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CHAPTER II: The Relativity of Human Knowledge - John Stuart Mill, The Collected Works of John Stuart Mill, Volume IX - An Examination of William Hamilton’s Philosophy 
The Collected Works of John Stuart Mill, Volume IX - An Examination of William Hamilton’s Philosophy and of The Principal Philosophical Questions Discussed in his Writings, ed. John M. Robson, Introduction by Alan Ryan (Toronto: University of Toronto Press, London: Routledge and Kegan Paul, 1979).
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The Relativity of Human Knowledge
the doctrine which is thought to belong in the most especial manner to Sir W. Hamilton, and which was the ground of his opposition to the transcendentalism of the later French and German metaphysicians, is that which he and others have called the Relativity of Human Knowledge. It is the subject of the most generally known, and most impressive, of all his writings,[*] the one which first revealed to the English metaphysical reader that a new power had arisen in philosophy; and, together with its developments, it composes the “Philosophy of the Conditioned,” which he opposed to the German and French philosophies of the Absolute, and which is regarded by most of his admirers as the greatest of his titles to a permanent place in the history of metaphysical thought.
But the “relativity of human knowledge,” like most other phrases into which the words relative or relation enter, is vague, and admits of a great variety of meanings. In one of its senses, it stands for a proposition respecting the nature and limits of our knowledge, in my judgment true, fundamental, and full of important consequences in philosophy. From this amplitude of meaning its significance shades down through a number of gradations, successively more thin and unsubstantial, till it fades into a truism leading to no consequences, and hardly worth enunciating in words. When, therefore, a philosopher lays great stress upon the relativity of our knowledge, it is necessary to cross-examine his writings, and compel them to disclose in which of its many degrees of meaning he understands the phrase.
There is one of its acceptations, which, for the purpose now in view, may be put aside, though in itself defensible, and though, when thus employed, it expresses a real and important law of our mental nature. This is, that we only know anything, by knowing it as distinguished from something else; that all consciousness is of difference; that two objects are the smallest number required to constitute consciousness; that a thing is only seen to be what it is, by contrast with what it is not. The employment of the proposition, that all human knowledge is relative, to express this meaning, is sanctioned by high authorities,* and I have no fault to find with that use of the phrase. But we are not concerned with it in the present case; for it is not in this sense, that the expression is ordinarily or intentionally used by Sir W. Hamilton; though he fully recognises the truth which, when thus used, it serves to express. In general, when he says that all our knowledge is relative, the relation he has in view is not between the thing known and other objects compared with it, but between the thing known and the mind knowing.
All language recognises a distinction between myself—the Ego—and a world, either material, or spiritual, or both, external to me, but of which I can, in some mode and measure, take cognizance. The most fundamental questions in philosophy are those which seek to determine what we are able to know of these external objects, and by what evidence we know it.
In examining the different opinions which are or may be entertained on this subject, it will simplify the exposition very much, if we at first limit ourselves to the case of physical, or what are commonly called material objects. These objects are of course known to us through the senses. By those channels and no otherwise do we learn whatever we do learn concerning them. Without the senses we should not know nor suspect that such things existed. We know no more of what they are, than the senses tell us, nor does nature afford us any means of knowing more. Thus much, in the obvious meaning of the terms, is denied by no one, though there are thinkers who prefer to express the meaning in other language.
