§ 2. The course of our ordinary experience, as well as our education in the rudiments of the sciences, has made us all familiar with the distinction between what really _is_ or _exists_ and what merely _appears_ to be. There is no opposition more thoroughly enshrined in the language and literature of civilised races than the contrast of _seeming_ with _reality_, of _substance_ with _show_. We come upon it alike in our study of the processes of nature and our experience of human character and purpose. Thus we contrast the seeming stability of the earth with its real motion, the seeming continuity and sameness of a lump of solid matter with the real discontinuity and variety of its chemical constituents, the seeming friendliness of the hypocritical self-seeker with his real indifference to our welfare. In all these cases the motive which leads us to make the distinction is the same, namely, the necessity to escape from the admission of a contradiction in experience. So long as our various direct perceptions are not felt to conflict with one another, we readily accept them all as equally real and valid, and no question arises as to their relative truth or falsehood. Were all our perceptions of this kind, there would be no need for the correction, by subsequent reflection, of our first immediate impressions about the nature of ourselves and the world; error would be a term of no meaning for us, and science would have no existence. But when two immediate perceptions, both apparently equally authenticated by our senses, stand in direct conflict with one another,[2] we cannot, without doing violence to the fundamental law of rational thinking, regard both as equally and in the same sense true. Unless we abandon once for all the attempt to reconcile the course of our experience with the demand of our intellect for consistency in thinking, we are driven to make a momentous distinction. We have to recognise that things are not always what they seem to be; what appears to us is, sometimes at any rate, not real, and what really is does not always appear. Of our two conflicting perceptions, only one at best can be a correct representation of the real course of things; one of them at least, and possibly both, must be mere seeming or appearance, and we are thus cast upon the problem which every science tries, in its own sphere and its own way, to solve: what part of our conceptions about the world gives us reality and what part only appearance?[3] It is because of the importance of these puzzles of immediate perception as stimulating to such scientific reflection that Plato and Aristotle called philosophy the child of Wonder, and it is because the processes of change present them in a peculiarly striking form that the problem of change has always been a central one in Metaphysics.