Blackwood's Magazine/Volume 54/Issue 337/A Speculation on the Senses
A SPECULATION ON THE SENSES.
How can that which is a purely subjective affection—in other words, which is dependent upon us as a mere modification of our sentient nature—acquire, nevertheless, such a distinct objective reality, as shall compel us to acknowledge it as an independent creation, the permanent existence of which, is beyond the control of all that we can either do or think? Such is the form to which all the questions of speculation may be ultimately reduced. And all the solutions which have hitherto been propounded as answers to the problem, may be generalized into these two: either consciousness is able to transcend, or go beyond itself; or else the whole pomp, and pageantry, and magnificence, which we miscall the external universe, are nothing but our mental phantasmagoria, nothing but states of our poor, finite, subjective selves.
But it has been asked again and again, in reference to these two solulutions, can a man overstep the limits of himself—of his own consciousness? If he can, then says the querist, the reality of the external world is indeed guaranteed; but what an insoluble, inextricable contradiction is here: that a man should overstep the limits of the very nature which is his, just because he cannot overstep it! And if he cannot, then says the same querist, then is the external universe an empty name—a mere unmeaning sound; and our most inveterate convictions are all dissipated like dreams.
Astute reasoner! the dilemma is very just, and is very formidable; and upon the one or other of its horns, has been transfixed every adventurer that has hitherto gone forth on the knight-errantry of speculation. Every man who lays claim to a direct knowledge of something different from himself, perishes impaled on the contradiction involved in the assumption, that consciousness can transcend itself: and every man who disclaims such knowledge, expires in the vacuum of idealism, where nothing grows but the dependent and transitory productions of a delusive and constantly shifting consciousness.
But is there no other way in which the question can be resolved? We think that there is. In the following demonstration, we think that we can vindicate the objective reality of things—(a vindication which, we would remark by the way. is of no value whatever, in so far as that objective reality is concerned, but only as being instrumental to the ascertainment of the laws which regulate the whole process of sensation;)—we think that we can accomplish this, without, on the one hand, forcing consciousness to overstep itself, and on the other hand, without reducing that reality to the delusive impressions of an understanding born but to deceive. Whatever the defects of our proposed demonstration may be, we flatter ourselves that the dilemma just noticed as so fatal to every other solution, will be utterly powerless when brought to bear against it: and we conceive, that the point of a third alternative must be sharpened by the controversialist who would bring us to the dust. It is a new argument, and will require a new answer. We moreover pledge ourselves, that abstruse as the subject is, both the question, and our attempted solution of it, shall be presented to the reader in such a shape as shall compel him to understand them.
Our pioneer shall be a very plain and palpable illustration. Let A be a circle, containing within it X Y Z.
X Y and Z lie within the circle; and the question is, by what art or artifice—we might almost say by what sorcery—can they be transplanted out of it, without at the same time being made to overpass the limits of the sphere? There are just four conceivable answers to this question—answers illustrative of three great schools of philosophy, and of a fourth which is now fighting for existence.
1. One man will meet the difficulty boldly, and say — "X Y and Z certainly lie within the circle, but I believe they lie without it. How this should be, I know not. I merely state what I conceive to be the fact. The modus operandi is beyond my comprehension." This man's answer is contradictory, and will never do.
2. Another man will deny the possibility of the transference — "X Y and Z," he will say, "are generated within the circle in obedience to its own laws. They form part and parcel of the sphere; and every endeavour to regard them as endowed with an extrinsic existence, must end in the discomfiture of him who makes the attempt." This man declines giving any answer to the problem. We ask him how X Y and Z can be projected beyond the circle without transgressing its limits; and he answers that they never are, and never can be so projected.
3. A third man will postulate as the cause of X Y Z a transcendent X Y Z — that is, a cause lying external to the sphere; and by referring the former to the latter, he will obtain for X Y Z, not certainly a real externality, which is the thing wanted, but a quasi-externality, with which, as the best that is to be had, he will in all probability rest contented. "X Y and Z," he will say, "are projected, as it were, out of the circle." This answer leaves the question as much unsolved as ever. Or,
4. A fourth man (and we beg the reader's attention to this man's answer, tor it forms the fulcrum or cardinal point on which our whole demonstration turns)—a fourth man will say, "If the circle could only be brought within itself; so—
then the difficulty would disappear—the problem would be completely solved. X Y Z must now of necessity fall as extrinsic to the circle A; and this, too, (which is the material part of the solution,) without the limits of the circle A being overstepped."