There are, however, conflicting opinions as to what it is that the senses tell us concerning objects. About one part of the information they give, there is no dispute. They tell us our sensations. The objects excite, or awaken in us, certain states of feeling. A part, at least, of what we know of the objects, is the feelings to which they give rise. What we term the properties of an object, are the powers it exerts of producing sensations in our consciousness. Take any familiar object, such as an orange. It is yellow; that is, it affects us, through our sense of sight, with a particular sensation of colour. It is soft; in other words it produces a sensation, through our muscular feelings, of resistance overcome by a slight effort. It is sweet; for it causes a peculiar kind of pleasurable sensation through our organ of taste. It is of a globular figure, somewhat flattened at the ends: we affirm this on account of sensations that it causes in us, respecting which it is still in dispute among psychologists whether they originally came to us solely through touch and the muscles, or also through the organ of sight. When it is cut open, we discover a certain arrangement of parts, distinguishable as being, in certain respects, unlike one another; but of their unlikeness we have no measure or proof except that they give us different sensations. The rind, the pulp, the juice, differ from one another in colour, in taste, in smell, in degree of consistency (that is, of resistance to pressure) all of which are differences in our feelings. The parts are, moreover, aoutsidea one another, occupying different portions of space: and even this distinction, it is maintained (though the doctrine is vehemently protested against by some) may be resolved into a difference in our sensations. When thus analysed, it is affirmed that all the attributes which we ascribe to objects, consist in their having the power of exciting one or another variety of sensation in our minds; that to us the properties of an object have this and no other meaning; that an object is to us nothing else than that which affects our senses in a certain manner; that we are incapable of attaching to the word object, any other meaning; that even an imaginary object is but a conception, such as we are able to form, of something which would affect our senses in some new way; so that our knowledge of objects, and even our fancies about objects, consist of nothing but the sensations which they excite, or which we imagine them exciting, in ourselves.
This is the doctrine of the Relativity of Knowledge to the knowing mind, in the simplest, purest, and, as I think, the most proper acceptation of the words. There are, however, two forms of this doctrine, which differ materially from one another.
According to one of the forms, the sensations which, in common parlance, we are said to receive from objects, are not only all that we can possibly know of the objects, but are all that we have any ground for believing to exist. What we term an object is but a complex conception made up by the laws of association, out of the ideas of various sensations which we are accustomed to receive simultaneously. There is nothing real in the process but these sensations. They do not, indeed, accompany or succeed one another at random; they are held together by a law, that is, they occur in fixed groups, and a fixed order of succession: but we have no evidence of anything which, not being itself a sensation, is a substratum or hidden cause of sensations. The idea of such a substratum is a purely mental creation, to which we have no reason to think that there is any corresponding reality exterior to our minds. Those who hold this opinion are said to doubt or deny the existence of matter. They are sometimes called by the name Idealists, sometimes by that of Sceptics, according to the other opinions which they hold. They include the followers of Berkeley and those of Hume. Among recent thinkers, the acute and accomplished Professor Ferrier, though by a circuitous path, and expressing himself in a very different phraseology, seems to have arrived at essentially the same point of view. These philosophers maintain the Relativity of our knowledge in the most extreme form in which the doctrine can be understood, since they contend, not merely that all we can possibly know of anything is the manner in which it affects the human faculties, but that there is nothing else to be known; that affections of human or of some other minds are all that we can know to exist.
This, however, is far from being the shape in which the doctrine of the Relativity of our knowledge is usually held. To most of those who hold it, the difference between the Ego and the Non-Ego is not one of language only, nor a formal distinction between two aspects of the same reality, but denotes two realities, each bhaving a separate existenceb , and neither dependent on the other. In the phraseology borrowed from the Schoolmen by the German Transcendentalists, they regard the Noumenon as in itself a different thing from the Phænomenon, and equally real; many of them would say, much more real, being the permanent Reality, of which the other is but the passing manifestation. They believe that there is a real universe of “Things in Themselves,” and that whenever there is an impression on our senses, there is a “Thing in itself,” which is behind the phænomenon, and is the cause of it. But as to what this Thing is “in itself,” we, having no corgansc except our senses for communicating with it, can only know what our senses tell us; and as they tell us nothing but the impression which the thing makes upon us, we do not know what it is in itself at all. We suppose (at least these philosophers suppose) that it must be dsomethingd “in itself,” but all that we know it to be is