Once this principle has been accepted, all the other doctrines of the modern philosophy seem to follow by an easy inference:
Once we have removed sounds, colours, heat, cold, and other perceptible qualities from the category of continuous independent existents, we are left with only what are called ‘primary qualities’, as the only real ones of which we have any adequate notion. These primary qualities are extension and solidity, with their different mixtures and special cases: shape, motion, gravity, and cohesion. The generation, growth, decline, and death of animals and vegetables are noth- ing but changes of shape and motion, as are all the operations of bodies on each other, and the operations of fire, light, water, air, earth and all the elements and powers of Nature. One shape and motion produces another shape and motion; and we can’t form even the remotest idea of any force or drive (active or passive) among systems of matter other than that one.
I think that many objections could be made to this system, but at present I shall confine myself to one that I think is very decisive. I contend that instead of explaining the operations of external objects by means of this system, we utterly annihilate all these objects and reduce ourselves to the opinions of the most extravagant scepticism about them. If colours, sounds, tastes, and smells are merely perceptions, nothing that we can conceive has a real, continuous, and independent existence—not even motion, extension, and solidity, which are the primary qualities emphasized most ·in the modern philosophy·.