And as with the secondary qualities of matter, so, on the same showing, must it be with the primary. If colour, taste, scent, and the like, exist nowhere but in the mind, so neither do extension, solidity, and the like. If the former could not exist unless there were intelligent minds to perceive them, then neither could the latter. For, by extension and its cognates, we understand simply relations which we conceive to exist between certain qualities of objects identical with certain of our own visual and tactile sensations, or between these and our consciousness of muscular effort; but inasmuch as all sensations and all consciousness are purely mental, and exist nowhere but in the mind, it follows necessarily that ideas of relation between different sensations, or between sensations and consciousness, must also be purely mental, and non-existent save in the mind. All the qualities of matter, therefore, primary as well as secondary, are alike conceptions of the mind, and consequently could not exist without a mind for them to be conceived by and to exist in. But if the qualities did not exist, then matter, which cannot be conceived otherwise than as an assemblage of qualities, could not exist either. Wherefore in respect of matter itself, as well as of the qualities of matter, _esse_ is _percipi_, essence is perception, to be is to be perceived. Wherefore, finally, if there were no mind to perceive matter, matter could not exist. Q. E. D.[33] Although in the foregoing summary of an argument to which not Berkeley and Huxley alone, but others of the deepest and acutest thinkers that this country has produced, have contributed, I have strenuously laboured to state all its points as convincingly as the obligations of brevity would permit, I am not myself by any means convinced by it. On the contrary, although to say so may seem to imply a considerable overstock of modest assurance, still I do say that whatever portion of it is sound is irrelevant, and that whatever portion is relevant is not sound. So much of it as relates to the nature of the qualities of matter, is, however interesting or otherwise important, very little, if at all, to the purpose. No doubt if I prick my finger with a needle, or--to take in preference an illustration employed by Locke--if my fingers ache in consequence of my handling snow, it would be supremely ridiculous to talk of the pain I feel being in the snow; yet not a whit more ridiculous than to call the snow itself white or cold, if, by so speaking, I mean that anything in the slightest degree resembling my sensation of either snowy whiteness or snowy coldness resides in the snow itself. And as of coldness and whiteness, so of all the other so-styled secondary qualities. If I smell a rose, or listen to a piano, the rose or the piano is quite insensible to the scent or sounds by which my sense is ravished. And of primary qualities, also, precisely the same thing may with equal confidence be alleged. A stone which I