merely relative to us, consisting in the power of affecting us in certain ways, or, as it is technically called, of producing Phænomena. External things exist, and have an inmost nature, but their inmost nature is inaccessible to our faculties. We know it not, and can assert nothing of it with a meaning. Of the ultimate Realities, as such, we know the existence, and nothing more. But the impressions which these Realities make on us—the sensations they excite, the similitudes, groupings, and successions of those sensations, or, to sum up all this in a common though improper expression, the representations generated in our minds by the action of the Things themselves—these we may know, and these are all that we can know respecting them. In some future state of existence it is conceivable that we may know more, and more may be known by intelligences superior to us. Yet even this can only be true in the same sense in which a person with the use of his eyes knows more than is known to one born blind, or in which we should know more than we do if we were endowed with two or three additional senses. We should have more sensations; phænomena would exist to us of which we have at present no conception; and we emighte know better than we now do, many of those which are within our present experience; for fiff the new impressions gwereg linked with the old, as the old are with one another, by uniformities of succession and coexistence, we should now have new marks indicating to us known phænomena in cases in which we should otherwise have been unaware of them. But all this additional knowledge would be, like that which we now possess, merely phænomenal. We should not, any more than at present, know things as they are in themselves, but merely an increased number of relations between them and us. And in the only meaning which we are able to attach to the term, all knowledge, by however exalted an Intelligence, can only be relative to the knowing Mind. If Things have an inmost nature, apart not only from the impressions which they produce, but from all those which they are fitted to produce, on any sentient being, this inmost nature is unknowable, inscrutable, and inconceivable, not to us merely, but to every other creature. To say that even the Creator could know it, is to use language which to us has no meaning, because we have no faculties by which to apprehend that there is any such thing for him to know.
It is in this form that the doctrine of the Relativity of Knowledge is held by the greater number of those who profess to hold it, attaching any definite idea to the term. These again are divided into several distinct schools of thinkers, by some of whom the doctrine is held with a modification of considerable importance.
Agreeing in the opinion that what we know of Noumena, or Things in themselves, is but their bare existence, all our other knowledge of Things being but a knowledge of something in ourselves which derives its origin from them; there is a class of thinkers who hold that our mere sensations, and an outward cause which produces them, do not compose the whole of this relative knowledge. The Attributes which we ascribe to outward things, or such at least as are inseparable from them in thought, contain, it is affirmed, other elements, over and above sensations plus an unknowable cause. These additional elements are still only relative, for they are not in the objects themselves, nor have we evidence of anything in the objects that answers to them. They are added by the mind itself, and belong, not to the Things, but to our perceptions and conceptions of them. Such properties as the objects can be conceived divested of, such as sweetness or sourness, hardness or softness, hotness or coldness, whiteness, redness, or blackness—these, it is sometimes admitted, exist in our sensations only. But the attributes of filling space, and occupying a portion of time, are not properties of our sensations in their crude state, neither, again, are they properties of the objects, nor is there in the objects any prototype of them. They result from the nature and structure of the Mind itself: which is so constituted that it cannot take any impressions from objects except in those particular modes. We see a thing in a place, not because the Noumenon, the Thing in itself, is in any place, but because it is the law of our perceptive faculty that we must see as in some place, whatever we see at all. Place is not a property of the Thing, but a mode in which the mind is compelled to represent it. Time and Space are only modes of our perceptions, not modes of existence, and higher Intelligences are possibly not bound by them. Things, in themselves, are neither in time nor in space, though we cannot represent them to ourselves except under that twofold condition. Again, when we predicate of a thing that it is one or many, a whole or a part of a whole, a Substance possessing Accidents, or an Accident inhering in a Substance—when we think of it as producing Effects, or as produced by a Cause, (I omit other attributes not necessary to be here enumerated,) we are ascribing to it properties which do not exist in the Thing itself, but with which it is clothed by the laws of our conceptive faculty—properties not of the Things, but of our mode of conceiving them. We are compelled by our nature to construe things to ourselves under these forms, but they are not forms of the Things. The attributes exist only in relation to us, and as inherent laws of the human faculties; but differ from Succession and Duration in being laws of our intellectual, not our sensitive faculty; technically termed Categories of the Understanding. This is the doctrine of the Relativity of our knowledge as held by Kant, who has been followed in it by many subsequent thinkers, German, English, and French.
