1. We receive this idea from touch. The idea of solidity we receive by our touch: and it arises from
the resistance which we find in body to the entrance of any other body into the place it possesses,
till it has left it. There is no idea which we receive more constantly from sensation than solidity.
Whether we move or rest, in what posture soever we are, we always feel something under us that
support us, and hinders our further sinking downwards; and the bodies which we daily handle make
us perceive 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 consequence of solidity, than solidity itself. 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.
2. Solidity fills space. This is the idea which belongs to body, whereby we 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. This idea of it, the bodies which we ordinarily handle sufficiently furnish us with.
3. Distinct from space. This resistance, whereby it keeps other bodies out of the space which it
possesses, is so great, that no force, how great soever, can surmount it. Al the bodies in the world,
pressing a drop of water on all sides, will never be able to 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
that men have ideas of space without a body, their very disputes about a vacuum plainly
demonstrate, as is shown in another place.
4. From hardness. 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 bodies; 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.
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 coming together of any other two
bodies, if it be not put out of the way, but remain between them, as the hardest that can be found or
imagined. He that shall fill a yielding soft body well with air or water, will quickly find its resistance.
And he that thinks that nothing but bodies that are hard can keep his hands from approaching one
another, may be pleased to make a trial, with the air inclosed in a football. The experiment, I have
been told, was made at Florence, with a hollow globe of gold filled with water, and exactly closed;
which further shows the solidity of so soft a body as water. For the golden globe thus filled, being
put into a press, which was driven by the extreme force of screws, the water made itself way through
the pores of that very close metal, and finding no room for a nearer approach of its particles within,
got to the outside, where it rose like a dew, and so fell in drops, before the sides of the globe could
be made to yield to the violent compression of the engine that squeezed it.
5. On solidity depend impulse, resistance, and protrusion. By this idea of solidity is the extension of
body distinguished from the extension of space:--the extension of body being nothing but the
cohesion or continuity of solid, separable, movable parts; and the extension of space, the continuity
of unsolid, inseparable, and immovable parts. Upon the solidity of bodies also depend their mutual
impulse, resistance, and protrusion. Of pure space then, and solidity, there are several (amongst
which I confess myself one) who persuade themselves they have clear and distinct ideas; and that
they can think on space, without anything in it that resists or is protruded by body. This is the idea of
pure space, which they think they have as clear as any idea they can have of the extension of body:
the idea of the distance between the opposite parts of a concave superficies being equally as clear
without as with the idea of any solid parts between: and on the other side, they persuade
themselves that they have, distinct from that of pure space, the idea of something that fills space,
that can be protruded by the impulse of other bodies, or resist their motion. If there be others that
have not these two ideas distinct, but confound them, and make but one of them, I know not how
men, who have the same idea under different names, or different ideas under the same name, can
in that case talk with one another; any more than a man who, not being blind or deaf, has distinct
ideas of the colour of scarlet and the sound of a trumpet, could discourse concerning scarlet colour
with the blind man I mentioned in another place, who fancied that the idea of scarlet was like the
sound of a trumpet.
6. What solidity is. If any one ask me, What this solidity is, I send him to his senses to inform him.
Let him put a flint or a football between his hands, and then endeavour to join them, and he will
know. If he thinks this not a sufficient explication of solidity, what it is, and wherein it consists; I
promise to tell him what it is, and wherein it consists, when he tells me what thinking is, or wherein it
consists; or explains to me what extension or motion is, which perhaps seems much easier. The
simple ideas we have, are such as experience teaches them us; but if, beyond that, we endeavour
by words to make them clearer in the mind, we shall succeed no better than if we went about to
clear up the darkness of a blind man's mind by talking; and to discourse into him the ideas of light
and colours. The reason of this I shall show in another place.