229. Hume makes a show of getting rid of this see-saw. Instead of assuming at once the reality of sensation on the strength of its relation to the primary qualities and the reality of these on the strength of their being given in tactual experience, he pronounces sensations alone the real, to which the primary qualities must be reduced, if they are not to disappear altogether. ‘If colours, sounds, tastes, and smells be merely perceptions, nothing we can conceive is possessed of a real, continued, and independent existence’. [1] That they are perceptions is of course undoubted. The question is, whether there is a real something beside and beyond them, contrast with which is implied in speaking of them as ‘_merely_ perceptions.’ The supposed qualities of such a real are ‘motion, extension, and solidity’. [2] To modes of these the other primary qualities enumerated by Locke are reducible; and of these again motion and extension, according to Locke’s account no less than Hume’s own, presuppose solidity. What then do we assert of the real, in contrast with which we talk of perception, as _mere_ perception, when we say that it is solid? ‘In order to form an idea of solidity we must conceive two bodies pressing on each other without any penetration. ... Now, what idea do we form of these bodies? ... To say that we conceive them as solid is to run on _ad infinitum_. To affirm that we paint them out to ourselves as extended, either resolves them all into a false idea or returns in a circle; extension must necessarily be conceived either as coloured, which is a false idea, [3] or as solid, which brings us back to the first question.’ Of solidity, then, the ultimate determination of the supposed real, there is ‘no idea to be formed’ apart from those perceptions to which, as independent of our senses, it is opposed. ‘After exclusion of colours, sounds, heat and cold from the rank of external existences, there remains nothing which can afford us a just and consistent idea of body.’ [1] p. 513 [Book I, part IV., sec. IV.] [2] Ibid. [3] ‘A false idea,’ that is, according to the doctrine that extension is a primary quality, while colour is only an idea of a secondary quality, not resembling the quality as it is in the thing. Locke’s shuffle of ‘body,’ ‘solidity,’ and ‘touch,’ fairly exposed.