By the side of this there is another philosophy, older in date, which, though temporarily eclipsed and often contemptuously treated by it, is, according to present appearances, likely to survive it. Taking the same view with Kant of the unknowableness of Things in themselves, and also agreeing with him that we mentally invest the objects of our perceptions with attributes which do not all point, like whiteness and sweetness, to specific sensations, but are in some cases constructed by the mind’s own laws; this philosophy, however, does not think it necessary to ascribe to the mind certain innate forms, in which the objects are (as it were) moulded into these appearances, but holds that Place, Extension, Substance, Cause, and the rest, are conceptions put together out of ideas of sensation by the known laws of association. This, the doctrine of Hartley, of James Mill, of Professor Bain, and other eminent thinkers, and which is compatible with either the acceptance or the rejection of the Berkeleian theory, is the extreme form of one mode of the doctrine of Relativity, as Kant’s is of another. Both schemes accept the doctrine in its widest sense—the entire inaccessibility to our faculties of any other knowledge of Things than that of the impressions which they produce in our mental consciousness.
Between these there are many intermediate systems, according as different thinkers have assigned more or less to the original furniture of the mind on the one hand, or to the associations generated by experience on the other. Brown, for example, regards our notion of Space or Extension as a product of association, while many of our intellectual ideas are regarded by him as ultimate and undecomposable facts. But he accepts, in its full extent, the doctrine of the Relativity of our knowledge, being of opinion that though we are assured of the objective existence of a world external to the mind, our knowledge of that world is absolutely limited to the modes in which we are affected by it. The same doctrine is very impressively taught by one of the acutest metaphysicians of recent times, Mr. Herbert Spencer, who, in his First Principles, insists with equal force upon the certainty of the existence of Things in Themselves, and upon their absolute and eternal relegation to the region of the Unknowable.* This is also, apparently, the doctrine of Auguste Comte: though while maintaining with great emphasis the unknowableness of Noumena by our faculties, his aversion to metaphysics prevented him from giving any definite opinion as to their real existence, which, however, his language always by implication assumes.[*]
It is obvious that what has been said respecting the unknowableness of Things “in themselves,” forms no obstacle to our ascribing attributes or properties to them, provided these are always conceived as relative to us. If a thing produces effects of which our sight, hearing, or touch can take cognizance, it follows, and indeed is but the same statement in other words, that the thing has power to produce those effects. These various powers are its properties, and of such, an indefinite multitude is open to our knowledge. But this knowledge is merely phænomenal. The object is known to us only in one special relation, namely, as that which produces, or is capable of producing, certain impressions on our senses; and all that we really know is these impressions. This negative meaning is all that should be understood by the assertion, that we cannot know the Thing in itself; that we cannot know its inmost nature or essence. The inmost nature or essence of a Thing is apt to be regarded as something unknown, which, if we knew it, would explain and account for all the phænomena which the thing exhibits to us. But this unknown something is a supposition without evidence. We have no ground for supposing that there is anything which if known to us would afford to our intellect this satisfaction; would sum up, as it were, the knowable attributes of the object in a single sentence. Moreover, if there were such a central property, it would not answer to the idea of an “inmost nature;” for if knowable by any intelligence, it must, like other properties, be relative to the intelligence which knows it, that is, it must hsolelyh consist in iproducing in that intelligence some specifically definite state of consciousnessi ; for this is the only idea we have of knowing; the only sense in which the verb “to know” means anything.
It would, no doubt, be absurd to assume that our words exhaust the possibilities of Being. There may be innumerable modes of it which are inaccessible to our faculties, and which consequently we are unable to name. But we ought not to speak of these modes of Being by any of the names we possess. These are all inapplicable, because they all stand for known modes of Being. We might invent new names for jsuchj unknown modes; but the new names would have no more meaning than the x, y, z, of Algebra. The only name we can give them which really expresses an attribute, is the word Unknowable.
