‘15. In short, let any one consider those arguments which are thought manifestly to prove that colours, tastes, &c. exist only in the mind, and he will find they may with equal force be brought to prove the same thing of extension, figure, and motion. Though it must be confessed this method of arguing does not so much prove that there is no extension, colour, &c. in an outward object, as that we do not know by sense which is the true extension or colour of the object. But the foregoing arguments plainly show it to be impossible that any colour or extension at all, or other sensible quality whatsoever, should exist in an unthinking subject without the mind, or in truth, that there should be any such thing as an outward object.’—_Principles of Human Knowledge_, pp. 54, &c. Again, he says, page 58:— ‘But though it were possible that solid, figured movable substances may exist without the mind, corresponding to the ideas we have of bodies, yet how is it possible for us to know this? Either we must know it by sense or by reason. As for our senses, by them we have the knowledge only of our sensations, ideas, or those things that are immediately perceived by sense, call them what you will; but they do not inform us that things exist without the mind, or unperceived, like to those which are perceived. This the materialists themselves acknowledge. It remains, therefore, that if we have any knowledge at all of external things, it must be by reason, inferring their existence from what is immediately perceived by sense. But I do not see what reason can induce us to believe the existence of bodies without the mind, from what we perceive, since the very patrons of matter themselves do not pretend there is any necessary connexion betwixt them and our ideas. I say it is granted on all hands (and what happens in dreams, frenzies, and the like, puts it beyond dispute) that it is possible we might be affected with all the ideas we have now, though there were no bodies existing without resembling them. Hence it is evident the supposition of external bodies is not necessary for the producing our ideas, since it is granted they are produced sometimes, and might possibly be produced always, in the same order we see them in at present, without their concurrence. But though we might possibly have all our sensations without them, yet perhaps it may be thought easier to conceive and explain the manner of their production, by supposing external bodies in their likeness rather than otherwise, and so it might be at least probable there are such things as bodies that excite their ideas in our minds. But neither can this be said, for though we give the materialists their external bodies, they, by their own confession, are never the nearer knowing how our ideas are produced, since they own themselves unable to comprehend in what manner body can act upon spirit, or how it is possible it should imprint any idea in the mind. Hence it is evident the production of