The key to all this is not difficult to find. It is simply that objective existence does not mean existence per se; and that a phenomenon does not mean a mere mode of mind. Objective existence is existence as an object, in perception, and therefore in relation; and a phenomenon may be material, as well as mental. The thing per se may be only the unknown cause of what we directly know; but what we directly know is something more than our own sensations. In other words, the phenomenal effect is material as well as the cause, and is, indeed, that from which our primary conceptions of matter are derived. Matter does not cease to be matter when modified by its contact with mind, as iron does not cease to be iron when smelted and forged. A horseshoe is something very different from a piece of iron ore; and a man may be acquainted with the former without ever having seen the latter, or knowing what it is like. But would Mr. Mill therefore say that the horseshoe is merely a subjective affection of the skill of the smith—that it is not iron modified by the workman, but the workman or his art impressed by iron?
If, indeed, Hamilton had said with Locke, that the primary qualities are in the bodies themselves, whether we perceive them or no,[AF] he would have laid himself open to Mr. Mill’s criticism. But he expressly rejects this statement, and contrasts it with the more cautions language of Descartes, “ut sunt, vel saltem esse possunt.”[AG] The secondary qualities are mere affections of consciousness, which, cannot be conceived as existing except in a conscious subject. The primary qualities are qualities of body, as perceived in relation to the percipient mind, i.e., of the phenomenal body perceived as in space. How far they exist in the real body out of relation to us, Hamilton does not attempt to decide.[AH] They are inseparable from our conception of body, which, is derived exclusively from the phenomenon; they may or may not be separable from the thing as it is in itself.
Essay, ii 8, § 23.
Reid’s Works, p. 839.
We have been content to argue this question, as Mr. Mill himself argues it, on the supposition that Sir W. Hamilton held that we are directly percipient of primary qualities in external bodies. Strictly speaking, however, Hamilton held that the primary qualities are immediately perceived only in our organism as extended, and inferred to exist in extra-organic bodies. The external world is immediately apprehended only in its secundo-primary character, as resisting our locomotive energy. But as the organism, in this theory, is a material non-ego equally with the rest of matter, and as to press this distinction would only affect the verbal accuracy, not the substantial justice, of Mr. Mill’s criticisms, we have preferred to meet him on the ground he has himself chosen. The same error, of supposing that “presentationism” is identical with “noumenalism,” and “phenomenalism” with “representationism,” runs through the whole of Mr. Stirling’s recent criticism of Hamilton’s theory of perception. It is curious, however, that the very passage (Lectures, i., p. 146) which Mr. Mill cites as proving that Hamilton, in spite of his professed phenomenalism, was an unconscious noumenalist, is employed by Mr. Stirling to prove that, in spite of his professed presentationism, he was an unconscious representationist. The two critics tilt at Hamilton from opposite quarters: he has only to stand aside and let them run against each other.
Under this explanation, it is manifest that the doctrine, that matter as a subject or substratum of attributes is unknown and unknowable, is totally different from that of cosmothetic idealism, with which Mr Mill confounds it;[AI] and that a philosopher may without inconsistency accept the former and reject the latter. The former, while it holds the material substance to be unknown, does not deny that some of the attributes of matter are perceived immediately as material, though, it may be, modified by contact with mind. The latter maintains that the attributes, as well as the substance, are not perceived immediately as material, but mediately through the intervention of immaterial representatives. It is also manifest that, in answer to Mr. Mill’s question, which of Hamilton’s two “cardinal doctrines,” Relativity or Natural Realism, “is to be taken in a non-natural sense,”[AJ] we must say, neither. The two doctrines are quite compatible with each other, and neither requires a non-natural interpretation to reconcile it to its companion.