"Were it fit to trouble thee," says Locke in his Epistle to the Reader, "with the history of this Essay, I should tell thee that five or six friends meeting at my chamber, and discoursing on a subject very remote from this, found themselves quickly at a stand by the difficulties that rose on every side. After we had a while puzzled ourselves, without coming any nearer a resolution of those doubts which perplexed us, it came into my thoughts that we took a wrong course; and that, before we set ourselves upon inquiries of that nature, it was necessary to examine our own abilities, and see what objects our understandings were or were not fitted to deal with. This I proposed to the company, who all readily assented; and thereupon it was agreed that this should be our first inquiry."

This passage may serve not only to describe the occasion of Locke's Essay, but also to indicate the circumstance which constitutes the peculiar merit and originality of Locke as a philosopher. The science which we now call Psychology, or the study of mind, had hitherto, amongst modern writers, been almost exclusively subordinated to the interests of other branches of speculation. Some exception must, indeed, be made in favour of Hobbes and Gassendi, Descartes and Spinoza; but all these authors treated the questions of psychology somewhat cursorily, while the two former seem usually to have had in view the illustration of some favourite position in physics or ethics, the two latter the ultimate establishment of some proposition relating to the nature or attributes of God. We may say then, without much exaggeration, that Locke was the first of modern writers to attempt at once an independent and a complete treatment of the phenomena of the human mind, of their mutual relations, of their causes and limits. His object was, as he himself phrases it, "to inquire into the original, certainty, and extent of human knowledge; together with the grounds and degrees of belief, opinion, and assent." This task he undertakes not in the dogmatic spirit of his predecessors, but in the critical spirit which he may be said to have almost inaugurated. As far as it is possible for a writer to divest himself of prejudice, and to set to his work with a candid and open mind, seeking help and information from all quarters, Locke does so. And the effect of his candour on his first readers must have been enhanced by the fact, not always favourable to his precision, that, as far as he can, he throws aside the technical terminology of the schools, and employs the language current in the better kinds of ordinary literature and the well-bred society of his time. The absence of pedantry and of parti pris in a philosophical work was at that time so rare a recommendation that, no doubt, these characteristics contributed largely to the rapid circulation and the general acceptance of the Essay.

The central idea, which dominates Locke's work, is that all our knowledge is derived from experience. But this does not strike us so much as a thesis to be maintained as a conclusion arrived at after a vast amount of patient thought and inquiry. Have we any ideas independent of experience? or, as Locke phrases it, are there any Innate Principles in the mind?

"It is an established opinion amongst some men that there are in the Understanding certain Innate Principles, some Primary Notions, ????a? ?????a? [Greek: koinai ennoiai], characters, as it were, stamped upon the mind of man, which the Soul receives in its very first being and brings into the world with it."

This is the opinion which Locke examines and refutes in the first, or introductory, book of the Essay. It has often been objected that he mistakes and exaggerates the position which he is attacking. And so far as his distinguished predecessor, Descartes, is concerned (though to what extent Locke has him in mind, his habit of not referring to other authors by name prevents us from knowing), this is undoubtedly the case. For Descartes, though he frequently employs and accepts the expression "innate notions" or "innate ideas," concedes, as so many philosophers of the same school have done since, that this native knowledge is only implicit, and requires definite experiences to elicit it. Thus, in his notes on the Programme of Regius, he expressly compares these innate notions or ideas with the nobility which is characteristic of certain ancient stocks, or with diseases, such as gout or gravel, which are said to be "innate" in certain families, not "because the infants of those families suffer from these diseases in their mother's womb, but because they are born with a certain disposition or tendency to contract them." Here Descartes seems to have been on the very point of stumbling on the principle of heredity which, in the hands of recent physiologists and psychologists, has done so much towards reconciling rival theories on the nature and origin of knowledge and clearing up many of the difficulties which attach to this branch of speculation. It must be confessed, however, that in his better-known works he often employs unguarded and unexplained expressions which might easily suggest the crude form of the À priori theory attacked by Locke. Still more is this the case with other authors, such as Lord Herbert of Cherbury and Dr. Ralph Cudworth, whose works were in general circulation at the time when Locke was composing his Essay. Lord Herbert, though indeed he acknowledges that "common notions" (the expression by which he designates À priori principles) require an object to elicit them into consciousness, seems invariably to regard them as ready-made ideas implanted in the human mind from its very origin. They are given by an independent faculty, Natural Instinct, which is to be distinguished from Internal Sense, External Sense, and Reasoning ("discursus"), the sources of our other ideas. They are to be found in every man, and universal consent is the main criterion by which they are to be discriminated. In fact, there can be no doubt that the dogma of Innate Ideas and Innate Principles, in the form attacked by Locke, was a natural, if not the legitimate, interpretation of much of the philosophical teaching of the time, and that it was probably the form in which that teaching was popularly understood. It lay, moreover, as Locke's phrase is, along the "common road," which was travelled by the majority of men who cared about speculative subjects at all, and from which it was novel, and therefore dangerous, to diverge.

