143. We have finally to notice the way in which Locke maintains our knowledge of the ‘real existence’ of thinking substance, both as that which ‘we call our mind,’ and as God. Of the former first. ‘Experience convinces us that we have an intuitive knowledge of our own existence.... If I know I feel pain, it is evident I have as certain perception of my own existence as of the pain I feel. If I know I doubt, I have as certain perception of the existence of the thing doubting as of that thought which I call doubt’ (Book IV. chap. ix. sec. 3). Upon this the remark must occur that the existence of a painful feeling is one thing; the existence of a permanent subject, remaining the same with itself, when the feeling is over, and through the succession of other feelings, quite another. The latter is what is meant by my own existence, of which undoubtedly there is a ‘certain perception,’ if the feeling of pain has become the ‘knowledge that I feel pain,’ and if by the ‘I’ is understood such a permanent subject. That the feeling, as ‘simple idea,’ is taken to begin with by Locke for the knowledge that I feel something, we have sufficiently seen. [1] Just as, in virtue of this conversion, it gives us ‘assurance’ of the real existence of the outer thing or material substance on the one side, so of the thinking substance on the other. It carries with it the certainty at once that I have a feeling, and that something makes me feel. But whereas, after the conversion of feeling into a felt thing has been throughout assumed--as indeed otherwise feeling could not be spoken of--a further question is raised, which causes much embarrassment, as to the real existence of such thing; on the contrary, the reference of the feeling to the _thinking_ thing is taken as carrying with it the real existence of such thing. The question whether it really exists or no is only once raised, and then summarily settled by the sentence we have quoted, while the reality whether of existence or of essence on the part of the outward thing, as we have found to our cost, is the main burden of the Third and Fourth Books. [1] See above, paragraphs 26 and following, and 59 and following. It cannot be known consistently with Locke’s doctrine of real existence.