THREE:We have seen how, for the antithesis between Form and Matter, was substituted the wider antithesis between Actuality and Possibility. Even in this latter the opposition is more apparent than real. A permanent possibility is only intelligible through the idea of its realisation, and sooner or later is certain to be realised. Aristotle still further bridges over the interval between them by a new conception��that of motion. Motion, he tells us, is the process of realisation, the transformation of power into act. Nearly the whole of his Physics is occupied with an enquiry into its nature and origin. As first conceived, it is equivalent to what we call change rather than348 to mechanical movement. The table of categories supplies an exhaustive enumeration of its varieties. These are, as we have already mentioned, alteration of quality or transformation, increase or decrease of quantity, equivalent to growth and decay, and transport from place to place. Sometimes a fourth variety is added, derived from the first category, substance. He calls it generation and destruction, the coming into existence or passing out of it again. A careful analysis shows that motion in space is the primordial change on which all others depend for their accomplishment. To account for it is the most vitally important problem in philosophy.It is well for the reputation of Aristotle that he could apply himself with such devotion to the arduous and, in his time, inglorious researches of natural history and comparative anatomy, since it was only in those departments that he made any real contributions to physical science. In the studies which were to him the noblest and most entrancing of any, his speculations are one long record of wearisome, hopeless, unqualified delusion. If, in the philosophy of practice and the philosophy of art, he afforded no real guidance at all, in the philosophy of Nature his guidance has312 always led men fatally astray. So far as his means of observation extended, there was nothing that he did not attempt to explain, and in every single instance he was wrong. He has written about the general laws of matter and motion, astronomy, chemistry, meteorology, and physiology, with the result that he has probably made more blunders on those subjects than any human being ever made before or after him. And, if there is one thing more astounding than his unbroken infelicity of speculation, it is the imperturbable self-confidence with which he puts forward his fallacies as demonstrated scientific certainties. Had he been right, it was no ��slight or partial glimpses of the beloved�� that would have been vouchsafed him, but the ��fullest and nearest revelation�� of her beauties. But the more he looked the less he saw. Instead of drawing aside he only thickened and darkened the veils of sense which obscured her, by mistaking them for the glorious forms that lay concealed beneath.