Is matter, in respect of alteration, an evil cause? It is thus proved that it is not more evil than good. For let the beginning of the change be from evil. Thus the change is from this to good through that which is indifferent. But let the alteration be from good. Again the beginning goes on through that which is indifferent. Whether the motion be to one extreme or to the other, the method is the same, and this is abundantly set forth. All motion has to do with quantity; but quality is the guide in virtue and vice. Now we know that these two are generically distinguished. But are God and matter alone principles, or does there remain anything else which is the mean between these two? For if there is nothing, these things remain unintermingled one with another. And it is well said that if the extremes are intermingled, there is a necessity for some thing intermediate to connect them. But if something else exists, it is necessary that that something be either body or incorporeal, and thus a third adventitious principle makes its appearance. First, therefore, if we suppose God and matter to be both entirely incorporeal, so that neither is in the other, except as the science of grammar is in the soul; to understand this of God and matter is absurd. But if, as in a vacuum, as some say, the vacuum is surrounded by this universe; the other, again, is without substance, for the substance of a vacuum is nothing. But if as accidents, first, indeed, this is impossible; for the thing that wants substance cannot be in any place; for substance is, as it were, the vehicle underlying the accident. But if both are bodies, it is necessary for both to be either heavy or light, or middle; or one heavy, and another light, or intermediate. If, then, both are heavy, it is plainly necessary that these should be the same, both among light things and those things which are of the middle sort; or if they alternate, the one will be altogether separate from the other. For that which is heavy has one place, and that which is middle another, and the light another. To one belongs the superior, to the other the inferior, and to the third the middle. Now in every spherical figure the inferior part is the middle; for from this to all the higher parts, even to the topmost superficies, the distance is every way equal, and, again, all heavy bodies are borne from all sides to it. Wherefore, also, it occurs to me to laugh when I hear that matter moving without order, -- for this belongs to it by nature, -- came to the region of God, or to light and brightness, and such-like. But if one be body, and the other incorporeal, first, indeed, that which is body is alone capable of motion. And then if they are not intermingled, each is separate from the other according to its proper nature. But if one be mixed up with the other, they will be either mind or soul or accident. For so only it happens that things incorporeal are mixed up with bodies.