Relativity of Knowledge. The doctrine of the relativity of knowledge is almost a commonplace in some philosophical schools, and is as strenuously denied by others. It is connected primarily with the contrast between the absolute and the relative, or the noumenon and phenomenon, and is one phase of the great discussion as to the relation of knowledge to reality. In its modern form the doctrine has obtained currency chiefly through the speculations of Kant, Hamilton, and Mr Herbert Spencer. Knowledge evidently implies a knower and a relation between the knower and the object known. Hence it is argued that the object is conditioned by the relation into which it is brought; merely by becoming an object the thing as it is in itself undergoes a change or accommodation. Our knowledge therefore can never yield us the reality of things—the noumenon or thing-in-itself—but only the phenomenon, the thing as it appears to us. Or, as it is otherwise expressed, in being known the object must conform to the nature of the knowing faculty, the mental constitution or organisation of the knower; we cannot, therefore, conclude, says Hamilton, that the properties of existence are known 'in their native purity and without addition or modification from our organs of sense, or our capacities of intelligence.' Hamilton's general conclusion is: 'Of things absolutely or in themselves, be they external or be they internal, we know nothing, or know them only as incognisable; and we become aware of their incomprehensible existence only as this is indirectly or accidentally revealed to us, through certain qualities related to our faculties of knowledge. All that we know is therefore phenomenal, phenomenal of the unknown.' This is adopted by Mr Spencer, and made the basis of his theory of knowledge, or rather of what Ferrier would have called his agnoiology, his doctrine of our necessary ignorance: 'The reality existing behind all appearances is, and must ever be, unknown.' In Kant a similar doctrine is associated with the asserted subjectivity of the forms of space and time; but it is also based upon the broader consideration that perception can give us 'only the relation of an object to the subject, not the inward essence which belongs to the object in itself.' The empirical schools, which resolve our knowledge into impressions of sense manipulated according to the laws of association, likewise accept in its widest sense, as J. S. Mill points out, the doctrine of 'the entire inaccessibility to our faculties of any other knowledge of things than that of the impressions which they produce in our mental consciousness.' But, inasmuch as they in many cases profess a sceptical idealism which denies, or leaves doubtful, the existence of any reality beyond the states of consciousness, their views are less usually associated with the term.
The starting-point of the above argument must be conceded by all. Knowledge obviously implies relation; it exists only through the duality of knower and known, this duality being as necessarily present in the case of what is called self-knowledge as in the case of knowledge by self of independent objects. But the upholders of the doctrine of relativity proceed to convert this essential feature of intelligence into a proof of the 'importance' of our faculties. For the term is used in such a way as to imply a taint or defect in our knowledge. Our knowledge is condemned because it fails to realise a certain ideal. The question arises, however, whether the ideal proposed is in any sense legitimate or possible. What is this 'reality existing behind all appearances,' this thing in itself that so persistently evades our grasp? The answer of a sound philosophy would seem to be that this unknown essence or noumenal reality is a fictitious entity of our own creation. The essence or nature of a thing is expressed in its qualities or action; the noumenon reveals itself in the phenomenon. The relativists are in the habit of saying that 'we know only phenomena,' thus making our knowledge of phenomena the ground of our ignorance of the corresponding noumena. But, strictly speaking, it is a misuse of language to say that we know phenomena; the phenomenon is our knowledge of the noumenon. To say that we know phenomena is therefore only a roundabout way of saying that we know, and what we know is the noumenon or thing-in-itself. Of course the contrast between knowing and being is not abolished according to this view; in human knowledge, at all events, the existence of objects is independent of our knowledge of them. It is this contrast between the thing as existent and the thing as known that lends plausibility to the doctrine of relativity. But the contrast only justifies us in saying that knowing a thing is not the same as being that thing; whereas the relativistic doctrine says that, ipso facto, to know a thing is not to know the reality of the thing. Knowledge, in this view, infallibly cuts us off from knowing.
Apart from this general line of thought, the doctrine is frequently based upon the large extent to which sensation enters into all our knowledge. In the structure of their sense-organs different living creatures differ appreciably, and there will be a corresponding difference in the image of the world which they make to themselves. The knowledge of every being, it is argued, is thus inevitably conditioned by its organisation, and there is no possibility of arriving at an objective criterion. Man, in the Protagorean formula, is the measure of all things; but he measures them only as they seem to him. Such a formula may be interpreted either in a sensationalistic and individualistic fashion, as seems to have been done by Protagoras, or in a rationalistic and humanistic fashion, as is seen in Kant. The former interpretation leads to a sceptical dissolution of knowledge, for it leaves no common ground on which individuals might meet. Kant, by making space and time, if not the categories also, forms peculiar to the human intelligence, but common to all men, provides for objective truth between man and man, but insists on the merely human and relative character of such truth. Apart from the assertion of the merely subjective character of space and time, which Kant can hardly be said to have proved, it is evident that the relativist argument applies with most force to what are called the secondary qualities, such as tastes, smells, sounds, and colours. But when we consider the elevated pleasures of which the last two, at all events, are the source, we may well hesitate about pressing the relativistic argument too far. Things do not exist on their own account as bald brute facts, on which intelligence afterwards supervenes, to make what use of them it can. It seems truer to believe that to be known and enjoyed by spiritual beings is the purpose of their existence. The relativity of the world to the human senses and intellect would then form no ground for believing that the image of the world thus obtained was in any sense distorted or untrue. We may rise to higher insight and more perfect æsthetic appreciation, but that our know- ledge is finite and subject to revision does not deprive it of validity or objective truth in its own time and place. The case for the relativity of knowledge will be found strongly put in Sir W. Hamilton's Discussions and Lectures on Metaphysics, in Dean Mansel's Bampton Lectures, and in Mr Herbert Spencer's First Principles.