Perhaps this may appear very like quibbling; perhaps it may be regarded as a very absurd solution—a very shallow evasion of the difficulty. Nevertheless, shallow or quibbling as it may seem, we venture to predict, that when the breath of life shall have been breathed into the bones of the above dead illustration, this last answer will be found to afford a most exact picture and explanation of the matter we have to deal with. Let our illustration, then, stand forth as a living process. The large circle A we shall call our whole sphere of sense, in so far as it deals with objective existence—and X Y Z shall be certain sensations of colour, figure, weight, hardness, and so forth, comprehended within it. The question then is—how can these sensations, without being ejected from the sphere of sense within which they lie, assume the status and the character of real independent existences? How can they be objects, and yet remain sensations?
Nothing will be lost on the score of distinctness, if we retrace, in the living sense, the footprints we have already trod in explicating the inanimate illustration. Neither will any harm be done, should we employ very much the same phraseology. We answer, then, that here, too, there are just four conceivable ways in which this question can be met.
I. The man of common sense, (so called,) who aspires to be somewhat of a philosopher, will face the question boldly, and will say, "I feel that colour and hardness, for instance, lie entirely within the sphere of sense, and are mere modifications of my subjective nature. At the same time, I feel that colour and hardness constitute a real object, which exists out of the sphere of sense, independently of me and all my modifications. How this should be, I know not; I merely state the fact as I imagine myself to find it. The modus is beyond my comprehension." This man belongs to the school of Natural Realists. If he merely affirmed or postulated a miracle in what he uttered, we should have little to say against him, (for the whole process of sensation is indeed miraculous.) But he postulates more than a miracle; he postulates a contradiction, in the very contemplation of which our reason is unhinged.
2. Another man will deny that our sensations ever transcend the sphere of sense, or attain a real objective existence. "Colour, hardness, figure, and so forth," he will say, "are generated within the sphere of sense, in obedience to its own original laws. They form integral parts of the sphere; and he who endeavours to construe them to his own mind as embodied in extrinsic independent existences, must for ever be foiled in the attempt." This man declines giving any answer to the problem. We ask, how can our sensations be embodied in distinct permanent realities? And he replies, that they never are and never can be so embodied. This man is an Idealist—or as we would term him, (to distinguish him from another species about to be mentioned, of the same genus,) an Acosmical Idealist; that is, an Idealist who absolutely denies the existence of an independent material world.
3. A third man will postulate as the cause of our sensations of hardness, colour, &c., a transcendent something, of which he knows nothing, except that he feigns and fables it as lying external to the sphere of sense: and then, by referring our sensations to this unknown cause, he will obtain for them, not certainly the externality desiderated, but a quasi-externality, which he palms off upon himself and us as the best that can be supplied. This man is a Cosmothetical Idealist: that is, an Idealist who postulates an external universe as the unknown cause of certain modifications we are conscious of within ourselves, and which, according to his view, we never really get beyond. This species of speculator is the commonest, but he is the least trustworthy of any; and his fallacies are all the more dangerous by reason of the air of plausibility with which they are invested. From first to last, he represents us as the dupes of our own perfidious nature. By some inexplicable process of association, he refers certain known effects to certain unknown causes; and would thus explain to us how these effects (our sensations) come to assume, as it were, the character of external objects. But we know not "as it were." Away with such shuffling phraseology. There is nothing either of reference, or of inference, or of quasi- truthfulness in our apprehension of the material universe. It is ours with a certainty which laughs to scorn all the deductions of logic, and all the props of hypothesis. What we wish to know is, how our subjective affections can be, not as it were, but in God's truth, and In the strict, literal, earnest, and unambiguous sense of the words, real independent, objective existences. This is what the cosmothetical idealist never can explain, and never attempts to explain.
