The real physical world thus turns out to be, for Locke, very different in nature from how we often naïvely suppose it to be. A kind of veil interposes itself between our human sensory awareness of the world on the one hand, and, on the other, the world as it ‘really is’ – the world of corpuscular physics consisting simply of solid, extended, moving particles. Some readers may feel that this distinction between appearance and reality is indeed forced on us by the discoveries of science. But we need to be on our guard. Does science actually show us that a marigold is not ‘really’ coloured? Indeed, on Locke’s own account, if the redness of a rose is a ‘power’ to produce certain sensations in us, does this not imply that the flower does genuinely possess that power? Finally if a metaphysical veil is to be drawn between some of our ideas and how things really are ‘out there’, one might begin to ask whether any of our ideas can support the notion of ‘what really exists in the bodies themselves’ (for more on this, see extract 6, below).
To discover the nature of our ideas the better, and to discourse of them intelligibly, it will be convenient to distinguish them, as they are ideas or perceptions in our minds, and as they are modifications of matter in the bodies that cause such perceptions in us; that so we may not think (as perhaps usually is done) that they are exactly the images and resemblances of something inherent in the subject; most of those [ideas] of sensation being in the mind no more the likeness of something existing without [outside] us, than the names, that stand for them, are the likeness of our ideas, which yet upon hearing, they are apt to excite in us.
Whatsoever the mind perceives in itself, or is the immediate object of perception, thought, or understanding, that I call idea; and the power to produce any idea in our mind, I call quality of the subject wherein that power is. Thus a snowball having the power to produce in us the ideas of white, cold, and round, the powers to produce those ideas in us, as they are in the snowball, I call qualities; and as they are sensations, or perceptions, in our understandings, I call them ideas. Which ideas, if I speak of sometimes as in the things themselves, I would be understood to mean those qualities in the objects which produce them in us.
Qualities thus considered in bodies are, first such as are utterly inseparable from the body, in what estate soever it be; such as in all the alterations and changes it suffers, all the force can be used upon it, it constantly keeps; and such as sense constantly finds in every particle of matter, which has bulk enough to be perceived, and the mind finds inseparable from every particle of matter, though less than to make itself singly be perceived by our senses. E.g., take a grain of wheat, divide it into two parts, each part has still solidity, extension, figure, and mobility; divide it again, and it retains still the same qualities; and so divide it on, till the parts become insensible, they must retain still each of them all those qualities. For division (which is all that a mill, or pestle, or any other body, does upon another, in reducing it to insensible parts) can never take away either solidity, extension, figure, or mobility from any body, but only makes two, or more distinct separate masses of matter, of that which was but one before, all which distinct masses, reckoned as so many distinct bodies, after division make a certain number. These I call original or primary qualities of body, which I think we may observe to produce simple ideas in us, viz. solidity, extension, figure, motion, or rest, and number.
Secondly, such qualities, which in truth are nothing in the objects themselves, but powers to produce various sensations in us by their primary qualities, i.e. by the bulk, figure, texture, and motion of their insensible parts, as colours, sounds, tastes, etc., these I call secondary qualities. To these might be added a third sort which are allowed to be barely powers though they are as much real qualities in the subject, as those which I to comply with the common way of speaking call qualities, but for distinction secondary qualities. For the power in fire to produce a new colour, or consistency in wax or clay by its primary qualities, is as much a quality in fire, as the power it has to produce in me a new idea or sensation of warmth or burning, which I felt not before, by the same primary qualities, viz. the bulk, texture, and motion of its insensible parts.
The next thing to be considered, is how bodies produce ideas in us, and that is manifestly by impulse, the only way which we can conceive bodies operate in.
If then external objects be not united to our minds, when they produce ideas in it; and yet we perceive these original qualities in such of them as singly fall under our senses, it is evident, that some motion must be thence continued by our nerves, or animal spirits,3 by some parts of our bodies, to the brains or the seat of sensation, there to produce in our minds the particular ideas we have of them. And since the extension, figure, number, and motion of bodies of an observable bigness, may be perceived at a distance by the sight, it is evident some singly imperceptible bodies must come from them to the eyes, and thereby convey to the brain some motion, which produces these ideas, which we have of them in us.
After the same manner that the ideas of these original qualities are produced in us, we may conceive that the ideas of secondary qualities are also produced, viz. by the operation of insensible particles on our senses. For it [is] manifest that there are bodies, and good store of bodies, each whereof is so small that we cannot, by any of our senses, discover either their bulk, figure, or motion, as is evident in the particles of the air and water, and others extremely smaller than those – perhaps as much smaller than the particles of air, or water, as the particles of air or water are smaller than peas or hailstones. Let us suppose at present that the different motions and figures, bulk, and number of such particles, affecting the several organs of our senses, produce in us those different sensations which we have from the colours and smells of bodies; e.g. that a violet, by the impulse of such insensible particles of matter of peculiar figures and bulks, and in different degrees and modifications of their motions, causes the ideas of the blue colour, and sweet scent of that flower to be produced in our minds – it being no more impossible to conceive, that God should annex such ideas to such motions, with which they have no similitude, than that he should annex the idea of pain to the motion of a piece of steel dividing our flesh, with which that idea has no resemblance.
What I have said concerning colours and smells may be understood also of tastes and sounds, and other [similar] sensible qualities; which, whatever reality we, by mistake, attribute to them, are in truth nothing in the objects themselves but powers to produce various sensations in us, and depend on those primary qualities, viz. bulk, figure, texture, and motion of parts; as I have said.
From whence I think it is easy to draw this observation, that the ideas of primary qualities of bodies are resemblances of them, and their patterns do really exist in the bodies themselves; but 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. They are, in the bodies we denominate from them, only a power to produce those sensations in us. And what is sweet, blue, or warm in idea is but the certain bulk, figure, and motion of the insensible parts in the bodies themselves, which we call so.
Flame is denominated hot and light; snow white and cold and manna white and sweet, from the ideas they produce in us. Which qualities are commonly thought to be the same in those bodies that those ideas are in us, the one