All philosophers, therefore, make principles to be contraries as well those who say that the universe is one and does not move (for Parmenides makes principles to be the hot and the cold, and these he denominates fire and earth) as those who introduced as principles the rare and the dense. But Democritus makes principles to be the solid and the void, of which the former he says as the relation of being, but the latter of non-being. Besides this, he distinguishes the solid by position figure, and order, for these are the genera of contraries. By position, as upwards, downwards, behind, before. By figure as angular and without angles, straight and circular. That all philosophers, therefore, in a certain respect make principles to be contraries, is manifest. And it is reasonable that they should, for it is necessary that principles should neither be produced from each other, nor from other things, and that from these all things should be generated. But these requisites are inherent in the first contraries. For, because they are first, they are not from other things, and because they are contraries, they are not from each other. But, it is necessary to consider how it happens that all things originate from principles. In the first place, therefore, it must be assumed that in the universality of things nothing is naturally adapted to act casually upon anything, or to be casually acted upon by anything. Nor is anything disposed to be generated from anything, unless someone considers these things as taking place according to accident. For, how can that which is white be generated from that which is musical, unless the being musical happens to that which is white or black? But white is generated from that which is not white and this not from everything which is not white, but from black or some one of the intermediate colors. That which is musical also is generated from that which is not musical. Yet, not from everything which is not, but from that which is void of music, or something (if there be any such thing) which subsists between these. Neither is the thing corrupted into any casual first. Thus, for instance, white is not corrupted into that which is musical unless perhaps according to accident, but into that which is not white. And this not into anything not white which may occur, but into black or some intermediate color. In like manner, that which is musical is corrupted into that which is not musical, and this not into anything unmusical which may occur, but into that which is void of music, or into something between these, if there be any such thing. The like also takes place in other things because things which are not simple but composite subsist according to a similar reasoning. As, however, the opposite dispositions are not denominated, we are ignorant that this circumstance happens. For it is necessary that everything which is harmonized should be generated from that which is void of harmony, and that which is void of harmony from that which is harmonized. It is also necessary that what is harmonized should be corrupted into a privation of harmony, and this not casually, but into its opposite. But there is no difference whether this is asserted of harmony or of order or composition, for it is evident that the same reasoning will apply to all these. A house also a statue and anything else are generated after a similar manner. For a house is generated not from the particulars from which it is composed, being so composed as to form the house, but from there being separated; and a statue and anything which is figured or generated from a privation of figure and each of these is partly order and partly a certain composition. If therefore this is true, whatever is generated is generated from contraries, and whatever is corrupted is corrupted into contraries and into the media which subsist between these. But these media subsist from contraries, as, for instance, intermediate colors subsist from white and black. Hence, all things which are generated by nature are either contraries or from contraries. Thus far, therefore, nearly the ancient philosophers have advanced together with us, and most others, as we have before said. For all of them assert that the elements and those things which are called by them principles are contraries, though they establish them without reason. As if they were compelled to assert this by truth itself. They differ, however from each other in this, that some of them assume prior and others posterior principles, and some of them things more known according to reason, but others such as are more known according to sense. For some establish the hot and the cold, others the moist and the dry, others the odd and even, and others strife and friendship as the causes of generation. But these differ from each other in the manner above mentioned. Hence in a certain respect they assert the same things and speak differently from each other. They assert different things indeed, as is also apparent to most men, but the same things, so far as they speak analogously. For the assume principles from the same coordination; since of contraries some contain and others are contained. Hence they speak similarly and differently, and worse and better. And some indeed establish things more known according to reason, as we have observed; but others, such as are more known according to sense; for universal is known according to reason, but that which is particular according to sense; since universals are the objects of reason, but particulars of sins. Thus, for instance, the great and the small are more known according to reason, but the rare and the dense according to sense. That it is necessary therefore that principles should be contraries is evident.
