Lively ideas real, because they must be effects of things.
56. In short, with Locke the simple idea, the perception of existence corresponding to the idea, and the judgment of identity, are absolutely merged, and in mutual involution, sometimes under one designation, sometimes under another, are alike presented as the beginning of knowledge. As occasion requires, each does duty for the other. Thus, if the ‘reality of knowledge’ be in question, the simple idea, which is given, is treated as involving the perception of existence, and the reality is established. If in turn this perception is distinguished from the simple idea, and it is asked whether the correspondence between idea and existence is properly matter of knowledge, the simple idea has only to be treated as involving the judgment of identity, which again involves that of existence, and the question is answered. So in the context under consideration (Book IV. chap. ii. sec. 14), after raising the question as to the existence of a thing corresponding to the idea, he answers it by the counter question, ‘whether anyone is not invincibly conscious to himself of a different perception, when he looks on the sun by day, and thinks on it by night; when he actually tastes wormwood, or smells a rose, or only thinks on that savour or odour? We as plainly find the difference there is between any idea revived in our minds by our own memory, and actually coming into our minds by our senses, as we do between any two distinct ideas.’ The force of the above lies in its appeal to the perception of identity, or—to apply the language in which Locke describes this perception—the knowledge that the idea which a man calls the smell of a rose is the very idea it is. [1] The mere difference in liveliness between the present and the recalled idea, which, as Berkeley and Hume rightly maintained, is the only difference between them as mere ideas, cannot by itself constitute the difference between the knowledge of the presence of a thing answering to the idea and the knowledge of its absence. It can only do this if the more lively idea is identified with past lively ideas as a representation of one and the same thing which ‘agrees with itself’ in contrast to the multiplicity of the sensations, its signs. Only in virtue of this identification can either the liveliness of the idea show that the thing—the sun or the rose—is there, or the want of liveliness that it is not, for without it there would be no thing to be there or not to be there. It is because this identification is what Locke understands by the first sort of perception of agreement between ideas, and because he virtually finds this perception again in the simple idea, that the simple idea is to him the index of reality. But if so, the idea in its primitive simplicity is the sign of a thing that is ever the same in the same relations, and we find the ‘workmanship of the mind,’ its inventions of substance, cause, and relation, in the very rudiments of knowledge.
[1] See above, paragraph 25.
Present sensation gives knowledge of existence.
57. With that curious tendency to reduplication, which is one of his characteristics, Locke, after devoting a chapter to the ‘reality of human knowledge,’ of which the salient passage as to simple ideas has been already quoted, has another upon our ‘knowledge of existence.’ Here again it is the sensitive knowledge of things actually present to our senses, which with him is merely a synonym for the simple idea, that is the prime criterion. (Book IV. chap. iii. secs. 5 and 2, and chap. ii. sec. 2.) After speaking of the knowledge of our own being and of the existence of a God (about which more will be said below), he proceeds, ‘No particular man can know the existence of any other being, but only when, by actually operating upon him, it makes itself perceived by him. For the having the idea of anything in our mind no more proves the existence of that thing, than the picture of a man evidences his being in the world, or the visions of a dream make thereby a true history. It is therefore the actual receiving of ideas from without, that gives us notice of the existence of other things, and makes us know that something doth exist at that time without us, which causes that idea in us, though perhaps we neither know nor consider how it does it; for it takes not from the certainty of our senses and the ideas we receive by them, that we know not the manner wherein they are produced; e.g. whilst I write this, I have, by the paper affecting my eyes, that idea produced in my mind, which, whatever object causes, I call white; by which I know that the quality or accident (i.e. whose appearance before my eyes always causes that idea) doth really exist, and hath a being without me. And of this the greatest assurance. I can possibly have, and to which my faculties can attain, is the testimony of my eyes, which are the proper and sole judges of this thing, whose testimony I have reason to rely on, as so certain, that I can no more doubt whilst I write this, that I see white and black, and that something really exists that causes that sensation in me, than that I write and move my hand.’ (Book IV. chap. xi. secs. 1, 2.)
Reasons why its testimony must be trusted.
58. Reasons are afterwards given for the assurance that the ‘perceptions’ in question are produced in us by ‘exterior causes affecting our senses.’ The first (a) is, that ‘those that want the organs of any sense never can have the ideas belonging to that sense produced in their mind.’ The next (b), that whereas ‘if I turn my eyes at noon toward the sun, I cannot avoid the ideas which the light or the sun then produces in me;’ on the other hand, ‘when my eyes are shut or windows fast, as I can at pleasure recall to my mind the ideas of light or the sun, which former sensations had lodged in my memory, so I can at pleasure lay them by.’ Again (c), ‘many of those ideas are produced in us with pain which afterwards we remember without the least offence. Thus the pain of heat or cold, when the idea of it is revived in our minds, gives us no disturbance; which, when felt, was very troublesome, and is again, when actually repeated; which is occasioned by the disorder the external object causes in our body, when applied to it.’ Finally (d), ‘our senses in many cases bear witness to the truth of each other’s report, concerning the existence of sensible things without us. He that sees a fire may, if he doubt whether it be anything more than a bare fancy, feel it too.’ Then comes the conclusion, dangerously qualified: ‘When our senses do actually convey into our understandings any idea, we cannot but be satisfied that there doth something at that time really exist without us, which doth affect our senses, and by them give notice of itself to our apprehensive faculties, and actually produce that idea which we then perceive; and we cannot so far distrust their testimony as to doubt that such collections of simple ideas, as we have observed by our senses to be united together, actually exist together. But this knowledge extends as far as the present testimony of our senses, employed about particular objects, that do then affect them, and no farther. For if I saw such a collection of simple ideas as is wont to be called man, existing together one minute since, and am now alone; I cannot be certain that the same man exists now, since there is no necessary connexion of his existence a minute since with his existence now. By a thousand ways he may cease to be, since I had the testimony of my senses for his existence.’ (Book IV. chap. xi. sec. 9.)
How does this account fit Locke’s definition of knowledge?
59. Upon the ‘knowledge of the existence of things,’ thus established, it has to be remarked in the first place that, after all, according to Locke’s explicit statement, it is not properly knowledge. It is ‘an assurance that deserves the name of knowledge’ (Book IV. chap. ii. sec. 14, and xi. sec. 3), yet being neither itself an intuition of agreement between ideas, nor resoluble into a series of such intuitions, the definition of knowledge excludes it. Only if existence were itself an ‘idea,’ would the consciousness of the agreement of the idea with it be a case of knowledge; but to make existence an idea is to make the whole question about the agreement of ideas, as such, with existence, as such, unmeaning. To seek escape from this dilemma by calling the consciousness of the agreement in question an ‘assurance’ instead of knowledge is a mere verbal subterfuge. There can be no assurance of agreement between an idea and that which is no object of consciousness at all. If, however, existence is an object of consciousness, it can, according to Locke, be nothing but an idea, and the question as to the assurance of agreement is no less unmeaning than the question as to the knowledge of it. The raising of the question in fact, as Locke puts it, implies the impossibility of answering it. It cannot be raised with any significance, unless existence is external to and other than an idea. It cannot be answered unless existence is, or is given in, an object of consciousness, i.e. an idea.
Locke’s account of the testimony of sense renders his question as to its veracity superfluous.