The most effective, perhaps, of Locke's arguments against this doctrine is his challenge to the advocates of Innate Principles to produce them, and show what and how many they are. Did men find such innate propositions stamped on their minds, nothing could be more easy than this. "There could be no more doubt about their number than there is about the number of our fingers; and 'tis like, then, every system would be ready to give them us by tale." Now "'tis enough to make one suspect that the supposition of such innate principles is but an opinion taken up at random; since those who talk so confidently of them are so sparing to tell us which they are." (Bk. I., ch. iii., § 14.) The great majority, indeed, of those who maintain the existence of innate principles and ideas attempt no enumeration of them. Those who do attempt such an enumeration differ in the lists which they draw up, and, moreover, as Locke shows in the case of the five practical principles of Lord Herbert of Cherbury, give no sufficient reason why many other propositions, which they regard as secondary and derived, should not be admitted to the same rank with the so-called innate principles, which they assume to be primary and independent. Locke is here treading on safer ground than in many of his other criticisms. The fact is that it is impossible clearly to discriminate between those propositions which are axiomatic and those which are derived—or, in the language of the theory which Locke is combating, between those which are innate and those which are adventitious. Race, temperament, mental capacity, habit, education, produce such differences between man and man that a proposition which to one man appears self-evident and unquestionable will by another be admitted only after considerable hesitation, while a third will regard it as doubtful, or even false. Especially is this the case, as Locke does not fail to point out, with many of the principles of religion and morals, which have now been received by so constant a tradition in most civilized nations that they have come to be regarded as independent of reason, and, if not "ingraven on the mind" from its birth, at least exempt from discussion and criticism. The circumstance, however, that they are not universally acknowledged shows that to mankind in general, at any rate, they are not axiomatic, and that, however clear and convincing the reasons for them may be, at all events those reasons require to be stated. It was this determined and vigorous protest against multiplying assumptions and attempting to withdraw a vast mass of propositions, both speculative and practical, from the control and revision of reason, that, perhaps, constituted the most distinctive and valuable part of Locke's teaching.

Having cleared from his path the theory of Innate Principles, Locke proceeds, in the Second Book, to inquire how the mind comes to be furnished with its knowledge. Availing himself of a metaphor which had been commonly employed by the Stoics, but which reaches as far back as Aristotle and Plato, and even as Æschylus, he compares the mind to "white paper, void of all characters, without any ideas," and then asks:

"Whence comes it by that vast store, which the busy and boundless Fancy of Man has painted on it, with an almost endless variety? Whence has it all the materials of Reason and Knowledge? To this I answer in one word, from Experience: In that all our knowledge is founded; and from that it ultimately derives itself. Our observation employed either about external or sensible objects, or about the internal operations of our minds perceived and reflected on by our selves, is that which supplies our Understandings with all the materials of thinking. These two are the Fountains of Knowledge from which all the ideas we have, or can naturally have, do spring."

"First, our Senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways in which those objects do affect them. And thus we come by those ideas we have of Yellow, White, Heat, Cold, Soft, Hard, Bitter, Sweet, and all those which we call Sensible Qualities, which when I say the senses convey into the mind, I mean they from external objects convey into the mind what produces there those Perceptions. This great source of most of the Ideas we have, depending wholly upon our senses, and derived by them to the Understanding, I call SENSATION."

