These are usually called powers.’ (Book II. chap. viii. sec. 15, 23.) ‘Simple idea’ represented as involving a theory of its own cause. 20. What we have here is a theory of the causes of simple ideas; but we shall find Locke constantly representing this theory as a simple idea itself, or the simple idea as involving this theory. By this unconscious device he is enabled readily to exhibit the genesis of knowledge out of ‘simple ideas,’ but it is at the cost of converting these into ‘creations of the mind,’ which with him are the antitheses of ‘facts’ or ‘reality.’ The process of conversion takes a different form as applied respectively to the ideas of primary and to those of secondary qualities. We propose to follow it in the latter application first. Phrases in which this is implied. 21. The simple idea caused by a quality he calls the idea _of_ that quality. Under cover of this phrase, he not only identifies the idea of a primary quality with the quality itself of which he supposes it to be a copy, but he also habitually regards the idea of a secondary quality as the consciousness of a quality _of a thing_, though under warning that the quality as it is to consciousness is not as it is in the thing. This reservation rather adds to the confusion. There are in fact, according to Locke, as appears from his distinction between the ‘nominal’ and ‘real essence,’ two different things denoted by every common noun; the thing as it is in itself or in nature, and the thing as it is for consciousness. The former is the thing as constituted by a certain configuration of particles, which is only an object for the physical philosopher, and never fully cognisable even by him; [1] the latter is the thing as we see and hear and smell it. Now to a thing in this latter sense, according to Locke, such a simple idea as to the philosopher is one of a secondary quality (_i.e._ not a copy, but an effect, of something in a body), is already in the origin of knowledge referred as a quality, though without distinction of primary and secondary. He does not indeed state this in so many words. To have done so might have forced him to reconsider his doctrine of the mere passivity of the mind in respect of simple ideas. But it is implied in his constant use of such phrases as ‘reports of the senses,’ ‘inlet through the senses’--which have no meaning unless something is reported, something let in--and in the familiar comparison of the understanding to a ‘closet, wholly shut from light, with only some little opening left, to let in external visible resemblances, or ideas, of things without.’ (Book II. chap. xi. sec. 17.) [1] This distinction is more fully treated below, paragraphs 88, &c. Feeling and felt thing confused.