Page:Early Greek philosophy by John Burnet, 3rd edition, 1920.djvu/357

Rh all explained in some other way. Aristotle distinctly declares that none of his predecessors had said anything of absolute weight and lightness. They had only treated of the relatively light and heavy.

This way of regarding the notions of weight and lightness is clearly formulated for the first time in Plato's Timaeus. There is no such thing in the world, we are told there, as "up" or "down." The middle of the world is not "down" but "just in the middle," and there is no reason why any point in the circumference should be said to be "above" or "below" another. It is really the tendency of bodies towards their kin that makes us call a falling body heavy and the place to which it falls "below." Here Plato is really giving the view taken more or less consciously by his predecessors, and it is not till the time of Aristotle that it is questioned. For reasons which do not concern us here, Aristotle identified the circumference of the heavens with "up" and the middle of the world with "down," and equipped the elements with natural weight and lightness that they might perform their rectilinear motions between them. As, however, Aristotle believed there was only one world, and did not ascribe weight to the heavens proper, the effect of this reactionary theory on his cosmical system was not great; it was only when Epicurus tried to combine it with the infinite void that its true character emerged. It seems to me that the nightmare of Epicurean atomism can only be explained on the assumption that an Aristotelian doctrine was violently adapted to a theory which really