"Secondly, the other Fountain, from which Experience furnisheth the Understanding with Ideas, is the Perception of the operations of our own minds within us, as it is employed about the ideas it has got; which operations, when the soul comes to reflect on and consider, do furnish the Understanding with another set of ideas which could not be had from things without; and such are Perception, Thinking, Doubting, Believing, Reasoning, Knowing, Willing, and all the different actings of our own minds, which we being conscious of, and observing in our selves, do from these receive into our Understandings as distinct ideas as we do from bodies affecting our senses. This source of ideas every man has wholly in himself. And though it be not sense, as having nothing to do with external objects, yet it is very like it, and might properly enough be called Internal Sense. But as I call the other Sensation, so I call this REFLECTION, the ideas it affords being such only as the mind gets by reflecting on its own operations within itself. By Reflection, then, in the following part of this Discourse, I would be understood to mean that notice which the mind takes of its own operations and the manner of them, by reason whereof there come to be Ideas of these operations in the Understanding. These two, I say, namely, external material things, as the objects of Sensation, and the operations of our own minds within, as the objects of Reflection, are to me the only originals from whence all our ideas take their beginning. The term operations here I use in a large sense, as comprehending not barely the actions of the mind about its ideas, but some sort of passions arising sometimes from them, such as is the satisfaction or uneasiness arising from any thought."

"The Understanding seems to me not to have the least glimmering of any ideas which it doth not receive from one of these two. External objects furnish the mind with the ideas of sensible qualities, which are all those different perceptions they produce in us; and the mind furnishes the Understanding with ideas of its own operations." (Bk. II., ch. i., §§ 2-5.)

In deriving our knowledge from two distinct sources, Sensation and Reflection, Locke is advancing a position altogether different from that of what is properly called the Sensationalist school of philosophers. Gassendi and Hobbes before him, Condillac and HelvÉtius after him, found the ultimate source of all our knowledge in the impressions of sense. The emphatic words of Hobbes, standing in the forefront of the Leviathan, are:—"The original of all the thoughts of men is that which we call Sense, for there is no conception in a man's mind which hath not at first, totally or by parts, been begotten upon the organs of sense." And Condillac, aiming at a theory still more simple, derives from sensations not only all our knowledge but all our faculties. "The other fountain," then, of Locke has, we must recollect, a peculiar significance as distinguishing his psychology from that of the sensationalist writers who preceded and who followed him. His theory of the origin of knowledge may fairly be called an experiential, but it cannot with any truth be called a sensationalist theory.

The rest of the Second Book of the Essay is mainly taken up with the attempt to enumerate our simple ideas of Sensation and Reflection, and to resolve into them our other ideas, however complex. To follow Locke into these details would be to re-write the Essay. I propose simply to direct the attention of the reader to a few salient points.

Of "Simple Ideas of Sensation," some "come into our minds by one Sense only." Such are the various colours, sounds, tastes, and smells, Heat and Cold, and the sensation of Resistance or Impenetrability, which Locke denominates Solidity. "The Ideas we get by more than one sense are of Space or Extension, Figure, Rest, and Motion."

The "Simple Ideas of Reflection," which the mind acquires, when "it turns its view inward upon itself, and observes its own actions about those ideas it has received from without," are mainly two, namely, Perception or Thinking, and Volition or Willing.

"There be other simple ideas, which convey themselves into the mind by all the ways of Sensation and Reflection, namely, Pleasure or Delight, Pain or Uneasiness, Power, Existence, Unity. (Bk. II., ch. vii., § 1.)

"These simple ideas, the materials of all our knowledge, are suggested and furnished to the mind only by those two ways above mentioned, namely, Sensation and Reflection. When the Understanding is once stored with these simple ideas, it has the power to repeat, compare, and unite them, even to an almost infinite variety, and so can make at pleasure new complex ideas. But it is not in the power of the most exalted Wit or enlarged Understanding, by any quickness or variety of thoughts, to invent or frame one new simple idea in the mind, not taken in by the ways before mentioned. Nor can any force of the Understanding destroy those that are there: the dominion of man, in this little world of his own understanding, being much-what the same as it is in the great world of visible things, wherein his power, however managed by art and skill, reaches no farther than to compound and divide the materials that are made to his hand, but can do nothing towards the making the least particle of new matter or destroying one atom of what is already in being. The same inability will every one find in himself who shall go about to fashion in his Understanding any simple idea not received in by his senses from external objects or by reflection from the operations of his own mind about them." (Bk. II., ch. ii., § 2.)