4. We now come to the answer which the reader, who has followed us thus far, will be prepared to find us putting forward as by far the most important of any, and as containing in fact the very kernel of the solution. A fourth man will say—"If the whole sphere of sense could only be withdrawn inwards—could be made to fall somewhere within itself—then the whole difficulty would disappear, and the problem would be solved at once. The sensations which existed previous to this retraction or withdrawal, would then, of necessity, fall without the sphere of sense, (see our second diagram;) and in doing so, they would necessarily assume a totally different aspect from that of sensations. They would be real independent objects: and (what is the important part of the demonstration) they would acquire this status without overstepping by a hair's-breadth the primary limits of the sphere. Were such phraseology allowable, we should say that the sphere has understepped itself, and in doing so, has left its former contents high and dry, and stamped with all the marks which can characterize objective existences."
Now the reader will please to remark, that we are very far from desiring him to accept this last solution at our bidding. Our method, we trust, is any thing but dogmatical. We merely say, that if this can be shown to be the case, then the demonstration which we are in the course of unfolding, will hardly fail to recommend itself to his acceptance. Whether or not it is the case, can only be established by an appeal to our experience.
We ask, then—does experience inform us, or does she not, that the sphere of sense falls within, and very considerably within, itself? But here it will be asked—what meaning do we attach to the expression, that sense falls within its own sphere? These words, then, we must first of all explain. Every thing which is apprehended as a sensation—such as colour, figure, hardness, and so forth—falls within the sentient sphere. To be a sensation, and to fall within the sphere of sense, are identical and convertible terms. When, therefore, it is asked does the sphere of sense ever fall within itself? this is equivalent to asking—do the senses themselves ever become sensations? Is that which apprehends sensations ever itself apprehended as a sensation? Can the senses be seized on within the limits of the very circle which they prescribe? If they cannot, then it must be admitted that "the sphere of sense never falls within itself, and consequently that an objective reality—i.e. a reality extrinsic to that sphere—can never be predicated or secured for any part of its contents. But we conceive that only one rational answer can be returned to this question. Does not experience teach us, that much if not the whole of our sentient nature becomes itself in turn a series of sensations? Does not the sight—that power which contains the whole visible space, and embraces distances which no astronomer can compute—does it not abjure its high prerogative, and take rank within the sphere of sense—itself a sensation—when revealed to us in the solid atom we call the eye? Here it is the touch which brings the sight within, and very far within, the sphere of vision. But somewhat less directly, and by the aid of the imagination, the sight operates the same introtraction (pardon the coinage) upon itself. It ebbs inwards, so to speak, from all the contents that were given in what may be called its primary sphere. It represents itself, in its organ, as a minute visual sensation, out of, and beyond which, are left lying the great range of all its other sensations. By imagining the sight as a sensation of colour, we diminish it to a speck within the sphere of its own sensations; and as we now regard the sense as for ever enclosed within this small embrasure, all the other sensations which were its, previous to our discovery of the organ, and which are its still, are built up into a world of objective existence, necessarily external to the sight, and altogether out of it's control. All sensations of colour are necessarily out of one another. Surely, then, when the sight is subsumed under the category of colour—as it unquestionably is whenever we think of the eye—surely all other colours must, of necessity, assume a position external to it; and what more is wanting to constitute that real objective universe of light and glory in which our hearts rejoice?
We can, perhaps, make this matter still plainer by reverting to our old illustration. Our first exposition of the question was designed to exhibit a general view of the case, through the medium of a dead symbolical figure. This proved nothing, though we imagine that it illustrated much. Our second exposition exhibited the illustration in its application to the living sphere of sensation in general; and this proved little. But we conceive that therein was foreshadowed a certain procedure, which, if it can be shown from experience to be the actual procedure of sensation in detail, will prove all that we are desirous of establishing. We now, then, descend to a more systematic exposition. of the process which (so far as our experience goes, and we beg to refer the reader to his own) seems to be involved. in the operation of seeing. We dwell chiefly upon the sense of sight, because it is mainly through its ministrations that a real objective universe is given to us. Let the circle A be the whole circuit of vision. We may begin by calling it the eye, the retina, or what we will. Let it be provided with the ordinary complement of sensations—the colours X Y Z. Now, we admit that these sensations cannot be extruded beyond the periphery of vision; and yet we maintain that, unless they be made to fall on the outside of that periphery, they cannot become real objects. How is this difficulty—this contradiction—to be overcome? Nature overcomes it, by a contrivance as simple as it is beautiful. In the operation of seeing, admitting the canvass or background of our picture to be a retina, or what we will, with a multiplicity of colours depicted upon it, we maintain that we cannot stop here, and that we never do stop here. We invariably go on (such is the inevitable law of our nature) to complete the picture—that is to say, we fill in our own eye as a colour within the very picture which our eye contains—we fill it in as a sensation within the other sensations which occupy the rest of the field; and in doing so, we of necessity, by the same law, turn these sensations out of the eye; and they thus, by the same necessity, assume the rank of independent objective existences. We describe the circumference infinitely within the circumference; and hence all that lies on the outside of the intaken circle comes before us stamped with the impress of real objective truth. We fill in the eye greatly within the sphere of sight, (or within the eye itself, if we insist on calling the primary sphere by this name,) and the eye thus filled in is the only eye we know any thing at all about, either from the experience of sight or of touch. How this operation is accomplished, is a subject of but secondary moment; whether it be brought about by the touch, by the eye itself, or by the imagination, is a question which might admit of much discussion; but it is one of very subordinate interest. The fact is the main thing—the fact that the operation is accomplished in one way or another—the fact that the sense comes before itself (if not directly, yet virtually) as one of its own sensations—that is the principal point to he attended to; and we apprehend that this fact is now placed beyond the reach of controversy.
