269. When, as with Hume, it is only in its application to space and time that the question of infinite divisibility is treated, its true nature is more easily disguised, for the reason already indicated, that space and time are not necessarily considered as quanta. When Hume, indeed, speaks of space as a ‘composition of parts’ or ‘made up of points,’ he is of course treating it as a quantum; but we shall find that in seeking to avoid the necessary consequence of its being a quantum--the consequence, namely, that it is infinitely divisible--he can take advantage of the possibility of treating it as the simple, unquantified, relation of externality. We have already spoken of the dexterity with which, having shown that all divisibility, because into impressions, is into simple parts, he turns this into an argument in favour of the composition of space by impressions. ‘Our idea of space is compounded of parts which are indivisible.’ Let us take one of these parts, then, and ask what sort of idea it is: ‘let us form a judgment of its nature and qualities.’ ‘’Tis plain it is not an idea of extension: for the idea of extension consists of parts; and this idea, according to the supposition, is perfectly simple and indivisible. Is it therefore nothing? That is impossible,’ for it would imply that a real idea was composed of nonentities. The way out of the difficulty is to ‘endow the simple parts with colour and solidity.’ In words already quoted, ‘that compound impression, which represents extension, consists of several lesser impressions, that are indivisible to the eye or feeling, and may be called impressions of atoms or corpuscles endowed with colour and solidity.’ (Part II. § 3, near the end.) Colours or coloured points? What is the difference?