66. In short, as we have seen the simple idea of sensation emerge from Locke’s inquiry as to the beginning of knowledge transformed into the judgment, ‘I have an idea different from other ideas which I did not make for myself,’ so now from the inquiry as to the correspondence between knowledge and reality it emerges as the consciousness of a thing now acting upon me, which has continued to exist since it acted on me before, and in which, as in a common cause, have existed together powers to affect me which have never affected me together. If in the one form the operation of thought in sense, the ‘creation of the understanding’ within the simple idea, is only latent or potential, in the other it is actual and explicit. The relations of substance and quality, of cause and effect, and of identity--all ‘inventions of the mind’--are necessarily involved in the immediate, spontaneous testimony of passive sense. Locke’s treatment of relations of cause and identity. 67. It will be noticed that it is upon the first of these, the relation of substance and quality, that our examination of Locke’s Essay has so far chiefly gathered. In this it follows the course taken by Locke himself. Of the idea of substance, _eo nomine_, he treats at large: of cause and identity (apart from the special question of personal identity) he says little. So, too, the ‘report of the senses’ is commonly exhibited as announcing the sensible qualities of a thing rather than the agency of a cause or continuity of existence. The difference, of course, is mainly verbal. Sensible qualities being, as Locke constantly insists, nothing but ‘powers to operate on our senses’ directly or indirectly, the substance or thing, as the source of these, takes the character of a cause. Again, as the sensible quality is supposed to be one and the same in manifold separate cases of being felt, it has identity in contrast with the variety of these cases, even as the thing has, on its part, in contrast with the variety of its qualities. Something, however, remains to be said of Locke’s treatment of the ideas of cause and identity in the short passages where he treats of them expressly. Here, too, we shall find the same contrast between the given and the invented, tacitly contradicted by an account of the given in terms of the invented. That from which he derives idea of cause pre-supposes it.