To put the case in another light. The following considerations may serve to remove certain untoward difficulties in metaphysics and optics, which beset the path, not only of the uninitiated, but even of the professors of these sciences.
We are assured by optical metaphysicians, or metaphysical opticians, that, in the operations of vision, we never get beyond the eye itself, or the representations that are depicted therein. We see nothing, they tell us, but what is delineated within the eye. Now, the way in which a plain man should meet this statement, is this—he should ask the metaphysician what eye he refers to. Do you allude, sir, to an eye which belongs to my visible body, and forms a small part of the same; or do you allude to an eye which does not belong to my visible body, and which constitutes no portion thereof? If the metaphysician should say, that he refers to an eye of the latter description, then the plain man's answer should be—that he has no experience of any such eye—that he cannot conceive it—that he knows nothing at all about it—and that the only eye which be ever thinks or speaks of, is the eye appertaining to, and situated within, the phenomenon which he calls his visible body. Is this, then, the eye which the metaphysician refers to, and which he tells us we never get beyond? If it be—why, then, the very admission that this eye is a part of the visible body, (and what else can we conceive the eye to be?) proves that we must get beyond it. Even supposing that the whole operation were transacted within the eye, and that the visible body were nowhere but within the eye, still the eye which we invariably and inevitably fill in as belonging to the visible body, (and no other eye is ever thought of or spoken of by us,) —this eye, we say, must necessarily exclude the visible body, and all other visible things, from its sphere. Or, can the eye (always conceived of as a visible thing among other visible things) again contain the very phenomenon (i.e. the visible body ) within which it is itself contained? Surely no one will maintain a position of such unparalleled absurdity as that.
The science of optics. in so far as it maintains, according to certain physiological principles, that in the operation of seeing we never get beyond the representations within the eye, is founded on the assumption, that the visible body has no visible eye belonging to it. Whereas we maintain, that the only eye that we have—the only eye we can form any conception of, is the visible eye that belongs to the visible body, as a part does to a whole; whether this eye be originally revealed to us by the touch, by the sight, by the reason, or by the imagination. We maintain, that to affirm we never get beyond this eye in the exercise of vision, is equivalent to asserting, that a part is larger than the whole, of which it is only a part—is equivalent to asserting, that Y, which is contained between X and Z, is nevertheless of larger compass than X and Z, and comprehends them both. The fallacy we conceive to be this, that the visible body can be contained within the eye, without the eye of the visible body also being contained therein. But this is a procedure, which no law, either of thought or imagination, will tolerate. If we turn the visible body, and all visible things, into the eye, we must turn the eye of the visible body also into the eye; a process which, of course, again turns the visible body, and all visible things, out of the eye. And thus the procedure eternally defeats itself. Thus the very law which appears to annihilate, or render impossible, the objective existence of visible things, as creations independent of the eye—this very law, when carried into effect with a thorough-going consistency, vindicates and establishes that objective existence, with a logical force, an iron necessity, which no physiological paradox can countervail.
