230. Our examination of Locke has shown us how it is that his interpretation of ideas by reference to body is fairly open to this attack. It is so because, in thus interpreting them, he did not know what he was really about. He thought he was explaining ideas of sense according to the only method of explanation which he recognises--the method of resolving complex into simple ideas, and of ‘sending a man to his senses’ for a knowledge of the simple. In fact, however, when he explained ideas of sense as derived from the qualities of body, he was explaining simple ideas by reference to that which, according to his own showing, is a complex idea. To say that, as Locke understood the derivation in question, the primary qualities are an ἄιτιον γενέσεως to the ideas of secondary qualities, but not an ἄιτιον γνώσεως [1]--that without our having ideas of them they cause those ideas of sense from which afterwards our ideas of the primary qualities are formed--is to suppose an order of reality other than the order of our sensitive experience, and thus to contradict Locke’s fundamental doctrine that the genesis of ideas is to be found by observing their succession in ‘our own breasts.’ It is not thus that Locke himself escapes the difficulty. As we have seen, he supposes our ideas of sense to be from the beginning ideas of the qualities of bodies, and virtually justifies the supposition by sending the reader to his sense of touch for that idea of solidity in which, as he defines it, all the primary qualities are involved. That the sense in question does not really yield the idea is what Hume points out when he says that, ‘though bodies are felt by means of their solidity, yet the feeling is quite a different thing from the solidity, nor have they the least resemblance to each other.’ In other words, having come to suppose that there are solid bodies, we explain our feeling as due to their solidity; but we may not at once interpret feeling as the result of solidity, and treat solidity as itself a feeling. It was by allowing himself so to treat it that Locke disguised from himself the objection to his interpretation of feeling. Hume tears off the disguise, and in effect gives him the choice of being convicted either of reasoning in a circle or of explaining the simple idea by reference to the complex. The solidity, which is to explain feeling, can itself only be explained by reference to body. If body is only a complex of ideas of sense, in referring tactual feeling to it we are explaining a simple idea by reference to a compound one. If it is not, how is it to be defined except in the ‘circular’ way, which Locke in fact adopts when he makes body a ‘texture of solid parts’ and solidity a relation of bodies? [2] [1] [Greek ἄιτιον γενέσεως (aition geneseos) = cause of coming-to-be, ἄιτιον γνώσεως (aition gnoseos) = cause of being known. Tr.] [2] See above, paragraph 101. True rationale of Locke’s doctrine.