53. In calling a sensation or idea the product of a power, substance is presupposed just as much as in calling it a sensible quality; only that with Locke ‘quality’ conveyed the notion of inherence in the substance, power that of relation to an effect not _in_ the substance itself. ‘Secondary qualities are nothing but the powers which _substances_ have to produce several ideas in us by our senses, which ideas are not in the things themselves, otherwise than as anything is in its cause.’ (Book II. chap, xxiii. sec. 9.) ‘Most of the simple ideas, that make up our complex ideas of substances, are only powers ... or relations to other substances (or, as he explains elsewhere, ‘relations to our perceptions,’ [1]), and are not really in the substance considered barely in itself.’ (Book II. chap, xxiii. sec. 37, and xxxi. 8.) That this implies the inclusion of the idea of cause in that of substance, appears from Locke’s statement that ‘whatever is considered by us to operate to the producing any particular simple idea which did not before exist, hath thereby in our minds the relation of a cause.’ (Book II. chap. xxvi. sec. 1.) Thus to be conscious of the reality of a simple idea, as that which is not made by the subject of the idea, but results from a power in a thing, is to have the idea of substance as cause. This latter idea must be the condition of the consciousness of reality. If the consciousness of reality is implied in the beginning of knowledge, so must the correlative ideas be of cause and substance. [1] Book II. chap. xxi. sec. 3. How do we know that ideas correspond to reality of things? Locke’s answer.