Two Conceptions of Vacuum

Abstract

Writers on ancient philosophy have always been impressed by the early atomists' conceptual breakthrough in introducing vacuum, or void, as an intelligible notion. But discussion of the concept itself has been rare and, on the whole, disappointing. It is as if the doctrine were so obviously correct and sensible that no one had paused to ask whether it really is quite so straightforward. My contention is that it raises considerable conceptual difficulties of its own, and that these gradually emerged, and were tackled, over a long period. I shall be concerned primarily with the theoretical aspects of void, and not with its cosmological role or with the empirical arguments for and against its existence. Void, To x?v6v, is literally 'the empty'. Does that mean empty space? So it is regularly assumed. In the index to Cyril Bailey's The Greek A tomists and Epicurus, for example, the entry under 'void' simply reads 'see space'. But there is, as a matter of Greek usage, at least one other thing that Tor xevov could mean, and that is 'emptiness'. Viewed as emptiness, void would not be a kind of space or place. Rather, a portion of void would be the emptiness in such and such a place. And as an occupier of place, it might even be considered capable of locomotion. There should be nothing intuitively abhorrent about the idea of something with a purely negative characterisation occupying places and moving a gap in the traffic, for example. When you carry your thermos flask to work, you would do well to think of the vacuum in it as moving from place to place with it. If you insist instead that the vacuum in it is empty space and therefore incapable of moving in space, you may have to conclude that throughout your journey the vacuum in your flask is being replaced in a constant stream. These considerations are not meant to tell decisively in favour of the space-occupier interpretation of void, but to show that that interpretation is not too implausible to be entertained. Whether or not a particular thinker actually adopts it, consciously or unconsciously, will depend partly on other features of his system. For example, if he considers void an element, capable of being part of a compound body and of moving around with it, he is more likely to think of it as a negative substance occupying