Surely Mr. Mill here demands much more of philosophy than Sir W. Hamilton deems it capable of accomplishing. Why may not Hamilton, like Kant, distinguish between the permanent and necessary, and the variable and contingent—in other words, between the subjective and the objective elements of consciousness, without therefore obtaining a “direct intuition of things in themselves?” Why may he not distinguish between space and time as the forms of our sensitive cognitions, and the things perceived in space and time, which constitute the matter of the same cognitions, without thereby having an intuition, on the one hand, of pure space and time with nothing in them, or on the other, of things in themselves out of space and time? If certain elements are always present in perception, while certain others change with every act, I may surely infer that the one is due to the permanent subject, the other to the variable object, without thereby knowing what each would be if it could be discerned apart from the other. “A direct intuition of things in themselves,” according to Kant and Hamilton, is an intuition of things out of space and time. Does Mr. Mill suppose that any natural Realist professes to have such an intuition?
The same error of supposing that a doctrine of relativity is necessarily a doctrine of Idealism, that “matter known only in relation to us” can mean nothing more than “matter known only through the mental impressions of which it is the unknown cause,”[AC] runs through the whole of Mr. Mill’s argument against this portion of Sir W. Hamilton’s teaching. That argument, though repeated in various forms, may be briefly summed up in one thesis; namely, that the doctrine that our knowledge of matter is wholly relative is incompatible with the distinction, which Hamilton expressly makes, between the primary and secondary qualities of body.
The assumption that these two expressions are or ought to be synonymous is tacitly made by Mr. Mill at the opening of this chapter. He opens it with a passage from the Discussions, in which Hamilton says that the existence of things in themselves is only indirectly revealed to us “through certain qualities related to our faculties of knowledge;” and then proceeds to show that the author did not hold the doctrine which these phrases “seem to convey in the only substantial meaning capable of being attached to them;” namely, “that we know nothing of objects except their existence, and the impressions produced by them upon the human mind.” Having thus quietly assumed that “things in themselves” are identical with “objects,” and “relations” with “impressions on the human mind,” Mr. Mill bases his whole criticism on this tacit petitio principii. He is not aware that though Reid sometimes uses the term relative in this inaccurate sense, Hamilton expressly points out the inaccuracy and explains the proper sense.—(See Reid’s Works, pp. 313, 322.)
The most curious circumstance about this criticism is, that, if not directly borrowed from, it has at least been carefully anticipated by, Hamilton himself. Of the distinction between primary and secondary qualities, as acknowledged by Descartes and Locke, whose theory of external perception is identical with that which Mr. Mill would force on Hamilton himself, Hamilton says: “On the general doctrine, however, of these philosophers, both classes of qualities, as known, are confessedly only states of our own minds; and while we have no right from a subjective affection to infer the existence, far less the corresponding character of the existence, of any objective reality, it is evident that their doctrine, if fairly evolved, would result in a dogmatic or in a sceptical negation of the primary no less than of the secondary qualities of body, as more than appearances in and for us.”[AD] It is astonishing that Mr. Mill, who pounces eagerly on every imaginable instance of Hamilton’s inconsistency, should have neglected to notice this, which, if his criticism be true, is the most glaring inconsistency of all.
Reid’s Works, p. 840.
But Hamilton continues: “It is therefore manifest that the fundamental position of a consistent theory of dualistic realism is—that our cognitions of Extension and its modes are not wholly ideal—that although Space be a native, necessary, à priori form of imagination, and so far, therefore, a mere subjective state, that there is, at the same time, competent to us, in an immediate perception of external things, the consciousness of a really existent, of a really objective, extended world.” Here we have enunciated in one breath, first the subjectivity of space, which is the logical basis of the relative theory of perception; and secondly, the objectivity of the extended world, which is the logical basis of the distinction between primary and secondary qualities. It is manifest, therefore, that Hamilton had not, as Mr. Mill supposes, ceased to hold the one theory when he adopted the other.[AE]
See Examination, p. 28.