on either account forfeiting its identity. This view was taken for granted by Plato, but is elaborately defended in our own day. During the intervening period epistemology has been largely occupied with difficulties inherent in the representative theory, and from that discussion there has emerged the theory of _idealism_,[175:17] the great rival theory to that of realism. [Sidenote: The Relation of Knowledge to its Object According to Idealism.] § 70. The representative theory contains at least one obvious difficulty. If the thinker be confined to his ideas, and if the reality be at the same time beyond these ideas, how can he ever verify their report? Indeed, what can it mean that an idea should be true of that which belongs to a wholly different category? How under such circumstances can that which is a part of the idea be attributed with any certainty to the object? Once grant that you know only your ideas, and the object reduces to an unknown _x_, which you retain to account for the outward pointing or reference of the ideas, but which is not missed if neglected. The obvious though radical theory of idealism is almost inevitably the next step. Why assume that there is any object other than the state of mind, since all positive content belongs to that realm? The eighteenth century English philosopher, Bishop Berkeley, was accused by his contemporaries of wilful eccentricity, and even madness, for his boldness in accepting this argument and drawing this conclusion: "The table I write on I say exists; that is, I see and feel it: and if I were out of my study I should say it existed; meaning thereby that if I was in my study I might perceive it, or that some other spirit actually does perceive it. There was an odor--that is, it was smelt; there was a sound--that is, it was heard; a color or figure, and it was perceived by sight or touch. This is all that I can understand by these and the like expressions. For as to what is said of the _absolute_ existence of unthinking things, without any relation to their being perceived, that is to me perfectly unintelligible. Their _esse_ is _percipi_; nor is it possible that they should have any existence out of the minds or thinking thing which perceives them."[176:18] [Sidenote: Phenomenalism, Spiritualism, and Panpsychism.]