On the problem above stated, which has been often made a subject of dispute, I shall only remark that the answer given to it, with which Mr. Locke agrees, is directly repugnant to his doctrine of the real existence of the primary qualities of matter, namely figure and extension. For it is plain, that if there is any thing in external objects answering to their ideas in our minds, the ideas we have of those qualities and which are conveyed by different senses, must be like one another. If the ideas of figure as a visible and tangible thing have no resemblance to themselves, it is ridiculous to suppose that they can coincide with any thing out of them in nature. Secondly, it appears to me that the mind must recognise a certain similarity between the impressions of different senses in this case. For instance, the sudden change or discontinuity of the sensation, produced by the sharp angles of the cube, is something common to both ideas, and if so, must afford a means of comparing them together. Berkeley, in his ‘Essay on Vision,’ goes so far as to deny that there is any intuitive analogy between the ideas of number as conveyed by different senses, and asserts that the distinction between the two legs of a statue, for instance, as perceived by the touch or by the sight would not imply any idea of like or same. I grant this consequence to be true, on the principle maintained by him that there are no abstract ideas in the mind, for on this principle there can be no idea answering to the words same or different, but then this argument would destroy all kind of coincidence not only between ideas of different senses, but between repeated impressions of the same sense. The ‘Essay on Vision,’ of which I have already spoken, apparently originated in the problem here inserted, and is a more complete exemplification of the effects of association with respect to objects of sight than is to be found even in Hartley’s account of this subject.
Mr. Locke’s account of the distinction between wit and understanding I have already noticed; his explanation of the difference between idiots and madmen has been often referred to, and is as follows:
‘The defect in naturals seems to proceed from want of quickness, activity, and motion in the intellectual faculties, whereby they are deprived of reason: whereas madmen, on the other side, seem to suffer by the other extreme. For they do not appear to me to have lost the faculty of reasoning; but having joined together some ideas very wrongly, they mistake them for truths; and they err as men do that argue right from wrong principles: for, by the violence of their imaginations, having taken their fancies for realities, they make right deductions from them. Thus you shall find a distracted man, fancying himself a king, with a right inference require suitable attendance, respect, and obedience: others, who have thought themselves made of glass, have used the caution necessary to preserve such brittle bodies. Hence it comes to pass, that a man who is very sober, and of a right understanding in all other things, may in one particular be as frantic as any in Bedlam, if either by any sudden very strong impression, or long fixing his fancy upon one sort of thoughts, incoherent ideas have been cemented together so powerfully as to remain united. But there are degrees of madness, as of folly; the disorderly jumbling together of ideas is in some more, and some less. In short, herein seems to lie the difference between idiots and madmen: that madmen put wrong ideas together, and so make wrong propositions, but argue and reason right from them: but idiots make very few or no propositions, and reason scarce at all.’
Mr. Locke’s account of Liberty and Necessity, contained in his chapter ‘On Power,’ has been commented upon in the previous Essay. As is there remarked, it is one which has been more found fault with than any other part of his work, I think without reason. He seems evidently to have admitted the definition of necessity, but not the name, which is not much to be wondered at, considering the improper use to which it is liable, and which can scarce be separated from it in the closest reasoning, much less as a term of general signification: in other words, he denies the power of the mind to act without a cause or motive, or, in any manner, in any circumstances, from mere indifference and absolute self motion; but he at the same time denies the inference which has been drawn from this principle, that the mind is not an agent at all, but altogether subject to external force, or blind impulse.
Mr. Locke, in treating of complex ideas, divides them into three sorts, those of modes, substances, and relations.
First, ‘Modes,’ he says, ‘I call such complex ideas, which, however compounded, contain not in them the supposition of subsisting by themselves, but are considered as dependences on, or affections of substances: such are the ideas signified by the words triangle, gratitude, murder, &c. Of these modes there are two sorts. 1. There are some which are only variations or different combinations of the same simple idea, without the mixture of any other, as a dozen or score, which are nothing but the ideas of so many distinct units added together, and these I call simple modes. 2. There are others, compounded of simple ideas of several kinds put together, to make one complex one; e.g. beauty, consisting of a certain composition of colour and figure, causing delight in the beholder; theft, which being the concealed change of the possession of any thing, without the consent of the proprietor, contains, as is visible, a combination of several ideas of several kinds, and these I call mixed modes.’
