BOOK II. creatures, but in the different parts of the same plant, fruit, or animal. The same may be said of colours and sounds. CHAP. III. I shall, therefore, in the account of simple ideas I am here giving, content myself to set down only such as are most material to our present purpose, or are in themselves less apt to be taken notice of though they are very frequently the ingredients of our complex ideas; amongst which, I think, I may well account solidity, which therefore I shall treat of in the next chapter. 1 An exhaustive enumeration of the one which plays the most important part among our complex ideas of bodies, especially as body is distinguished from pure space, and also in a criticism of the Cartesian analysis of matter. CHAPTER IV. IDEA OF SOLIDITY. 1. THE idea of solidity we receive by our touch: and it BOOK II. arises from the resistance which we find in body to the CHAP. IV. entrance of any other body into the place it possesses, We retill it has left it. There is no idea which we receive more ceive this Idea from constantly from sensation than solidity. Whether we move Touch. or rest, in what posture soever we are, we always feel something under us that supports us, and hinders our further sinking downwards; and the bodies which we daily handle make us percieve that, whilst they remain between them, they do, by an insurmountable force, hinder the approach of the parts of our hands that press them. That which thus hinders the approach of two bodies, when they are moved one towards another, I call solidity. I will not dispute whether this acceptation of the word solid be nearer to its original signification than that which mathematicians use it in. It suffices that I think the common notion of solidity will allow, if not justify, this use of it; but if any one think it better to call it impenetrability, he has my consent. Only I have thought the term solidity the more proper to express this idea, not only because of its vulgar use in that sense, but also because it carries something more of positive in it than impenetrability; which is negative, and is perhaps more a 1At bottom we get our distinct idea of solidity, according to Leibniz, through reason; although 'touch' provides reason with something which shows that solidity exists in nature. (See Nouv. Ess. Liv. ii. ch. 5.) According to the Essay, the idea arises from the feeling of resistance, and the motor sensations that are included vaguely CHAP. IV. BOOK II. consequence of solidity, than solidity itself1. This, of all other, seems the idea most intimately connected with, and essential to body; so as nowhere else to be found or imagined, but only in matter. And though our senses take no notice of it, but in masses of matter, of a bulk sufficient to cause a sensation in us: yet the mind, having once got this idea from such grosser sensible bodies, traces it further, and considers it, as well as figure, in the minutest particle of matter that can exist; and finds it inseparably inherent in body, wherever or however modified. Solidity 2. This is the idea which belongs to body, whereby we fills Space. conceive it to fill space. The idea of which filling of space is, that where we imagine any space taken up by a solid substance, we conceive it so to possess it, that it excludes all other solid substances; and will for ever hinder any other two bodies, that move towards one another in a straight line, from coming to touch one another, unless it removes from between them in a line not parallel to that which they move in 2. This idea of it, the bodies which we ordinarily handle sufficiently furnish us with. 1 Solidity, here defined by Locke, and afterwards (ch. viii) included in his list of the primary or real qualities of matter, is an ambiguous term, used in various meanings-geometrical and physical. 'The term solidity denotes, besides the absolute and necessary property of occupying space, simply, and in its two phases of Extension and Impenetrability, also the relative and contingent qualities of the Dense, the Inert, the Heavy, and the Hard.' (Hamilton.) With Locke it means the impenetrability, or ultimate incompres sibility, of matter-the impossibility by pressure of transforming an extended atom into something unextended. This impossibility is assumed to be permanent and absolute; but why thus assumed-whether on a priori or on experimental grounds-Locke does not inquire. At any rate, this necessary permanence is not å datum in the contingent experience of the sense of touch, whether regarded as the sense of simple contact, or including sense of muscular resistance; for sense is transitory, not absolute, in its revelations, and an intellectual impossibility of supposing a body that is not incompressible would refer the 'perception' to reason instead of sense. Moreover one can say that it is only as incompressible, because space-occupying, and obliged to resist the entrance of other bodies into its space, that what we call 'body' can be judged by