RELATIVITY OF KNOWLEDGE, a philosophic term which was much used by the philosophers of the middle of the 19th century, and has since fallen largely into disuse. It deserves. explanation, however, not only because it has occupied so large a space in the writings of some great British thinkers, but also because the main question for which it stands is still matter of eager debate. We get at the meaning of the term most easily by considering what it is that "relativity" is opposed to. "Relativity" of knowledge is opposed to absoluteness or positiveness of knowledge. Now there are two senses in which knowledge may claim to be absolute. The knower may say, "I know this absolutely," or he may say, "I know this absolutely."
With the emphasis upon the "know" he asserts that his knowledge of the matter in question cannot be affected by anything whatever. "I know absolutely that two and two are four makes an assertion about the knower's intellectual state: he isconvinced that his certain knowledge of the result of adding two to two is independent of any other piece of knowledge. With the emphasis upon the object of knowledge," I know this ," we have the other sense of absoluteness of knowledge: it is an assertion that the knower knows the" this,"whatever it may be, in its essence or as it truly is in itself. The phrase" relativity of knowledge "has therefore two meanings: (a) that no portion of knowledge is absolute, but is always affected by its relations to other portions of knowledge; (b) that what we know are not absolute things in themselves, but things conditioned in their quality by our channels of knowledge. Each of these two propositions must command assent as soon as uncritical ignorance gives place to philosophic reflection; but each may be exaggerated, indeed has currently been exaggerated, into falsity. The simplest experience - a single note struck upon the piano - would not be what it is to us but for its relation by contrast or comparison with other experiences. This is true; but we may easily exaggerate it into a falsehood by saying that a piece of experience is entirely constituted by its relation to other experiences. Such an extreme relativity, as advocated by T. H. Green in the first chapter of his Prolegomena to Ethics, involves the absurdity that our whole experience is a tissue of relations with no points of attachment on which the relations depend. The only motive for advocating it is the prejudice of absolute idealism which would deny that sensation has any part whatever in the constitution of experience. As soon as we recognize the part of sensation, we have no reason to deny the common-sense position that each piece of experience has its own quality, which is modified indefinitely by the relations in which it stands.
The second sense of relativity, that which asserts the impossibility of knowing things except as conditioned by our perceptive faculties, is more important philosophically and has had a more interesting history. To apprehend it is really the first great step in philosophical education. The unphilosophical person assumes that a tree as he sees it is identical with the tree as it is in itself and as it is for other percipient minds. Reflection shows that our apprehension of the tree is conditioned by the sense-organs with which we have been endowed, and that the apprehension of a blind man, and still more the apprehension of a dog or horse, is quite different from ours. What the tree is in itself - that is, for a perfect intelligence - we cannot know, any more than a dog or horse can know what the tree is for a human intelligence. So far the relativist is on sure ground; but from this truth is developed the paradox that the tree has no objective existence at all and consists entirely of the conscious states of the perceiver. Observe the parallelism of the two paradoxical forms of relativity: one says that things are relations with nothing that is related; the other says that things are perceptive conditions with nothing objective to which the conditions apply. Both make the given nothing and the work of the mind everything.
To see the absurdity of the second paradox of relativity is easier than to refute it. If nothing exists but the conscious states of the perceiver, how does he come to think that there is an objective tree at all ? Why does he regard his conscious states as produced by an object ? And how does he come to imagine that there are other minds than his own ? In short, this kind of relativity leads straight to what is generally known as " the abyss of solipsism." But, like all the great paradoxes of philosophy, it has its value in directing our attention to a vital, yet much neglected, element of experience. We cannot avoid solipsism (q.v.) so long as we neglect the element of force or power. If, as Hegel asserted, our experience is all knowledge, and if knowledge is indefinitely transformed by the conditions of knowing, then we are tempted to regard the object as superfluous, and to treat our innate conviction that knowledge has reference to objects as a delusion which philosophical reflection is destined to dispel. The remedy for the paradox is to recognize that the foundation for our belief in the existence of objects is the force which they exercise upon us and the resistance which they offer to our will. What the tree is in regard to its specific qualities depends on what faculties we have for perceiving it. But, whatever specific qualities it may have, it will still exist as an object, so long as it comes into dynamic relations with our minds.
In the history of thought the relativity of knowledge as just described begins with Descartes, the founder of modern philosophy: the characteristic of modern philosophy is that it lays more stress upon the subjective than upon the objective side of experience. It is a mistake to refer it back to the Greeks. The maxim of Protagoras, for example, "Man is the measure of all things," has a different purpose; it was meant to point to the truth that man rather than nature is the primary object of human study: it is a doctrine of humanism rather than of relativism. To appreciate the relativistic doctrines we find in various thinkers we must take account of the use to which they were put. By Descartes the principle was used as an instrument of scepticism, the beneficent scepticism of pulling down medieval philosophy to make room for modern science; by Berkeley it was used to combat the materialists; by Hume in the cause of scepticism once more against the intellectual dogmatists; by Kant to prepare a justification for a noumenal sphere to be apprehended by faith; by J. S. Mill and Herbert Spencer to support their derivation of all our experience from sensation. It is in Mill's Examination of Sir William Hamilton's Philosophy that the classical statement of the Relativity of Knowledge is to be found. The second chapter of that book sets forth the various forms of the doctrine with admirable lucidity and precision, and gives many references to other writers.
For the sake of clearness it seems desirable to keep for the future the term "relativity of knowledge" to the first meaning explained above: for the second meaning it has been superseded in contemporary philosophizing by the terms "subjectivism," "subjective idealism," and, for its extreme form, "solipsism" (q.v.). (H. St.)