Do you say that in that case the tables and chairs must be supposed to disappear the moment we all leave the room? It is true that we do commonly think of the tables and chairs as remaining, even when there is no one there to see or touch them. But that only means, Berkeley explains, that if we or any one else were to come back into the room, we should perceive them. Moreover, even in thinking of them as things which might be perceived under certain conditions, they have entered our minds and so proclaimed their ideal or mind-implying character. To prove that things exist without the mind we should have to conceive of things as unconceived or unthought of. And that is a feat which no one has ever yet succeeded in accomplishing. Here is Berkeley's own answer to the objection: 'But, say you, surely there is nothing easier than for me to imagine trees, for instance, in a park, or books existing in a closet, and nobody by to perceive them. I answer, you may so, there is no difficulty in it; but what is all this, I beseech you, more than framing in your mind certain ideas which you call books and trees, and {15} at the same time omitting to frame the idea of any one that may perceive them? But do not you yourself perceive or think of them all the while? This therefore is nothing to the purpose: it only shews you have the power of imagining or forming ideas in your mind; but it does not shew that you can conceive it possible the objects of your thought may exist without the mind. To make out this, it is necessary that _you_ conceive them existing unconceived or unthought of, which is a manifest repugnancy. When we do our utmost to conceive the existence of external bodies, we are all the while only contemplating our own ideas. But the mind, _taking no notice of itself_, is deluded to think it can and does conceive bodies existing unthought of or without the mind, though at the same time they are apprehended by, or exist in, itself. A little attention will discover to any one the truth and evidence of what is here said, and make it unnecessary to insist on any other proofs against the existence of _material substance_.'[5]