Visible extension, then, or the perception of colours external to colours, being admitted, Mr Bailey's argument, if he still adheres to it, must be presented to us in this form. He must maintain that the theory requires that the objects of touch should not only be suggested by the visual objects with which they have been associated, but that they should actually be seen. And then he must maintain that no power of association can enable us to see an object which can only be touched—a position which, certainly, no one will controvert. The simple answer to all which, is, that we never do see tangible objects—that the theory never requires we should, and that no power of association is necessary to account for a phenomenon which never takes place.
We cannot help thinking, that not a little of the misconception on this subject which prevails in the writings of Mr Bailey, and, we may add, of many other philosophers, originates in the supposition that we identify vision with the eye in the mere act of seeing, and in their taking it for granted that sight of itself informs us that we possess such an organ as the eye. Of course, if we suppose that we know instinctively, or intuitively, from the mere act of seeing, that the eye is the organ of vision, that it forms a part of the body we behold, and is located in the head, it requires no conjurer to prove that we must have an instinctive, or intuitive, knowledge of visible things as larger than that organ, and, consequently, as external to it. In this case, no process of association is necessary to account for our knowledge of the distance of objects. That knowledge must be directly given in the very function and exercise of vision, as every one will admit, without going to the expense of an octavo volume to have it proved.
But we hold that no truth in mental philosophy is more incontestable than this, that the sight originally, and of itself, furnishes us with no knowledge of the eye, as we now know that organ to exist. It does not inform us that we have an eye at all. And here we may hazard an observation, which, simple as it is, appears to us to be new, and not unimportant in aiding us to unravel the mysteries of sensation; which observation is, that, in no case whatever, does any sense inform us of the existence of its appropriate organ, or of the relation which subsists between that organ and its objects, but that the interposition of some other sense[36] is invariably required to give us this information. This truth, which we believe holds good with regard to all the senses, is most strikingly exemplified in the case of vision, as we shall now endeavour to illustrate.
Let us begin by supposing that man is a mere "power of seeing". Under this supposition, we must hold that the periphery of vision is one and the same with the periphery of visible space; and the two peripheries being identical, of course whatever objects lie within the sphere of the one must lie within the sphere of the other also. Perhaps, strictly speaking, it is wrong to say that these objects are apprehended as internal to the sight; for the conception of internality implies the conception of externality, and neither of these conceptions can, as yet, be realized. But it is obvious what the expression internal means; and it is unobjectionable, when understood to signify that the Seeing Power, the Seeing Act, and the Seen Things, co-exist in a synthesis in which there is no interval or discrimination. For, suppose that we know instinctively that the seen things occupy a locality separate from the sight. But that implies that we instinctively know that the sight occupies a locality separate from them. But such a supposition is a falling back upon the notion just reprobated, that the mere act of seeing can indicate its own organ, or can localise the visual phenomena in the eye—a position which, we presume, no philosopher will be hardy enough to maintain, when called upon to do so, broadly and unequivocally. The conclusion, therefore, is irresistible, that, in mere vision, the sight and its objects cling together in a union or synthesis, which no function of that sense, and no knowledge imparted to us by it, (and, according to the supposition, we have, as yet, no other knowledge,) can enable us to discriminate or dissolve. Where the seeing is, there is the thing seen, and where the thing seen is, there is the seeing of it.
But man is not a mere seeing animal. He has other senses besides: He has, for example, the sense of touch, and one of the most important offices which this sense performs, is to break up the identity or cohesion which subsists between sight and its objects. And how? We answer, by teaching us to associate vision in general, or the abstract condition regulating our visual impressions, with the presence of the small tangible body we call the eye, and vision in particular, or the individual sensations of vision, (i.e. colours,) with the presence of immeasurably larger bodies revealed to us by touch, and tangibly external to the tangible eye. Sight, as we have said, does not inform us that its sensations are situated in the eye: it does not inform us that we have an eye at all. Neither does touch inform us that our visual sensations are located in the eye. It does not lead us to associate with the eye any of the visual phenomena or operations in the first instance. If it did, it would (firstly) either be impossible for it afterwards to induce us to associate them with the presence of tangible bodies distant and different from the eye: or, (secondly), such an association would merely give birth to the abstract knowledge or conclusion, that these bodies were in one place, while the sensations suggesting them were felt to be associated with something in another place; colour would not be seen—as it is—incarnated with body: or, (thirdly), we should be compelled to postulate for the eye, as many philosophers have done, in our opinion, most unwarrantably, "a faculty of projection"[37] by which it might dissolve the association between itself and its sensations, throwing off the latter in the form of colours over the surface of things, and reversing the old Epicurean doctrine that perception is kept up by the transit to the sensorium of the ghosts or simulacra of things,
Quæ, quasi membranæ, summo de corpore rerum,
Direptæ, volitant ultro citroque per auras.[38]
It is difficult to say whether the hypothesis of "cast-off films" is more absurd when we make the films come from things to us as spectral effluxes, or go from us to them in the semblance of colours.
But according to the present view no such incomprehensible faculty, no such crude and untenable hypothesis, is required. Before the touch has informed us that we have an eye, before it has led us to associate any thing visual with the eye, it has already taught us to associate in place the sensations of vision (colours) with the presence of tangible objects which are not the eye. Therefore, when the touch discovers the eye, and induces us to associate vision in some way with it, it cannot be the particular sensations of vision called colours which it leads us to associate with that organ; for these have been already associated with something very different. If it be not colours, then what is it that the touch compels us to associate with the eye? We answer that it is the abstract condition of impressions as the general law on which all seeing depends, but as quite distinct from the particular visual sensations apprehended in virtue of the observance of that law.
Nor is it at all difficult to understand how this general condition comes to be associated with the eye, and how the particular visual sensations come to be associated with something distant from the eye: and further, how this association of the condition with one thing, and of the sensations with another thing, (an association established by the touch and not by the sight,) dissolves the primary synthesis of seeing and colours. It is to be observed that there are two stages in the process by which this secernment is brought about—First, the stage in which the visual phenomena are associated with things different from the organ of vision, the very existence of which is as yet unknown. Let us suppose, then, the function of sight to be in operation. We behold a visible object—a particular colour. Let the touch now come into play. We feel a tangible object—say a book. Now from the mere fact of the visible and the tangible object being seen and felt together, we could not associate them in place; for it is quite possible that the tangible object may admit of being withdrawn, and yet the visible object remain: and if so, no association of the two in place can be established. But this is a point that can only be determined by experience; and what says that wise instructor? We withdraw the tangible object. The visible object, too, disappears: it leaves its place. We replace the tangible object—the visible object reappears in statu quo. There is no occasion to vary the experiment. If we find that the visible object invariably leaves its place when the tangible object leaves its, and that the one invariably comes back when the other returns, we have brought forward quite enough to establish an inevitable association in place between the two. The two places are henceforth regarded, not as two, but as one and the same.