cease to prevent the earth's motion, where will the earth move to then? Its movement to the centre was constrained, and its rest at the centre is due to constraint; but there must be some motion which is natural to it.Will this be upward motion or downward or what? It must have some motion; and if upward and downward motion are alike to it, and the air above the earth does not prevent upward movement, then no more could air below it prevent downward movement.For the same cause must necessarily have the same effect on the same thing.
Further, against Empedocles there is another point which might be made.When the elements were separated off by Hate, what caused the earth to keep its place? Surely the 'whirl' cannot have been then also the cause.It is absurd too not to perceive that, while the whirling movement may have been responsible for the original coming together of the art of earth at the centre, the question remains, why now do all heavy bodies move to the earth.For the whirl surely does not come near us.Why, again, does fire move upward? Not, surely, because of the whirl.But if fire is naturally such as to move in a certain direction, clearly the same may be supposed to hold of earth.Again, it cannot be the whirl which determines the heavy and the light.
Rather that movement caused the pre-existent heavy and light things to go to the middle and stay on the surface respectively.Thus, before ever the whirl began, heavy and light existed; and what can have been the ground of their distinction, or the manner and direction of their natural movements? In the infinite chaos there can have been neither above nor below, and it is by these that heavy and light are determined.