On the other hand, the conclusion that Evolution, considered under its most abstract form, is a certain change in the arrangement of parts; and that the causes of this change can be expressed only in terms of Matter, Motion, and Force; may in critical minds raise the question—What are Matter, Motion, and Force? Referring back in thought to the reasonings contained in the chapter on “Ultimate Scientific Ideas;” and remembering how it was there shown that absolute knowledge of Matter, Motion, and Force, is impossible; some readers will perhaps conclude that any such interpretation as the one above proposed, must be visionary. It may be asked—How can a comprehensible account of Evolution be given in terms that are themselves incomprehensible? Before proceeding, this question must be met. There can be no sound philosophy without clearly defined terms; and as, on the meanings of the terms to be here used, doubts have probably been cast by the reasonings contained in the chapter referred to, such doubts must be removed. If, as was shown, our ideas of things do not correspond with things in themselves, it becomes necessary to inquire in what way they are to be accepted. If they are not absolutely true, then what is the exact meaning of the assertion that they are relatively true? To this question let us now address ourselves. CHAPTER V. SPACE, TIME, MATTER, MOTION, AND FORCE. § 61. That sceptical state of mind which the criticisms of Philosophy usually produce, is, in great measure, caused by the misinterpretation of words. A sense of universal illusion ordinarily follows the reading of metaphysics; and is strong in proportion as the argument has appeared conclusive. This sense of universal illusion would probably never have arisen, had the terms used been always rightly construed. Unfortunately, these terms have by association acquired meanings that are quite different from those given to them in philosophical discussions; and the ordinary meanings being unavoidably suggested, there results more or less of that dreamlike idealism which is so incongruous with our instinctive convictions. The word _phenomenon_ and its equivalent word _appearance_, are in great part to blame for this. In ordinary speech, these are uniformly employed in reference to visual perceptions. Habit, almost, if not quite, disables us from thinking of _appearance_ except as something seen; and though _phenomenon_ has a more generalized meaning, yet we cannot rid it of associations with _appearance_, which is its verbal equivalent. When, therefore, Philosophy proves that our knowledge of the external world can be but phenomenal—when it concludes that the things of which we are conscious are appearances; it inevitably arouses in us the notion of an illusiveness like that to which our visual perceptions are so liable in comparison with our tactual perceptions. Good pictures show us that the aspects of things may be