In the reception of these simple ideas, Locke regards the mind as merely passive. It can no more refuse to have them, alter or blot them out, than a mirror can refuse to receive, alter, or obliterate the images reflected on it. The Understanding, before the entrance of simple ideas, is like a dark room, and external and internal sensation are the windows by which light is let in. But when the light has once penetrated into this dark recess, the Understanding has an almost unlimited power of modifying and transforming it. It can create complex ideas, and that in an infinite variety, out of its simple ideas, and this it does chiefly by combining, comparing, and separating them.

"This shows man's power, and its way of operation, to be much what the same in the material and intellectual world. For the materials in both being such as he has no power over, either to make or destroy, all that man can do is either to unite them together, or to set them by one another, or wholly separate them." (Bk. II., ch. xii., § 1.)

The complex ideas are classified under three heads, modes, which may be either simple or mixed, substances, and relations. Here, however, my analysis must stop, and I must content myself with giving a few examples of the manner in which Locke attempts to resolve "complex ideas" into "simple" ones.

The idea of Infinity, to take one of his most celebrated resolutions, is merely a simple mode of Quantity, as Immensity is a simple mode of Space, and Eternity of Duration. All alike are negative ideas, arising whenever we allow the mind "an endless progression of thought," without any effort to arrest it. "How often soever" a man doubles an unit of space, be it a "mile, or diameter of the earth, or of the Orbis Magnus," or any otherwise multiplies it, "he finds that, after he has continued this doubling in his thoughts and enlarged his idea as much as he pleases, he has no more reason to stop, nor is one jot nearer the end of such addition, than he was at first setting out; the power of enlarging his idea of Space by farther additions remaining still the same, he hence takes idea of infinite space." (Bk. II., ch. xvii., § 3.)

With the idea of "Substance" Locke is fairly baffled. If we examine our idea of a horse, a man, a piece of gold, &c., we are able to resolve it into a number of simple ideas, such as extension, figure, solidity, weight, colour, &., co-existing together. But, according to Locke, who, in this respect, was merely following in the track of the generally received philosophy of his time, there is, in addition to all these qualities, a substratum in which they inhere, or, to use his own language, "wherein they do subsist, and from which they do result." Now of the various qualities we can form a clear idea and give a more or less intelligible account. But can we form a clear idea or give an intelligible account of the substratum? Locke here is bold enough to break off from the orthodox doctrine of the time, and confess candidly that we cannot. The idea of this Substratum or Substance is a "confused idea of something to which the qualities belong, and in which they subsist." The name Substance denotes a Support, "though it be certain we have no clear or distinct idea of that thing we suppose a support."

"So that if any one will examine himself concerning his notion of pure Substance in general, he will find he has no other idea of it at all but only a supposition of he knows not what Support of such qualities which are capable of producing simple ideas in us; which qualities are commonly called Accidents. If any one should be asked what is the subject wherein Colour or Weight inheres, he would have nothing to say but the solid extended parts. And if he were demanded what is it that Solidity and Extension inhere in, he would not be in a much better case than the Indian who, saying that the world was supported by a great elephant, was asked what the elephant rested on? To which his answer was, a great tortoise. But, being again pressed to know what gave support to the broad-backed tortoise, replied, something, he knew not what. And thus here, as in all other cases, where we use words without having clear and distinct ideas, we talk like children; who, being questioned what such a thing is, which they know not, readily give this satisfactory answer, That it is something; which in truth signifies no more, when so used, either by children or men, but that they know not what, and that the thing they pretend to know and talk of is what they have no distinct idea of at all, and so are perfectly ignorant of it and in the dark." (Bk. II., ch. xxiii., § 2.)

No wonder that the next step in philosophy was to get rid altogether of this "something, we know not what." For, if we know not what it is, how do we know that it exists, and is not a mere fiction of the Schools? This step was taken by Berkeley, as respects matter, and by Hume the same negative criticism which Berkeley confines to matter was boldly, and, as it seems to me, far less successfully and legitimately extended to mind. Indeed, were it not for his express assurance to the contrary, we should often be tempted to think that Locke himself regarded this distinction of Substance and Accident, so far, at least, as it affects Matter and its attributes, as untenable, and was anxious to insinuate a doubt as to the very existence of the "unknown somewhat."

