Principles Of Human Knowledge - pg. 109

But though it were possible that solid, figured, moveable 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 sense, by them we have the knowledge only of our sensations, ideas, or those thing 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 perceieved. 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 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 happened in dreams, phrensies, and the like, puts it beyond dispute) that it is possible we might be affected with all the ideas we have now, though no bodies existed without resembling them.