Everything, however, which is changed, is changed partly from accident, as when we say, that what is musical walks, because that walks to which the being musical is an accident; and partly because something belonging to this is ehanged, it is simply said to be changed; as for instance, sueh things as are said to be changed according to parts; for the body is healed, becattse the eye or the breast is healed; and these are parts of the whole body. But there is something which is neither moved according to accident, nor because something else of it is moved, but because it is itself first moved; and this is that which is moved by itself. According to a different motion, however, there is a different subject; as for instance, that which is changed according to quality, and the subject of change according to quality, which may be healed or heated is differen. The like also takes place in that which moves: for one thing moves according to accident; but another according to a part, because some one of its parts move; and another by itself primarily; as for instance, the physician heals, and the hand strikes. But since there is something which first moves, and there is also something which is moved; and farther still, time in which it is moved; and besides these, that from which, and that into which it is moved; (for all motion is from something and into something; since that is different which is first moved, and into which and from which it is moved; as for instance, wood, the hot and the cold: but of these one is that which, another, into which, and another, from which.) Since this is the case, it is evident that motion is in the wood, and not in the form: for neither form, nor place, nor any definite quantity, either moves or is moved; but there is· that which moves, and that which is moved, and that into which it is moved: for mutation is more denominated from that into which, than from that from which it is moved; and on this account, corruption is a mutation into nonbeing; though also that which is corrupted is changed from being; and generation is a mutation into being, though it should be from non-being. What motion, therefore, is, has been shown before. But forms, passive qualities, and the place into which things that are moved, are moved, are things immoveable; such, for instance, as science and heat. Some one, however, may doubt whether passive qualities are motions, and whiteness a passive quality: for in this case there will be a mutation into motion. But perhaps not whiteness is motion, but the becoming white. In those also there is a subsistence according to accident, according to a part according to another, and ptimarily and not according to another. Thus that which is whitened is changed into that which is intellectually apprehended, according to accident; for it happens to colour to be intellectually pereeived: but it is changed into colour, because the white is a part of colour. It is also changed in Europe because Athens is a part of Europe; but it is changed into a white colour essentially. Hence, it is manifest how a thing is moved essentially, how according to accident, and how according to something else; likewise how the same thing is first, as well in that which moves as in that which is moved; and also that motion is not in form, but in that which is moved and is moveable in energy. The mutation, therefore, which subsists according to accident we shall omit; for it is in all things and always, and of all things. But that which is not according to accident, is not in all things, but in contraries, in things which have au intermediate subsistence, and in contradiction; the truth of which is confirmed by induction. But from that which has an intermediate subsistence a thing is changed as from a contrary; for it uses it as that which is contrary to each extreme: for that which has an intermediate subsistence, is in a certain respect the extremes. Hence, this compared to those, and those to this, are said to be, in a certain respect, contraries. Thus the middle chord compared to the nete is fiat, and is sharp compared to the hypate. Thus also, the dark brown compared to the black is white, and compared to the white is black.