The doctrine of the Relativity of our knowledge, in the sense which has now been explained, is one of great weight and significance, which impresses a character on the whole mode of philosophical thinking of whoever receives it, and is the key-stone of one of the only two possible systems of Metaphysics and Psychology. But the doctrine is capable of being, and is, understood in at least two other senses. In one of them, instead of a definite and important tenet, it means something quite insignificant, which no one ever did or could call in question. Suppose a philosopher to maintain that certain properties of objects are in the Thing, and not in our senses; in the thing itself, not as whiteness may be said to be in the thing (namely, that there is in the thing a power whereby it produces in us the sensation of white), but in quite another manner; and are known to us not indirectly, as the inferred causes of our sensations, but by direct perception of them in the outward object. Suppose the same philosopher nevertheless to affirm strenuously that all our knowledge is merely phænomenal, and relative to ourselves; that we do not and cannot know anything of outward objects, except relatively to our own faculties. I think our first feeling respecting a thinker who professed both these doctrines, would be to wonder what he could possibly mean by the latter of them. It would seem that he must mean one of two trivialities; either that we can only know what we have the power of knowing, or else that all our knowledge is relative to us inasmuch as it is we that know it.
There is another mode of understanding the doctrine of Relativity, intermediate between these insignificant truisms and the substantial doctrine previously expounded. The position taken may be, that perception of Things as they are in themselves is not entirely denied to us, but is so mixed and kconfoundedk with impressions derived from their action on us, as to give a relative character to the whole aggregate. Our absolute knowledge may be vitiated and disguised by the presence of a relative element. Our faculty (it may be said) of perceiving things as they are in themselves, though real, has its own laws, its own conditions, and necessary mode of operation: our cognitions consequently depend, not solely on the nature of the things to be known, but also on that of the knowing faculty, as our sight depends not solely upon the object seen, but upon that together with the structure of the eye. If the eye were not achromatic, we should see all visible objects with colours derived from the organ, as well as with those truly emanating from the object. Supposing, therefore, that Things in themselves are the natural and proper object of our knowing faculty, and that this faculty carries to the mind a report of what is in the Thing itself, apart from its effects on us, there would still be a portion of uncertainty in these reports, inasmuch as we could not be sure that the eye of our mind is achromatic, and that the message it brings from the Noumenon does not arrive tinged and falsified, in an unknown degree, through an influence arising from the necessary conditions of the mind’s action. We may, in short, be looking at Things in themselves, but through imperfect glasses: what we see may be the very Thing, but the colours and forms which the glass conveys to us may be partly an optical illusion. This is a possible opinion: and one who, holding this opinion, should speak of the Relativity of our knowledge, would not use the term wholly without meaning. But he could not, consistently, assert that all our knowledge is relative; since his opinion would be that we have a capacity of Absolute knowledge, but that we are liable to mistake relative knowledge for it.
In which, if in any, of these various meanings, was the doctrine of Relativity held by Sir W. Hamilton? To this question, a more puzzling one than might have been expected, we shall endeavour in the succeeding chapter to find an answer.
[[*] ]Discussions on Philosophy and Literature, Education and University Reform, 2nd ed. (London: Longman, Brown, Green, and Longmans; Edinburgh: Maclachlan and Stewart, 1853).
[* ]In particular by Mr. Bain, who habitually uses the phrase “relativity of knowledge” in this sense. [Cf., e.g., The Senses and the Intellect, 2nd ed. (London: Longman, Green, Longman, Roberts, and Green, 1864), pp. 9-10.]
[b-b]651, 652 self-existent
[c-c]651, 652 organ
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[f-f]651, 652 since
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[* ] [(London: Williams and Norgate), 1862. See, for possible illustration, Pt. I, Chap. iii (esp. concerning the Self), pp. 65-6, and Pt. II, Chap. i, pp. 127ff.] See, however, below, a note near the end of Chap. ix [pp. 143n-4n below].
[[*] ]See, e.g., Auguste Comte, Cours de philosophie positive, 6 vols. (Paris: Bachelier, 1830-42), Vol. I, pp. 4, 8; Vol. IV, p. 529.
[i-i]651, 652, 67 impressing that intelligence in some specific way
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