and raised to the rank of universal conceptions of the genera to which they belong.

The simple ideas being the elements of the complex ones, he reduces complex ideas to three classes, namely, modes, substances, and relations. Modes are complex ideas but not involving existence by themselves, being merely modifications of simple ideas when their elements are similar, and mixed modes or modifications when their elements are dissimilar. Ideas of substances are those combinations of simple ideas employed to represent things existing by themselves. The ideas of relation arise from the comparison of one idea with another. To the purely modal ideas belong the mental modifications of space, time, thought, power, and other abstract conceptions. Our own experience and observation of the constant change of ideas in the mind, partly depending on the impressions of external objects, and partly on our own choice, soon leads the understanding to the conclusion that the same changes as have already been observed will continue to take place in the same objects through the same causes; accordingly, the understanding conceives in one thing or object a liability to change its form, and in another, the possibility of being the agent of that change, and thus the mind attains the idea of a power. Thus the clearest idea of power is derived from observing the activities of our own minds, as internal experience teaches us that by a mere volition we can set in motion parts of the body which were before at rest. If a substance possessing a power manifests it by an action, it is called a cause; and that which it brings to pass is called its effect. A cause is that through which something else begins to be; an effect is that which depends for its existence on something besides itself. The idea of substance itself contains nothing but the supposition of an unknown something serving as a support for qualities; we have no clear idea of it. Nor is our idea of material substance more distinct than our idea of spiritual substance. There is no reason for assuming that a spiritual substance cannot exist; we have no

more reason to doubt or deny the existence of spirits, than we have to deny the existence of bodies.59

He treats at length of relations, including that of cause and effect, of identity and diversity, of clear and distinct, obscure and confused ideas, of adequate and inadequate ideas, of real and fanatical ideas, of true and false ideas. Strictly speaking, truth and falsehood belong only to propositions; but ideas are sometimes termed true or false, though when so styled, there is some tacit proposition assumed; as ideas are but bare perceptions in our own minds, and cannot in themselves be said to be true or false. Any idea which we have in our minds, whether it accords or not with the existence of things, or with any ideas in the minds of other men, cannot properly for this alone be called false. But an idea is false when formed of inconsistent qualities or elements, or when it is judged to contain in it the real essence of any existing body, whereas it only contains a few of these; or again, when the mind judges its own idea to be the same as it is in other men's minds, signified by the

59 Locke in his treatment of the term substance the term which plays so great a part in the systems of Descartes and Spinoza-plainly admits his impotence. He says, "If anyone 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 anyone 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 inheres in," he would be in much the same plight as the Indian was who supported the world on the broad-backed tortoise. "And thus here, as in all other cases where we use words without having clear and distinct ideas, we talk like children. . The idea then we have, to which we give the general name substance, being nothing but the supposed, but unknown support of those qualities we find existing, which we imagine cannot subsist without something to support them, we call that support, substantia, which means in plain English, standing under, or upholding."—Ch. XXIII., Sect. 2. But again, in comparing our ideas of spirit and of body, he says, "In short, the idea we have of spirit, compared with the idea we have of body, stands thus: the substance of spirit is unknown to us; and so is the substance of body equally unknown to us."—Ibid., Sect. 30. An idea of substance in itself, that is, apart from any qualities in relation to our minds, is utterly barren; as we only conceive it as inconceivable-as nothing at all.

same word, when in fact it is not the same. He closes the Second Book with a short and interesting chapter on the " Association of Ideas". He was among the first to use this expression, which is now so familiar to all students of psychology.

In the Third Book, Locke treats on language at length, as the medium of stating and expressing our ideas and thoughts. Words are signs and marks which are necessary for communication, general terms and names of our ideas, considered as aids to the acquisition of knowledge, and for recording and communicating our thoughts. This part of the work is valuable, and contains some of Locke's best thoughts.60

The Fourth Book treats of knowledge and opinion, and extends to twenty-one chapters, in which many important and interesting matters are handled with great candour and ability. Such are the degrees, the limits, and the reality of our knowledge, of truth, universal propositions, maxims, the existence of God; the improvement of our knowledge, probability, and the degrees of assent; reason, faith and reason, and the causes of error.

According to Locke, knowledge is the perception of the agreement or disagreement of our ideas; this agreement being fourfold, namely, identity or diversity, relation, coexistence or necessary connection, and real existence. He explains these kinds of knowledge and relations of ideas at length, and proceeds to show that we know our own existence, and the existence of God. His reasoning and arguments to prove the existence of God are founded on the principle of mediate inference, the only method which his system of the mind permitted; but on this ground he argues well and wisely.

