A man conceives objects, like houses and trees, as existing when he does not actually see or touch them, just as much as when he does see or touch them. He conceives them as existing independent of any actual sensations of his own: and he proceeds to describe them as independent altogether of himself as a Subject--or as absolute, not relative, existences. But this distinction, though just as applied in ordinary usage, becomes inadmissable when brought to contradict the Protagorean doctrine; because the speaker professes to exclude, what cannot be excluded, himself as concipient Subject.[26] It is he who conceives absent objects as real and existing, though he neither sees nor touches them: he believes fully, that if he were in a certain position near them, he would experience those appropriate sensations of sight and touch, whereby they are identified. Though he eliminates himself as a _percipient_, he cannot eliminate himself as a _concipient_: _i.e._, as conceiving and believing. He can conceive no object without being himself the Subject conceiving, nor believe in any future contingency without being himself the Subject believing. He may part company with himself as percipient, but he cannot part company with himself altogether. His conception of an absent external object, therefore, when fully and accurately described, does not contradict the Protagorean doctrine. But it is far the most plausible objection which can be brought against that doctrine, and it is an objection deduced from the facts or cognitions of sense. [Footnote 26: Bishop Berkeley observes:-- "But, say you, surely there is nothing easier than 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, more than framing in your mind certain ideas which you call _books_ and _trees_, and 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 shows you have the power of imagining or forming ideas in your mind: but it doth not show 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 doth conceive bodies existing unthought of or without the mind, though at the same time they are apprehended by or exist in itself._" Berkeley, Principles of Human Knowledge, sect. xxiii. p. 34, ed. of Berkeley's Works, 1820. The same argument is enforced in Berkeley's First Dialogue between Hylas and Philonous, pp. 145-146 of the same volume.