255. As it was, he never came fairly to ask himself the fruitful question. How the sciences of quantity ‘continuous and discreet,’ which undoubtedly do exist, are possible to a merely feeling consciousness, because, while professedly reducing all consciousness to this form, he still allowed himself to interpret it in the terms of these sciences and, having done so, could easily account for their apparent ‘abstraction’ from it. If colour is already for feeling a magnitude, as is implied in calling it a ‘composition of coloured points,’ the question, how a knowledge of magnitude is possible, is of course superfluous. It only remains to deal, as Hume professes to do, with the apparent abstraction in mathematics of magnitude from colour and the consequent suppositions of pure space and infinite divisibility. Any ulterior problem he ignores. That magnitude is not any the more a feeling for being ‘endowed with colour’ he shows no suspicion. He pursues his ‘sensationalism’ in short, in its bearing on mathematics, just as far as Berkeley did and no further. The question at issue, as he conceived it, was not as to the possibility of magnitude altogether, but only as to the existence of a vacuum; not as to the possibility of number altogether, but only as to the infinity of its parts. Just as he takes magnitude for granted as found in extension, and extension as equivalent to the feeling of colour, so he takes number for granted, without indeed any explicit account of the impression in which it is to be found, but apparently as found in time, which again is identified with the succession of impressions. In the second part of the Treatise, though the idea of number is assumed and an account is given of it which is supposed to be fatal to the infinite divisibility of extension, we are told nothing of the impression or impressions from which it is derived. In the Fourth Part, however, there is a passage in which a certain consideration of time is spoken of as its source. His account of the relation between Time and Number. 256. In the latter passage, in order to account for the idea of identity, he is supposing ‘a single object placed before us and surveyed for any time without our discovering in it any variation or interruption.’ ‘When we consider any two points of this time,’ he proceeds, ‘we may place them in different lights. We may either survey them at the very same instant; in which case they give us the idea of number, both by themselves and by the object, which must be multiplied in order to be conceived at once, as existent in these two different points of time: or, on the other hand, we may trace the succession of time by a like succession of ideas, and conceiving first one moment, along with the object then existent, imagine afterwards a change in the time without any variation or interruption in the object; in which case it gives us the idea of unity’. [1] [1] P. 490. [Book I, part IV., sec. II.] What does it come to?