The fact that colours mix, not to the purpose.
248. This plausibility depends chiefly on our reading into Hume’s doctrine a physical theory which, as implying a distinction between feeling and its real but unfelt cause, is strictly incompatible with it. Is it not an undoubted fact, the reader asks, that two colours may combine to produce a third different from both—that red and yellow, for instance, together produce orange? Is not this already an instance of a compound impression? Why may not a like composition of unextended impressions of colour constitute an impression different from any one of the component impressions, viz. extended colour? A moment’s consideration, however, will show that no one has a conscious sensation at once of red and yellow, and of orange as a compound of the two. The elements which combine to produce the colour called orange are not—as they ought to be if it is to be a case of compound impression in Hume’s sense—feelings of the person who sees the orange colour, but certain known causes of feeling, confused in language with the feelings, which separately they might produce, but which in fact they do not produce when they combine to give the sensation of orange; and to such causes of feeling, which are not themselves feelings, Hume properly can have nothing to say.
How Hume avoids appearance of identifying space with colour, and accounts for the abstraction of space.
249. So far we have been considering the composition of impressions generally, without special reference to extension. The contradiction pointed out arises from the confusion between impressions as felt and impressions as thought of; colour, between feelings as they are in themselves, presented successively in time, and feelings as determined by relation to the thinking subject, which takes them out of the flux of time and converts them into members of a permanent whole. It is in this form that the confusion is most apt to elude us. When the conceived object is one of which the qualities can really be felt, e.g. colour, we readily forget that a felt quality is no longer simply a feeling. But the case is different when the object is one, like extension, which forces on us the question whether its qualities can be felt, or presented in feeling, at all. A compound of impressions of colour, to adopt Hume’s phraseology, even if such composition were possible, would still be nothing else than an impression of colour. In more accurate language, the conception, which results from the action of thought upon feelings of colour, can only be a conception of colour. Is extension, then, the same as colour? To say that it was would imply that geometry was a science of colour; and Hume, though ready enough to outrage ‘Metaphysics and School Divinity,’ always stops reverently short of direct offence to the mathematical sciences. As has been said above, of the three main questions about the idea of extension which his doctrine raises—Is it itself extended? Is it possible without reference to something other than a possible impression? Is it the same as the idea of colour or tangibility?—the last is the only one which he can scarcely even profess to answer in the affirmative. [1] Even when he has gone so far as to speak of the parts of a perception, a sound instinct compels him, instead of identifying the perception directly with extension, to speak of it as ‘affording through the situation of its parts the notion of’ extension. [2] In like manner, when he has asserted extension to be a compound of impressions, he avoids the proper consequence of the assertion by speaking of the component impressions as those, not of colour but, of coloured points, ‘atoms or corpuscles endowed with colour and solidity;’ and, again, does not call extension the compound of these simply, but the compound of them as ‘disposed in a certain manner.’ When the idea which is a copy of this impression has to be spoken of, the expression is varied again. It is an ‘idea of the coloured points and of the manner of their appearance,’ or of their ‘disposition.’ The disposition of the parts having been thus virtually distinguished from their colour, it is easy to suppose that, finding a likeness in the disposition of points under every unlikeness of their colour, ‘we omit the peculiarities of colour, as far as possible, and found an abstract idea merely on that disposition of points, or manner of appearance, in which they agree. Nay, even when the resemblance is carried beyond the objects of one sense, and the impressions of touch are found to be similar to those of sight in the disposition of their parts, this does not hinder the abstract idea from representing both on account of their resemblance’. [3]
[1] Above, paragraph 233. Though, as we shall see, he does so in one passage.
[2] Above, paragraph 235.
[3] P. 341 [Book I, part II., sec. III.]
In so doing, he implies that space is a relation, and a relation which is not a possible impression.
250. If words have any meaning, the above must imply that the disposition of points is at least a different idea from either colour or tangibility, however impossible it may be for us to experience it without one or other of the latter. Nor can we suppose that this impression, other than colour, is one that first results from the composition of colours, even if we admit that such composition could yield a result different from colour. According to Hume, the components of the compound impression are already impressions of coloured ‘points, atoms, or corpuscles,’ and such points imply just that limitation by mutual externality, which is already the disposition in question. Is this ‘disposition,’ then, an impression of sensation? If so, ‘through which of the senses is it received? If it be perceived by the eyes it must be a colour,’ &c. &c.; [1] but from colour, the impression with which Hume would have identified it if he could, he yet finds himself obliged virtually to distinguish it. It is a relation, and not even one of those relations, such as resemblance, which in Hume’s language, ‘depending on the nature of the impressions related,’ [2] may plausibly be reckoned to be themselves impressions. The ‘disposition’ of parts and their ‘situation’ he uses interchangeably, and the situation of impressions he expressly opposes to their ‘nature’ [3]—that nature in respect of which all impressions, call them what we like, are ‘originally on the same footing’ with pain and pleasure. Consistently with this he pronounces the ‘external position’ of objects—their position as bodies external to each other and to our body—to be no datum of sense, no impression or idea, at all. [4] Our belief in it has to be accounted for as a complex result of ‘propensities to feign.’ How, then, can there be an impression of that which does not belong to the nature of any impression? What difference is there between ‘bodies’ and ‘corpuscles endowed with colour and solidity,’ that the outwardness of the latter to each other—also called their ‘distance’ from each, other [5]—should be an impression, while it is admitted that the same relation between ‘bodies’ cannot be so?
[1] Above, paragraph 208.