duce passing-away. Moreover, they act and suffer action whenever they chance to be in contact
(for there they are not one), and they generate by being put together and becoming intertwined.
From the genuinely one, on the other hand, there could never have come to be a multiplicity,
nor from the genuinely many a one: that is impossible."
It will be seen that there was one point on which everybody so far was agreed, namely that there
could be no motion in a plenum. In this, all alike were mistaken. There can be cyclic motion in
a plenum, provided it has always existed. The idea was that a thing could only move into an
empty place, and that, in a plenum, there are no empty places. It might be contended, perhaps
validly, that motion could never begin in a plenum, but it cannot be validly maintained that it
could not occur at all. To the Greeks, however, it seemed that one must either acquiesce in the
unchanging world of Parmenides, or admit the void.
Now the arguments of Parmenides against not-being seemed logically irrefutable against the
void, and they were reinforced by the discovery that where there seems to be nothing there is
air. (This is an example of the confused mixture of logic and observation that was common.)
We may put the Parmenidean position in this way: "You say there is the void; therefore the void
is not nothing; therefore it is not the void." It cannot be said that the atomists answered this
argument; they merely proclaimed that they proposed to ignore it, on the ground that motion is a
fact of experience, and therefore there must be a void, however difficult it may be to conceive. *
Let us consider the subsequent history of this problem. The first and most obvious way of
avoiding the logical difficulty is to distinguish between matter and space. According to this
view, space is not nothing, but is of the nature of a receptacle, which may or may not have any
given part filled with matter. Aristotle says ( Physics, 208 b): "The theory that the void exists
involves the existence of place: for
* Bailey (op. cit. p. 75) maintains, on the contrary, that Leucippus had an answer, which was
"extremely subtle." It consisted essentially in admitting the existence of something (the
void) which was not corporeal. Similarly Burnet says: "It is a curious fact that the
Atomists, who are commonly regarded as the great materialists of antiquity, were actually
the first to say distinctly that a thing might be real without being a body."