27. Upon analysis, then, of Locke’s account of the most elementary knowledge, the perception of identity or agreement of an idea with itself, we find that like the ‘simple idea,’ which he elsewhere makes the beginning of knowledge, it really means the reference of a sensation to a conception of a permanent object or subject, [1] either in such a judgment as ‘this is white’ (_sc._ a white thing), or in the more elementary one, ‘this is an object to me.’ In the latter form the judgment represents what Locke puts as the consciousness, ‘I have an idea,’ or as the ‘consideration that the idea is actually there;’ in the former it represents what he calls ‘the knowledge that the idea which I have in my mind and which I call white is the very idea it is, and not the idea which I call red.’ It is only because _referred_, as above, that the sensation is in Locke’s phraseology ‘a testimony’ or ‘report’ of something. As we said above, his notion of the beginning of knowledge is expressed not merely in the formula ‘I have an idea different from other ideas,’ but with the addition, ‘which I did not make for myself.’ [2] The simple idea is supposed to testify to something without that caused it, and it is this interpretation of it which makes it with him the ultimate criterion of reality. But unless it were at once distinguished from and referred to both a thing of which it is an effect and a subject of which it is an experience, it could not in the first place testify to anything, nor secondly to a thing as made for, not by, the subject. This brings us, however, upon Locke’s whole theory of ‘real existence,’ which requires fuller consideration. [1] For a recognition by Locke of the correlativity of these (of which more will have to be said below) cf. Book II. chap. xxiii. sec. 15. ‘Whilst I know by seeing or hearing, &c., that there is some corporeal being without me, the object of that sensation, I do more certainly know that there is some spiritual being within me that sees and hears.’ [2] Cf. Book II. chap. xii. sec. 1. What did he mean by this? 28. It is a theory, we must premise, which is nowhere explicitly stated. It has to be gathered chiefly from those passages of the second book in which he treats of ‘complex’ or ‘artificial’ ideas in distinction from simple ones, which are necessarily real, and from the discussion in the fourth book of the ‘extent’ and ‘reality’ of knowledge. We have, however, to begin with, in the enumeration of simple ideas, a mention of ‘existence,’ as one of those ‘received alike through all the ways of sensation and reflection.’ It is an idea ‘suggested to the understanding by every object without and every idea within. When ideas are in our minds, we consider them as being actually there, as well as we consider things to be actually without us; which is, that they exist, or have existence.’ (Book II. chap. vii. sec. 7.)