"Exclude from what we have considered real all qualities constituted by relation, we find that none are left." "Abstract the many relations from the one thing and there is nothing.... Without the relations it would not exist at all."[11] "The single feeling is nothing real." "On the recognition of relations as constituting the _nature_ of ideas, rests the possibility of any tenable theory of their reality." Such quotations as these from the late T. H. Green[12] would be matters of curiosity rather than of importance, were it not that sensationalist writers themselves believe in a so-called 'Relativity of Knowledge,' which, if they only understood it, they would see to be identical with Professor Green's doctrine. They tell us that the relation of sensations to each other is something belonging to their essence, and that no one of them has an absolute content: "That, e.g., black can only be felt in contrast to white, or at least in distinction from a paler or a deeper black; similarly a tone or a sound only in alternation with others or with silence; and in like manner a smell, a taste, a touch, only, so to speak, _in statu nascendi_, whilst, when the stimulus continues, all sensation disappears. This all seems at first sight to be splendidly consistent both with itself and with the facts. But looked at more closely, it is seen that neither is the case."[13] The two leading facts from which the doctrine of universal relativity derives its wide-spread credit are these: 1) The _psychological fact_ that so much of our actual knowledge _is_ of the relations of things--even our simplest sensations in adult life are habitually referred to classes as we take them in; and 2) The _physiological fact_ that our senses and brain must have periods of change and repose, else we cease to feel and think.