us to exist at all. 2 This is to identify the idea of solidity, or the permanently and absolutely incompressible, with the idea of body, as something that is necessarily extended or space-occupying. In what follows Locke notes the distinction between the 'simple idea' of the solid and incompressible, and the idea of pure (empty) extension (§§ 3, 5); and between each of these CHAP. IV. 3. This resistance, whereby it keeps other bodies out of BOOK II. the space which it possesses, is so great, that no force, how great soever, can surmount it. All the bodies in the world, Distinct pressing a drop of water on all sides, will never be able to from Space. overcome the resistance which it will make, soft as it is, to their approaching one another, till it be removed out of their way: whereby our idea of solidity is distinguished both from pure space, which is capable neither of resistance nor motion; and from the ordinary idea of hardness. For a man may conceive two bodies at a distance, so as they may approach one another, without touching or displacing any solid thing, till their superficies come to meet; whereby, I think, we have the clear idea of space without solidity. For (not to go so far as annihilation of any particular body) I ask, whether a man cannot have the idea of the motion of one single body alone, without any other succeeding immediately into its place? I think it is evident he can: the idea of motion in one body no more including the idea of motion in another, than the idea of a square figure in one body includes the idea of a square figure in another. I do not ask, whether bodies do so exist, that the motion of one body cannot really be without the motion of another. To determine this either way, is to beg the question for or against a vacuum. But my question is,-whether one cannot have the idea of one body moved, whilst others are at rest? And I think this no one will deny. If so, then the place it deserted gives us the idea of pure space without solidity; whereinto any other body may enter, without either resistance or protrusion of anything. When the sucker in a pump is drawn, the space it filled in the tube is certainly the same whether any other body follows the motion of the sucker or not: nor does it imply a contradiction that, upon the motion of one body, another that is only contiguous to it should not follow it. The necessity of such a motion is built only on the supposition that the world is full; but not on the distinct ideas of space and solidity, which are as different as resistance and not resistance, protrusion and not protrusion. and the idea of hardness, i.e. resistance, firm but variable, on the part of an aggregate of atoms, to disintegration BOOK II. And that men have ideas of space without a body, their very disputes about a vacuum plainly demonstrate, as is shown in another place1. 1 CHAP. IV. From 4. Solidity is hereby also differenced from hardness, in that solidity consists in repletion, and so an utter exclusion of other bodies out of the space it possesses: but hardness, in a firm cohesion of the parts of matter, making up masses of a sensible bulk, so that the whole does not easily change its figure. And indeed, hard and soft are names that we give to things only in relation to the constitutions of our own bodics; that being generally called hard by us, which will put us to pain sooner than change figure by the pressure of any part of our bodies; and that, on the contrary, soft, which changes the situation of its parts upon an easy and unpainful touch 2. But this difficulty of changing the situation of the sensible parts amongst themselves, or of the figure of the whole, gives no more solidity to the hardest body in the world than to the softest; nor is an adamant one jot more solid than water. For, though the two flat sides of two pieces of marble will more easily approach each other, between which there is nothing but water or air, than if there be a diamond between them; yet it is not that the parts of the diamond are more solid than those of water, or resist more; but because the parts of water, being more easily separable from each other, they will, by a side motion, be more easily removed, and give way to the approach of the two pieces of marble. But if they could be kept from making place by that side motion, they would eternally hinder the approach of these two pieces of marble, as much as the diamond; and it would be as impossible by any force to surmount their resistance, as to surmount the resistance of the parts of a diamond. The softest body in the world will as invincibly resist the 1 Ch. xiii. §§ 21-23. 3 2 In this the hardness is contrasted with the solidity, impenetrability, and compressibility of matter, which Locke takes to be not relative to our sensations but necessary to its existence. * Mere sense, which, in strictness, is only of the present, cannot reveal what is eternally necessary, and so cannot reveal what Locke finds in the idea of solidity. |