With respect to modes, the author endeavours to shew, I think improperly, that as they are put together arbitrarily by the mind, according to circumstances, that they have no real existence in nature, and that the ideas we form of them are always correct. Neither of these consequences will be found to follow: i.e. the circumstances and actions which constitute theft do actually exist without the mind and are necessary to that idea, though it is arbitrary in me according to the occasion or the purpose in view, to think of that collection of ideas or another, which shall constitute robbery; that is, I may add or leave out the circumstance of violence, as it happens; secondly, I may, without being aware of it, add or leave out some circumstance necessary to the combination of ideas spoken of, and thus confuse one idea with another, and not merely miscal, as Mr. Locke supposes, but misconceive the mode in question. We then merely miscal when though we give a wrong name to a thing, the idea is kept perfectly distinct and clear from other ideas, otherwise we confound both names and things. But it will not be contended, that the ideas of theft, robbery, and fraud, for instance, are always kept clear in every one’s mind, so that he is at no loss ever to define them, or can immediately in all cases refer any action to the class to which it belongs. Every collection of ideas which the mind puts together is undoubtedly that collection and no other; but in forming the ideas of mixed modes, the mind does something more than this, or it supposes one collection of ideas to be the same as another which it has had at a former time, and gives a certain name to, and in this supposition it often errs.
On this subject, the author is a good deal puzzled with the question, how it is possible for the mind ever to confound one idea with another? It is indeed a puzzling question, but the answer which he gives to it in resolving it into a mistake of words, is very unsatisfactory. For there is no more reason why we should mistake one name or sign of an idea for another, than why we should mistake the ideas themselves. If every circumstance belonging to our ideas was necessarily clear and self-evident to the mind, the sign affixed to it, which is one of those circumstances, would be so too, and we find that in those things with which we have a thorough acquaintance, we never confound one name with another, or if we should, it does not disturb the idea, and is of no consequence.
Among the second sort of complex ideas Mr. Locke classes those of substances. These, he says, are such combinations of simple ideas as are taken to represent distinct, particular things, subsisting by themselves, in which the supposed or confused idea of substance, such as it is, is always the first or chief. Thus, if to substance be joined the simple idea of a certain dull whitish colour, with certain degrees of weight, hardness, ductility and fusibility, we have the idea of lead; and a combination of the ideas of a certain sort of figure, with the power of motion, thought, and reasoning, joined to substance, make the ordinary idea of a man. Now of substances also there are two sorts of ideas; one of single substances, as they exist separately, as of a man or a sheep; the other of several of those put together, as an army of men or a flock of sheep: which collective ideas of several substances are as much each of them one single idea as that of a man or an unit.’ He then adds, ‘and the third sort of complex ideas is that which we call relative, which consists in the consideration and comparing one idea with another.’ This last sort of ideas seems to me the only ones that are perfectly simple and indivisible: things themselves are always complex. Mr. Locke considers rightly that we know nothing of the nature of substance, and that we can only define it as an abstract idea of some thing, that supports accidents or connects different sensible qualities together. For this modest confession of his own ignorance he was however called to a very severe account by the learned of the time, Bishop Stillingfleet and others, who thought they knew more of the matter, and could penetrate the essence of things. The ‘Essay on the Human Understanding’ is swelled out with repeated and long extracts from this controversy, and they are not the least valuable part of the work, as they show to what shifts men can be driven, to defend systematically not truth but their own opinion, who become blind and obstinate by implicit faith, and who by adhering to every established prejudice drive others into all the absurdities of paradox.
Mr. Locke’s own account of our ideas of substance is a good deal spun out, and is enriched with as many illustrations from the qualities of gold, as if he had been candidate for the place of assay-master of the mint. The chapter ‘On Identity’ is perhaps the best reasoned and the most full of thought and observation of any in the Essay: though the author sets out with an observation which seems to augur differently. For after explaining identity as it relates to individuality, or implies that a thing is the same with itself, he says, ‘From what has been said it is easy to discover what is so much inquired after, the principium individuationis: and that, it is plain, is existence itself, which determines a being of any sort to a particular time and place, incommunicable to two beings of the same kind.’ He then, very wisely quitting this principle which would certainly be of no use to him, proceeds directly to account for the identity of different things from a continuance, not of the same substance, but of the same essence, or of the characteristic properties of any thing, carried on in succession; as a river is the same while it flows through the same channel, or an oak while it retains the same organization, and a man while he retains the same life and continued consciousness.