its special character as spatial and temporal it presupposed a percipient, and the other endeavouring to show that the primary qualities are as relative to perception as the secondary. Unfortunately for their view, in order to think of bodies in space as dependent on the mind, it is necessary to think of them as being in the end only certain sensations or certain combinations of sensations which may be called appearances. For only sensations or combinations of them can be thought of as at once dependent on the mind, and capable with any plausibility of being identified with bodies in space. In other words, in order to think of the world as dependent on the mind, we have to think of it as consisting only of a succession of appearances, and in fact Berkeley, and, at certain times, Kant, did think of it in this way. [2] Cf. p. 119. [3] Though not apart from relation to the mind of some other kind. That this is the inevitable result of idealism is not noticed, so long as it is supposed that the essential relation of realities to the mind consists in their being known; for, as we have seen, nothing is thereby implied as to their special nature. To say of a reality that it is essentially an object of knowledge is merely to add to the particular nature ordinarily attributed to the existent in question the further characteristic that it must be known.[4] Moreover, since in fact, though contrary to the theory, any reality exists independently of the knowledge of it, when the relation thought of between a reality and the mind is _solely_ that of knowledge, the realities can be thought of as independent of the mind. Consequently, the physical world can be thought to have that independence of the mind which the ordinary man attributes to it, and, therefore, need not be conceived as only a succession of appearances. But the advantage of this form of idealism is really derived from the very fact which it is the aim of idealism in general to deny. For the conclusion that the physical world consists of a succession of appearances is only avoided by taking into account the relation of realities to the mind by way of knowledge, and, then, without being aware of the inconsistency, making use of the independent existence of the reality known. [4] Cf. p. 116.