In this chapter, Locke maintains that there is no more difficulty, if indeed so much, in the notion of immaterial spirit as of body. "Our idea of Body, as I think, is an extended solid substance, capable of communicating motion by impulse; and our idea of our Soul, as an immaterial Spirit, is of a substance that thinks, and has a power of exciting motion in body by Will or Thought." (§ 22.) Now, it is "no more a contradiction that Thinking should exist separate and independent from Solidity, than it is a contradiction that Solidity should exist separate and independent from Thinking, they being both but simple ideas independent one from another. And, having as clear and distinct ideas in us of Thinking as of Solidity, I know not why we may not as well allow a thinking thing without solidity, that is immaterial, to exist, as a solid thing without thinking, that is matter, to exist; especially since it is no harder to conceive how Thinking should exist without Matter, than how Matter should think." (§ 32.)

In the Fourth Book (ch. iii., § 6), however, he gave great scandal by suggesting the possibility that Matter might think, that it was not much more repugnant to our conceptions that God might, if he pleased, "superadd to Matter a Faculty of Thinking, than that he should superadd to it another substance with a faculty of thinking." At the same time, he regarded it as no less than a contradiction to suppose that Matter, "which is evidently in its own nature void of sense and thought," should be the "eternal first thinking Being," or God Himself; and, in his First Letter to the Bishop of Worcester, he grants that in us (as distinguished from the lower animals) it is in the highest degree probable that the "thinking substance" is immaterial. Materialism, therefore, as ordinarily understood, is certainly no part of Locke's system.

In discussing the idea of Substance, Locke seems generally to be thinking more of Matter than Mind. But, in an early part of the Essay (Bk. II., ch. xiii., § 18), he very rightly begs those who talk so much of Substance "to consider whether applying it, as they do, to the infinite incomprehensible God, to finite Spirit, and to Body, it be in the same sense, and whether it stands for the same idea, when each of those three so different beings are called Substances." As applied respectively to Matter and to Mind (whether finite or infinite), it appears to me that the word Substance assumes a very different meaning, and that the absurdities which it is possible to fix on the distinction between Matter and its attributes by no means extend to the distinction between Mind and its operations. For an union of certain forces or powers affecting our organisms in certain ways seems to exhaust our conception of external objects (the notion of externality, I conceive, being quite independent of that of the Substrate "matter"), but no similar enumeration of mental acts and feelings seems adequately to take the place of that "Self," or "I," of which we regard these as merely phases and modifications. It would much conduce to clearness in philosophical discussions if, at least amongst those who admit the dualism of matter and mind, the word Substance, whenever applied to incorporeal objects, were replaced by the word Mind, and, whenever applied to corporeal objects, by the word Matter.

The Second Book closes, in the Fourth and subsequent editions, with a short but very interesting Chapter on the "Association of Ideas." The student of Mental Philosophy will find it instructive to compare this Chapter with the previous account given by Hobbes (Human Nature, ch. iv.; Leviathan, Pt. I., ch. iii.), and the subsequent account given by Hume (Human Nature, Pt. I., § 4; Essays on Human Understanding, § 3), of the same phenomena. Locke appears to have been the first author to use the exact2 expression "Association of Ideas," and it is curious to find in this chapter (§ 5) the word "inseparable," so familiar to the readers of recent works on psychology, already applied to designate certain kinds of association. Some ideas, indeed, have, he says, a natural correspondence, but others, that "in themselves are not at all of kin," "come to be so united in some men's minds that one no sooner at any time comes into the understanding than the whole Gang, always inseparable, show themselves together."

The following passage on what may be called the associations of antipathy affords a good instance of Locke's power of homely and apposite illustration:

"Many children imputing the pain they endured at school to their books they were corrected for, so join those ideas together, that a book becomes their aversion, and they are never reconciled to the study and use of them all their lives after; and thus reading becomes a torment to them, which otherwise possibly they might have made the great pleasure of their lives. There are rooms convenient enough, that some men cannot study in, and fashions of vessels, which though never so clean and commodious, they cannot drink out of, and that by reason of some accidental ideas which are annexed to them and make them offensive. And who is there that hath not observed some man to flag at the appearance or in the company of some certain person not otherwise superior to him, but because, having once on some occasion got the ascendant, the idea of authority and distance goes along with that of the person, and he that has been thus subjected is not able to separate them."