Locke discusses the provinces of faith and reason, and

60 He sums up his view of general terms in the following sentence:—“ All the great business of genera and species, and their essences, amounts to no more but this, that men, making abstract ideas, and settling them in their minds, with names annexed to them, do thereby enable themselves to consider things, and to discourse of them, as it were in bundles, for the easier and readier improvement and communication of their knowledge; which would advance but slowly, were their words and thoughts confined only to particulars."—Ch. III., Sect. 30.

though faith in divine revelation transcends rational knowledge, nevertheless, nothing can be regarded as a revelation which directly contradicts well ascertained and distinct rational knowledge.61

In the discussion of the limits of human knowledge, though he makes many true and sagacious statements, yet it is here, perhaps, that his main inconsistency culminates. Notwithstanding his doctrine that we have only an obscure and relative idea of substance, he adopted and expounded the distinction between the primary and the secondary qualities of bodies, describing the primary qualities as those which are inseparable from the conception of body. The primary qualities are really in bodies, whether our senses perceive them or not, and when we do perceive primary qualities, our ideas of them are resemblances of qualities really existing in these bodies. His own words are, "that the ideas of primary qualities of bodies are resemblances of them, and their patterns do really exist in the bodies themselves". While, on the other hand, "the ideas produced in us by these secondary qualities have no resemblance of them at all. There is nothing like our ideas existing in the bodies themselves." Thus it seems we know primary qualities, not simply as manifested to us, but as they exist in themselves; thus too the primary qualities of bodies must be independent of the human mind. Hence when he came to treat of the limits of knowledge, no necessary connection between the primary and the secondary qualities could be discovered; because the ideas obtained through the primary qualities of bodies were entirely different from the ideas obtained through the secondary qualities, there was no common root among these ideas for comparison, and consequently no knowledge. There was no science of bodies, or definite physics: "because we want perfect and adequate ideas of those very bodies which are nearest to us, and most under our command. Those which we have ranked into classes under names, and we think ourselves best ac

61 Ch. XVIII.

quainted with, we have but very imperfect and incomplete

ideas of body." 62

.

adequate ideas, I suspect, we have not of any Here the door was opened for the scepticism which Hume deduced from the principles of Locke's Essay.

Although we have now a more scientific psychology than was possible in Locke's day, nevertheless, his "Essay concerning Human Understanding" is a great monument of his genius, and one of the most interesting works in this department of literature. Its merit consists in its method, its general scope, its vast variety of topics, and the spirit of candour which pervades it. It has had a wide and remarkable influence on subsequent speculation, and on psychology, though at first it met with opposition in various quarters.

At any given time, the causes favourable to the success of a novel line of thought are various and complicated, and without at all pretending to exhaust them, we may indicate some of the conditions which conduced to the acceptance of Locke's philo

62 Book II., Ch. VIII.; Book IV., Ch. III. In treating on the limits of our knowledge, Locke says:-" He that knows anything, knows this in the first place, that he need not seek long for instances of his ignorance. The meanest and most obvious things that come in our way have dark sides, that the quickest sight cannot penetrate into. The clearest and most enlarged understandings of thinking men find themselves puzzled, and at a loss, in every particle of matter. We shall the less wonder to find it so when we consider the causes of our ignorance, which, I suppose, will be found to be chiefly these three:-1. Want of ideas; 2. Want of discoverable connection between the ideas we have; 3. Want of tracing and examining our ideas."-Ibid., Ch. III., Sect. 22.

I have not space to speak of Locke's other writings, and restrict myself to a few words on his ethical doctrines. He maintained that morality is solely based on the Will of God, and that what is most conducive to the public welfare is to be regarded as the expression of the Divine Will. Each man is required by the Divine Law to do all the good and prevent all the evil that he can; and good and evil being resolved into pleasure and pain, the ultimate test of moral conduct is its tendency to promote the pleasures and to avert the pains of mankind. Bk. I., Ch. III., Sect. 6; Bk. II., Ch. XXVIII.

Locke also maintained that morality is a science which can be demonstrated as clearly as mathematics. Bk. IV., Ch. III., Sect. 18; Ch. IV., Sect. 7; Ch. XII., Sect. 8.

Touching the will, he held that though a man is free to act, the will itself is always determined by motives: this theory is usually called determinism. Bk. II., Ch. XXI.