We have now probably said enough to convince the attentive reader, that the sense of sight, when brought under its own notice as a sensation, either directly, or through the ministry of the touch or of the imagination, (as it is when revealed to us in its organ,) falls very far—falls almost infinitely within its own sphere. Sight, revealing itself as a sense, spreads over a span commensurate with the diameter of the whole visible space; sight, revealing itself as a sensation, dwindles to a speck of almost unappreciable insignificance, when compared with the other phenomena which fall within the visual ken. This speck is the organ, and the organ is the sentient circumference drawn inwards, far within itself, according to a law which (however unconscious we may be of its operation) presides over every act and exercise of vision—a law which, while it contracts the sentient sphere, throws, at the same time, into necessary objectivity every phenomenon that falls external to the diminished circle. This is the law in virtue of which subjective visual sensations are real visible objects. The moment the sight becomes one of its own sensations, it is restricted, in a peculiar manner, to that particular sensation. It now falls, as we have said, within its own sphere. Now, nothing more was wanting to make the other visual sensations real independent existences; for, quà sensations, they are all originally independent of each other, and the sense itself being now a sensation, they must now also be independent of it.
We now pass on to the consideration of the sense of touch.
Here precisely the same process is gone through which was observed to take place in the case of vision. The same law manifests itself here, and the same inevitable consequence follows, namely —that sensations are things—that subjective affections are objective realities. The sensation of hardness (softness, be it observed, is only an inferior degree of hardness, and therefore the latter word is the proper generic term to be employed)—the sensation of hardness forms the contents of this sense. Hardness, we will say, is originally a purely subjective affection. The question, then, is, how can this affection, without being thrust forth into a fictitious, transcendent, and incomprehensible universe, assume, nevertheless, a distinct objective reality, and be (not as it were, but in language of the most unequivocating truth) a permanent existence altogether independent of the sense? We answer, that this can take place only provided the sense of touch can be brought under our notice as itself hard. If this can be shown to take place, then (as all sensations which are presented to us in space necessarily exclude one another, are reciprocally out of each other) all other instances of hardness must of necessity fall as extrinsic to that particular hardness which the sense reveals to us as its own; and, consequently, all these other instances of hardness will start into being, as things endowed with a permanent and independent substance.
Now, what is the verdict of experience on the subject? The direct and unequivocal verdict of experience is, that the touch reveals itself to us as one of its own sensations. In the finger-points more particularly, and generally all over the surface of the body, the touch manifests itself not only as that which apprehends hardness, but as that which is itself hard. The sense of touch vested in one of its own sensations (our tangible bodies namely) is the sense of touch brought within its own sphere. It comes before itself as one sensation of hardness. Consequently all its other sensations of hardness are necessarily excluded from this particular hardness; and, falling beyond it, they are by the same consequence built up into a world of objective reality, of permanent substance, altogether independent of the sense, self-betrayed as a sensation of hardness.
But here it may be asked, If the senses are thus reduced to the rank of sensations, if they come under our observation as themselves sensations, must we not regard them but as parts of the subjective sphere; and though the other portions of the sphere may be extrinsic to these sensations, still, must not the contents of the sphere, taken as a whole, be considered as entirely subjective, i.e. as merely ours, and consequently must not real objective existence be still as far beyond our grasp as ever? We answer. No, by no means. Such a query implies a total oversight of all that experience proves to be the fact with regard to this matter. It implies that the senses have not been reduced to the rank of sensations—that they have not been brought under our cognizance as themselves sensations, and that they have yet to be brought there. It implies that vision has not been revealed to us as a sensation of colour in the phenomenon the eye—and that touch has not been revealed to us as a sensation of hardness in the phenomenon the finger. It implies, in short, that it is not the sense itself which has been revealed to us, in the one case as coloured, and in the other case as hard, but that it is something else which has been thus revealed to us. But it may still be asked, How do we know that we are not deceiving ourselves? How can it be proved that it is the senses, and not something else, which have come before us under the guise of certain sensations? That these sensations are the senses themselves, and nothing but the senses, may be proved in the following manner.