Had Locke's Essay ended with the Second Book, we should hardly have detected in it any incompleteness. It might have been regarded as an analytical work on the nature and origin of our ideas, or, in other words, on the elements of our knowledge. There are, however, a third and fourth book—the former treating "Of Words," the latter "Of Knowledge and Opinion." Locke's notion appears to have been that, after treating of "Ideas," mainly as regarded in themselves, it was desirable to consider them as combined in Judgments or Propositions, and to estimate the various degrees of assent which we give or ought to give to such judgments, when formed. The Fourth Book thus, to a certain extent, takes the place, and was probably designed to take the place, of the Logic of the Schools. "But," to quote Locke's own language in the Abstract of the Essay, "when I came a little nearer to consider the nature and manner of human knowledge, I found it had so much to do with propositions, and that words, either by custom or necessity, were so mixed with it, that it was impossible to discourse of knowledge with that clearness we should, without saying something first of words and language."

The last three Chapters of the Third Book are remarkable for their sound sense, and may still be read with the greatest advantage by all who wish to be put on their guard against the delusions produced by misleading or inadequate language—those "Idola Fori" which Bacon describes as the most troublesome of the phantoms which beset the mind in its search for truth. Some of the best and freshest of Locke's thoughts, indeed, are to be found in this book, and especially in the less technical parts of it.

The Fourth Book, under the head of Knowledge, treats of a great variety of interesting topics: of the nature of knowledge, its degrees, its extent, and reality; of the truth and certainty of Universal Propositions; of the logical axioms, or laws of thought; of the evidence for the existence of a God; of Faith and Reason; of the Degrees of Assent; of Enthusiasm; of Error. Into these attractive regions it is impossible that I can follow my author, but the reader who wishes to see examples of Locke's strong practical sense and, at the same time, to understand the popularity so soon and so constantly accorded to the Essay, should make acquaintance at least with the four chapters last named.

From the task of description I now pass to that of criticism, though this must be confined within still narrower limits than the former, and indeed, amongst the multiplicity of subjects which invite attention, I must confine myself to one only: the account of the ultimate origin of our knowledge, which forms the main subject of the Essay.

