Thus it is easy to see that the Unconditioned exists only as a part of the idea of the Conditioned, the Unknowable as the foil of the Knowable; and the erecting of these mere privatives, these negatives, these shadows, into substances and realities, and then setting them up as impassable barriers to human thought, is one of the worst pieces of work that metaphysics has been guilty of. The like does not hold in true contrasts. Each of them has an existence as a positive,and[TN-3] is never lost in a zero of the other. The one is always thought in relation to the other. Examples of these are subject and object, absolute and relative, mind and matter, person and consciousness, time and space. When any one of these is thought, the other is assumed. It is vain to attempt their separation. Thus those philosophers who assert that all knowledge is relative, are forced to maintain this assertion, to wit, All knowledge is relative, is nevertheless absolute, and thus they falsify their own position. So also, those others who say all mind is a property of matter, assume in this sentence the reality of an idea apart from matter. Some have argued that space and time can be conceived independently of each other; but their experiments to show it do not bear repetition. All true contraries are universals. A universal concept is one of “maximum extension,” as logicians say, that is, it is without limit. The logical limitation of such a universal is not its negation, but its contrary, which is itself also a universal. The synthesis of the two can be in theory only, yet yields a real product. To illustrate this by a geometrical example, a straight line produced indefinitely is, logically considered, a universal. Its antithesis or true contrary is not a crooked line, as might be supposed, but the straight line which runs at right angles to it. Their synthesis is not the line which bisects their angle but that formed by these contraries continually uniting, that is, the arc of a circle, the genesis of which is theoretically the union of two such lines. Again, time can only be measured by space, space by time; they are true universals and contraries; their synthesis is _motion_, a conception which requires them both and is completed by them. Or again, the philosophical extremes of downright materialism and idealism are each wholly true, yet but half the truth. The insoluble enigmas that either meets in standing alone are kindred to those which puzzled the old philosophers in the sophisms relating to motion, as, for instance, that as a body cannot move where it is and still less where it is not, therefore it cannot move at all. Motion must recognise both time and space to be comprehensible. As a true contrary constantly implies the existence of its opposite, we cannot take a step in right reasoning without a full recognition of both.