perhaps rather have said that it is so distinguished and referred ‘by the mind.’ He considers the simple idea not, as it truly is, the mind itself in a certain relation, but a datum or material of the mind, upon which it performs certain operations as upon something other than itself, though all the while it is constituted, at least in its actuality, by this material. Between the reference of the simple idea to the thing, however, by itself and ‘by the mind,’ there is no essential difference. In either case the reference is inconsistent with the simplicity of the simple idea; and if the latter expression avoids the seeming awkwardness of ascribing activity to the idea, it yet ascribes it to the mind in that elementary stage in which, according to Locke, it is merely receptive. And is equivalent to what he afterwards calls ‘knowledge of identity’. Only as such can it be named. 25. So much for the theory ‘of ideas.’ As if, however, in treating of ideas he had been treating of anything else than knowledge, he afterwards considers ‘knowledge’ in a book by itself (the fourth) under that title, and here the question as to the relation between idea and thing comes before him in a somewhat different shape. According to his well-known definition, knowledge is the perception of the agreement or disagreement of any of our ideas. The agreement or disagreement may be of four sorts. It may be in the way (1) of identity, (2) of relation, (3) of co-existence, (4) of real existence. In his account of the last sort of agreement, it may be remarked by the way, he departs at once and openly from his definition, making it an agreement, not of idea with idea, but of an idea with ‘actual real existence.’ The fatal but connatural wound in his system, which this inconsistency marks, will appear more fully below. For the present, our concern is for the adjustment of the definition of knowledge to the doctrine of the simple idea as the beginning of knowledge. According to the definition, it cannot be the simple idea, as such, that constitutes this beginning, but only the perception of agreement or disagreement between simple ideas. ‘There could be no room,’ says Locke distinctly, ‘for any positive knowledge at all, if we could not distinguish any relation between our ideas.’ (Book IV. chap. i. sec. 5.) Yet in the very context where he makes this statement, the perception of relation is put as a distinct kind of knowledge apart from others. In his account of the other kinds, however, he is faithful to his definition, and treats each as a perception (_i.e._ a judgment) of a relation in the way of agreement or disagreement. The primary knowledge is that of identity--the knowledge of an idea as identical with itself. ‘A man infallibly knows, as soon as ever he has them in his mind, that the ideas he calls _white_ and _round_, are the very ideas they are, and not other ideas which he calls _red_ and _square_.’ (Book IV. chap. i. sec.