We bring the matter to the test or actual experiment. We make certain experiments, seriatim, upon each of the items that lie within the sentient sphere, and we note the effect which each experiment has upon that portion of the contents which is not meddled with. In the exercise of vision, for example, we remove a book, and no change is produced in our perception of a house; a cloud disappears, yet our apprehension of the sea and the mountains, and all other visible things, is the same as ever. We continue our experiments, until our test happens to be applied to one particular phenomenon, which lies, if not directly, yet virtually, within the sphere of vision. We remove or veil this small visual phenomenon, and a totally different effect is produced from those that took place when any of the other visual phenomena were removed or veiled. The whole landscape is obliterated. We restore this phenomenon—the whole landscape reappears: we adjust his phenomenon differently—the whole landscape becomes differently adjusted. From these experiments we find, that this phenomenon is by no means an ordinary sensation, but that it differs from all other sensations in this, that it is the sense itself appearing in the form of a sensation. These experiments prove that it is the sense itself, and nothing else, which reveals itself to us in the particular phenomenon the eye. If experience informed us that the particular adjustment of some other visual phenomenon (a book, for instance) were essential to our apprehension of all the other phenomena, we should, in the same way, be compelled to regard this book as our sense of sight manifested in one of its own sensations. The book would be to us what the eye now is: it would be our bodily organ: and no à priori reason can be shown why this might not have been the case. All that we can say is, that such is not the finding of experience. Experience points out the eye, and the eye alone, as the visual sensation essential to our apprehension of all our other sensations of vision, and we come at last to regard this sensation as the sense itself. Inveterate association leads us to regard the eye, not merely as the organ, but actually as the sense of vision. We find from experience how much depends upon its possession, and we lay claim to it as a part of ourselves, with an emphasis that will not be gainsaid.
An interesting enough subject of speculation would be, an enquiry into the gradual steps by which each man is led to appropriate his own body. No man's body is given him absolutely, indefeasibly, and at once, ex dono Dei. It is no unearned hereditary patrimony. It is held by no à priori title on the part of the possessor. The credentials by which its tenure is secured to him, are purely of an à posteriori character; and a certain course of experience must be gone through before the body can become his. The man acquires it, as he does originally all other property, in a certain formal and legalized manner. Originally, and in the strict legal as well as metaphysical idea of them, all bodies, living as well as dead, human no less than brute, are mere waifs—the property of the first finder. But the law, founding on sound metaphysical principles, very properly makes a distinction here between two kinds of finding. To entitle a person to claim a human body as his own, it is not enough that he should find it in the same way in which he finds his other sensations, namely, as impressions which interfere not with the manifestations of each other. This is not enough, even though, in the case supposed, the person should be the first finder. A subsequent finder would have the preference, if able to show that the particular sensations manifested es this human body were essential to his apprehension of all his other sensations whatsoever. It is this latter species of finding—the finding, namely, of certain sensations as the essential condition on which the apprehension of all other sensations depends; it is this finding alone which gives each man a paramount and indisputable title to that "treasure trove" which he calls his own body. Now, it is only after going through a considerable course of experience and experiment, that we can ascertain what the particular sensations are upon which all our other sensations are dependent. And therefore were we not right in saying, that a man's body is not given to him directly and at once, but that he takes a certain time, and must go through a certain process, to acquire it?
The conclusion which we would deduce from the whole of the foregoing remarks is, that the great law of living sensation, the rationale of sensation as a living process, is this, that the senses are not merely presentative—i.e. they not only bring sensations before us, but that they are self-presentative—i.e. they, moreover, bring themselves before us as sensations. But for this law we should never get beyond our mere subjective modifications; but in virtue of it we necessarily get beyond them; for the results of the law are, 1st, that we, the subject, restrict ourselves to, or identify ourselves with, the senses, not as displayed in their primary sphere, (the large circle A,) but as falling within their own ken as sensations, in their secondary sphere, (the small circle A.) This smaller sphere is our own bodily frame; and does not each individual look upon himself as vested in his own bodily frame? And 2dly, it is a necessary consequence of this investment or restriction, that every sensation which lies beyond the sphere of the senses, viewed as sensations, (i.e. which lies beyond the body,) must be, in the most unequivocal sense of the words, a real independent object. If the reader wants a name to characterise this system, he may call it the system of Absolute or thorough-going presentationism.
- We say "living," because every attempt hitherto made to explain sensation, has been founded on certain appearances manifested in the "dead" subject. By inspecting a dead carcass we shall never discover the principle of life; by inspecting a dead eye, or a camera obscura, we shall never discover the principle of vision. Yet, though there is no seeing in a dead eye, or in a camera obscura, optics deal exclusively with such inanimate materials; and hence the student who studies them will do well to remember, that optics are the science of vision, with the "fact" of vision left entirely out of the consideration.