Locke, as we have seen, derived all our knowledge from Experience. But experience, with him, was simply the experience of the individual. In order to acquire this experience, it was indeed necessary that we should have certain "inherent faculties." But of these "faculties" he gives no other account than that God has "furnished" or "endued" us with them. Thus, the Deus ex machina was as much an acknowledged necessity in the philosophy of Locke, and was, in fact, almost as frequently invoked, as in that of his antagonists. Is there any natural account to be given of the way in which we come to have these "faculties," of the extraordinary facility we possess of acquiring simple and forming complex ideas, is a question which he appears never to have put to himself. Inquiries of this kind, however, we must recollect, were foreign to the men of his generation, and, in fact, have only recently become a recognized branch of mental philosophy. Hence it was that his system left so much unexplained. Not only the very circumstance that we have "inherent faculties" at all, but the wide differences of natural capacity which we observe between one man or race and another, and the very early period at which there spring up in the mind such notions as those of space, time, equality, causality, and the like, are amongst the many difficulties which Locke's theory, in its bare and unqualified form, fails satisfactorily to answer. It was thus comparatively easy for Kant to show that the problem of the origin of knowledge could not be left where Locke had left it; that our À posteriori experiences presuppose and are only intelligible through certain À priori perceptions and conceptions which the mind itself imposes upon them; or, to use more accurate language, through certain À priori elements in our perceptions and conceptions, which the mind contributes from itself. Thus the child appears, as soon as it is capable of recognizing any source of its impressions, to regard an object as situated in space, an event as happening in time, circumstances which have occurred together as likely to occur together again. But Kant's own account was defective in leaving this À priori element of our knowledge unexplained, or, at least, in attempting no explanation of it. The mind, according to him, is possessed of certain Forms and Categories, which shape and co-ordinate the impressions received from the external world, being as necessary to the acquisition of experience, as experience is necessary to eliciting them into consciousness. But here his analysis ends. He does not ask how the mind comes to be possessed of these Forms and Categories, nor does he satisfactorily determine the precise relation in which they stand to the empirical elements of knowledge. When studying his philosophy, we seem indeed to be once more receding to the mysterious region of Innate Ideas. But the mystery is removed at least several stages back, if we apply to the solution of these mental problems the principle of Heredity, which has recently been found so potent in clearing up many of the difficulties connected with external nature. What are the "Innate Ideas" of the older philosophers, or the Forms and Categories of Kant, but certain tendencies of the mind to group phenomena, the "fleeting objects of sense," under certain relations and regard them under certain aspects? And why should these tendencies be accounted for in any other way than that by which we are accustomed to account for the tendency of an animal or plant, belonging to any particular species, to exhibit, as it developes, the physical characteristics of the species to which it belongs? The existence of the various mental tendencies and aptitudes, so far as the individual is concerned, is, in fact, to be explained by the principle of hereditary transmission. But how have these tendencies and aptitudes come to be formed in the race? The most scientific answer is that which, following the analogy of the theory now so widely admitted with respect to the physical structure of animals and plants, assigns their formation to the continuous operation, through a long series of ages, of causes acting uniformly, or almost uniformly, in the same direction—in one word, of Evolution. This explanation may have its difficulties, but it is at any rate an attempt at a natural explanation where no other such attempt exists, and it has the merit of falling in with the explanations of corresponding phenomena now most generally accepted amongst scientific men in other departments of knowledge. According to this theory, there is both an À priori and an À posteriori element in our knowledge, or, to speak more accurately, there are both À priori and À posteriori conditions of our knowing, the À posteriori condition being, as in all systems, individual experience, the À priori condition being inherited mental aptitudes, which, as a rule, become more and more marked and persistent with each successive transmission. Now Locke lays stress simply upon the À posteriori condition, though he recognizes a certain kind of À priori condition in our "natural faculties," and the simple ideas furnished by reflecting on their operations. The very important condition, however, of inherited aptitudes facilitating the formation of certain general conceptions concurrently, or almost concurrently, with the presentation of individual experiences, did not occur to him as an element in the solution of the problem he had undertaken to answer, nor, in that stage of speculation, could it well have done so. His peculiar contribution to the task of solving this question consisted in his skilful and popular delineation of the À posteriori element in knowledge, and in his masterly exposure of the insufficiency of the account of the À priori element, as then commonly given. Locke's own theory was afterwards strained by Hume and Hartley, and still more by his professed followers in France, such as Condillac and HelvÉtius, till at last, in the opinion of most competent judges, it snapped asunder. Then, under the massive, though often partial and obscure, treatment of Kant, came the rehabilitation of the À priori side of knowledge. In recent times, mainly by aid of the light thrown on it from other branches of inquiry, a more thorough and scientific treatment of psychology has done much, as I conceive, towards completing and reconciling the two divergent theories which at one time seemed hopelessly to divide the world of philosophic thinkers. And yet, as it appears to me, the ultimate mystery which surrounds the beginnings of intellectual life on the globe has by no means been removed.

As closely connected with this general criticism of Locke's system, or rather as presenting the defects just criticised under another form, I may notice the tendency of the Essay to bring into undue prominence the passive receptivities of the Mind, and to ignore its activity and spontaneity. The metaphor of the tabula rasa, the sheet of "white paper," once admitted, exercises a warping influence over the whole work. The author is so busied with the variety of impressions from without, that he seems sometimes almost to ignore the reaction of the mind from within. And yet this one-sideness of Locke's conception of mind may easily be exaggerated. "When the Understanding is once stored with simple ideas, it has the power to repeat, compare, and unite them, even to an almost infinite variety, and so can make at pleasure new complex ideas." (Bk. II., ch. ii., § 2.) Moreover, amongst the simple ideas themselves are the ideas of Reflection, "being such as the mind gets by reflecting on its own operations." The system, in fact, assumes an almost ceaseless activity of mind, after the simple ideas of sensation have once entered it. But where it fails is in not recognizing that mental reaction which is essential to the formation of even the simple ideas of sensation themselves, as well as that spontaneous activity of mind which often seems to assert itself independently of the application of any stimulus from without. Here again a more scientific psychology than was possible in Locke's day comes to our aid, and shows, as is done by Mr. Bain and other recent writers, that the nerves, stored with energy, often discharge themselves of their own accord, and that movement is at least as much an original factor in animal life as is sensation, while sometimes it even precedes it in time. Had the constant interaction of mental activity and mental receptivity, producing a compound in which it is often almost impossible to disentangle the elements, been duly recognized by Locke, it would certainly have made his philosophy less simple, but it would have made it more true to facts. Physiology, however, was in his days in far too backward a state itself to throw much light upon Psychology. And the reaction against the prevailing doctrine of Innate Ideas naturally led to a system in which the influences of external circumstances, of education and habit, were exaggerated at the expense of the native powers, or as they might more appropriately be called the inherited aptitudes, and the spontaneous activity of the mind.

