ust be non entities, unless conceived as coloured or solid.
Colour is excluded from any real existence. The reality, therefore, of
our idea of extension depends upon the reality of that of solidity, nor
can the former be just while the latter is chimerical. Let us, then,
lend our attention to the examination of the idea of solidity.

The idea of solidity is that of two objects, which being impelled by the
utmost force, cannot penetrate each other; but still maintain a
separate and distinct existence. Solidity, therefore, is perfectly
incomprehensible alone, and without the conception of some bodies, which
are solid, and maintain this separate and distinct existence. Now what
idea have we of these bodies? The ideas of colours, sounds, and other
secondary qualities are excluded. The idea of motion depends on that
of extension, and the idea of extension on that of solidity. It is
impossible, therefore, that the idea of solidity can depend on either of
them. For that would be to run in a circle, and make one idea depend on
another, while at the same time the latter depends on the former. Our
modern philosophy, therefore, leaves us no just nor satisfactory idea of
solidity; nor consequently of matter.

This argument will appear entirely conclusive to every one that
comprehends it; but because it may seem abstruse and intricate to the
generality of readers, I hope to be excused, if I endeavour to render
it more obvious by some variation of the expression. In order to form
an idea of solidity, we must conceive two bodies pressing on each other
without any penetration; and it is impossible to arrive at this idea,
when we confine ourselves to one object, much more without conceiving
any. Two non-entities cannot exclude each other from their places;
because they never possess any place, nor can be endowed with any
quality. Now I ask, what idea do we form of these bodies or objects,
to which we suppose solidity to belong? To say, that we conceive them
merely as solid, is to run on in infinitum. To affirm, that we paint
them out to ourselves as extended, either resolves all into a false
idea, or returns in a circle. Extension must necessarily be considered
either as coloured, which is a false idea; I or as solid, which
brings us back to the first question. We may make the same observation
concerning mobility and figure; and upon the whole must conclude, that
after the exclusion of colours, sounds, heat and cold from the rank of
ex