could have got on in his account of knowledge without this surrept.i.tious qualifying of a professedly simple existence, may be seen by asking what would be the nature of a sensation which did not possess existence and unity, and which was not conceived as the quality of a thing or as the effect of an external reality.

This digression has been introduced at this point because the next character of a sensation which Locke discusses is its objective character,--its relation to the object which produces it. To discourse of our ideas intelligibly, he says, it will be convenient to distinguish them as they are ideas in our minds and as they are modifications of matter in the bodies that cause them. In other words, he gives up all thought of considering ideas as simply mental modifications, and finds it necessary to take them in their relations to objects.

Taking them in this way, he finds that they are to be divided into two cla.s.ses, of which one contains those ideas that are copies and resemblances of qualities in the objects, ideas "which are really in the object, whether we take notice of them or no,"--in which case we have an idea of the thing as it is in itself; while the other cla.s.s contains those which are in no way resemblances of the objects which produce them, "having no more similitude than the idea of pain and of a sword." The former are primary qualities, and are solidity, extension, figure, motion or rest, and number; while the secondary qualities are colors, smells, and tastes. The former ideas are produced by impulse of the bodies themselves, which simply effect a transference of their qualities over into the mind; while the secondary qualities are arbitrarily annexed by the power of G.o.d to the objects which excite them.

It will be noticed that there are two elements which make the sensation of Locke what it is. With reference to its _production_, it is the effect which one substance, matter, has upon another substance, mind, which is unlike it in nature, and between which whatever relations exist, are thoroughly incomprehensible, so that, indeed, their connections with each other can be understood only by recourse to a _tertium quid_, an omnipotent power which can arbitrarily produce such collocations as please it. With reference to its _function_, it is the isolated and "simple" (that is, non-relational) element out of which all actual forms of knowledge are made by composition and re-arrangement.

Leibniz, without entering into explicit criticism of just these two points, develops his own theory with reference to them. To Leibniz, reality const.i.tutes a system; that is, it is of such a nature that its various portions have an essential and not merely external relation to one another. Sensation is of course no exception. It is not a mere accident, nor yet a supernatural yoking of things naturally opposed. It has a meaning in that connection of things which const.i.tute the universe. It contributes to the significance of the world. It is one way in which those activities which make the real express themselves. It has its place or reason in the totality of things, and this whether we consider its origin or its position with regard to knowledge. In a word, while the characteristic of Locke's theory is that he conceives sensation as in external relation both to reality, as mechanically produced by it, and to knowledge, as being merely one of the atomic elements which may enter into a compound, Leibniz regards reality as organic to sensation, and this in turn as organic to knowledge. We have here simply an ill.u.s.tration of the statement with which we set out; namely, that the treatment of sensation always reflects the fundamental philosophical category of the philosopher.

All reality exists in the form of monads; monads are simple substances whose nature is action; this action consists in representing, according to a certain law of succession, the universe. Various monads have various degrees of activity; that is, of the power of reflecting the world. So much of Leibniz's general philosophical att.i.tude it is necessary to recall, to understand what he means by "sensation." The generic name which is applied to this mirroring activity of the monads is "perception," which, as Leibniz often says, is to be carefully distinguished from apperception, which is the representation become conscious. Perception may be defined, therefore, as the inclusion of the many or multiform (the world of objects) in a unity (the simple substance). It was the great defect of previous philosophy that it "considered only spirits or self-conscious beings as souls," and had consequently recognized only conscious perceptions. It had been obliged, therefore, to make an impa.s.sable gulf between mind and matter, and sensations were thus rendered inexplicable. But Leibniz finds his function as a philosopher in showing that these problems, which seem insoluble, arise when we insist upon erecting into actual separations or differences of kind what really are only stages of development or differences of degree. A sensation is not an effect which one substance impresses upon another because G.o.d pleased that it should, or because of an incomprehensible incident in the original const.i.tution of things. It is a higher development of that representative power which belongs to every real being.

Certain monads reach a state of development, or manifestation of activity, which is characterized by the possession of distinct organs. Such monads may be called, in a pre-eminent sense, "souls,"

and include all the higher animals as well as man. This possession of differentiated organs finds its a.n.a.logue in the internal condition of the monad. What appears externally as an organ of sense appears ideally as a conscious representative state which we call "sensation." "When,"

Leibniz says, "the monad has its organs so developed that there is relief and differentiation in the impressions received, and consequently in the perceptions which represent them, we have feeling or sensation; that is, a perception accompanied by memory," to which at other times he adds "attention." Life, he says, "is a perceptive principle; the soul is sensitive life; mind is rational soul." And again he says in substance that when the soul begins to have interests, and to regard one representation as of more value than others, it introduces relief into its perceptions, and those which stand out are called "sensations."

This origin of sensations as higher developments of the representative activities of a monad conditions their relation to further processes of knowledge. The sensations are confused knowledge; they are ideas in their primitive and most undifferentiated form. They const.i.tute, as Leibniz somewhere says, the vertigo of the conscious life. In every sentient organism mult.i.tudes of sensations are constantly thronging in and overpowering its distinct consciousness. The soul is so flooded with ideas of everything in the world which has any relation to its body that it has distinct ideas of nothing. Higher knowledge, then, does not consist in compounding these sensations; that would literally make confusion worse confounded. It consists in introducing distinctness into the previously confused sensations,--in finding out what they mean; that is, in finding out their bearings, what they point to, and how they are related. Knowledge is not an external process performed upon the sensations, it is the development of their internal content.

It follows, therefore, that sensation is organic to all forms of knowledge whatever. The monad, which is pure activity, that which culminates the scale of reality, has no confused ideas, and to it all knowledge is eternally rational, having no sensible traces about it. But every other monad, having its activity limited, has ideas which come to it at first in a confused way, and which its activity afterwards differentiates. Thus it is that Leibniz can agree so heartily with the motto of the Sensationalist school,--that there is nothing in the intellect which was not first in the sensory. But Leibniz uses this phrase as Aristotle would have done, having in mind the distinction between potentiality and actuality. _In posse_, sensation is all knowledge; but only _in posse_. And he, like Aristotle, interprets the relation between potentiality and actuality as one of a difference of activity. The potential is that which becomes real through a dynamic process. The actual is capacity plus action. Sensation, in short, is spiritual activity in an undeveloped and hence partial and limited condition. It is not, as Locke would have it, the real factor in all knowledge.