Here, tempting as it is to follow my author along the many tracks of psychological, metaphysical, and logical discussion which he always pursues with sagacity, candour, and good sense, if not always with the consistency and profundity which we should require from later writers, my criticism must necessarily end.

Before, however, finally dismissing the Essay, I must pause to ask what was the main work in the history of philosophy and thought which it accomplished. Many of its individual doctrines, doubtless, could not now be defended against the attacks of hostile criticism, and some even of those which are true in the main, are inadequate or one-sided. But its excellence lies in its tone, its language, its method, its general drift, its multiplicity of topics, the direction which it gave to the thoughts and studies of reflecting men for many generations subsequent to its appearance. Of the tone of candour and open-mindedness which pervades it, of the unscholastic and agreeable form in which it is written, and of the great variety of interesting topics which it starts, I have spoken already. Its method, though not absolutely new, even in modern times, for it is at least, to some extent, the method of Descartes, if not, in a smaller degree, of Hobbes and Gassendi, was still not common at the time of its appearance. Instead of stating a series of preconceived opinions, or of dogmas borrowed from some dominant school, in a systematic form, Locke sets to work to examine the structure of his own mind, and to analyze into their elements the ideas which he finds there. This, the introspective method, as it has been called, though undoubtedly imperfect, for it requires to be supplemented by the study of the minds of other men, if not of the lower animals, as made known by their acts, and words, and history, is yet a great advance on the purely À priori, and often fanciful, methods which preceded it. Nor do we fail to find in the Essay some employment of that comparative method to which I have just alluded: witness the constant references to children and savages in the first book, and the stress which is laid on the variety of moral sentiment existing amongst mankind. This inductive treatment of philosophical problems, mainly introspective, but in some measure also comparative, which was extremely rare in Locke's time, became almost universal afterwards. Closely connected with the method of the book is its general purport. By turning the mind inwards upon itself, and "making it its own object," Locke surmises that all its ideas come either from without or from experience of its own operations. He finds, on examination and analysis, no ideas which cannot be referred to one or other of these two sources. The single word "experience" includes them both, and furnishes us with a good expression for marking the general drift of his philosophy. It was pre-eminently a philosophy of experience, both in its method and in its results. It accepts nothing on authority, no foregone conclusions, no data from other sciences. It digs, as it were, into the mind, detaches the ore, analyzes it, and asks how the various constituents came there. The analytical and psychological direction thus given to philosophy by Locke was followed by most of the philosophical writers of the eighteenth century. However divergent in other respects, Hume and Berkeley, Hartley and Reid, the French Sensationalists, Kant, all commence their investigations by inquiring into the constitution, the capacities, and the limits of the Human Mind. Nor can any system of speculation be constructed on a sound basis which has neglected to dig about the foundations of human knowledge, to ascertain what our thoughts can and what they cannot compass, and what are the varying degrees of assurance with which the various classes of propositions may be accepted by us. Two cautions, indeed, are necessary in applying this procedure. We must never forget that the mind is constantly in contact with external nature, and that therefore a constant action and reaction is taking place between them; and we must never omit to base our inductions on an examination of other minds as well as our own, bringing into the account, as far as possible, every type and grade of mental development.

It was not, however, only its general spirit and direction which Locke impressed on the philosophy of the eighteenth century. He may almost be said to have recreated that philosophy. There is hardly a single French or English writer (and we may add Kant) down to the time of Dugald Stewart, or even of Cousin, Hamilton, and J.S. Mill, who does not profess either to develope Locke's system, or to supplement, or to criticise it. Followers, antagonists, and critics alike seem to assume on the part of the reader a knowledge of the Essay on the Human Understanding, and to make that the starting-point of their own speculations. The office which Bacon assigns to himself with reference to knowledge generally might well have been claimed by Locke with reference to the science of mind. Both of them did far more than merely play the part of a herald, but of both alike it was emphatically true that they "rang the bell to call the other wits together."