The investigation of similar questions about the void, also, must be
held to belong to the physicist-namely whether it exists or not, and
how it exists or what it is-just as about place. The views taken of it
involve arguments both for and against, in much the same sort of
way. For those who hold that the void exists regard it as a sort of
place or vessel which is supposed to be "full" when it holds the
bulk which it is capable of containing, "void" when it is deprived
of that-as if "void" and "full" and "place" denoted the same thing,
though the essence of the three is different.

    We must begin the inquiry by putting down the account given by those
who say that it exists, then the account of those who say that it does
not exist, and third the current view on these questions.

    Those who try to show that the void does not exist do not disprove
what people really mean by it, but only their erroneous way of
speaking; this is true of Anaxagoras and of those who refute the
existence of the void in this way. They merely give an ingenious
demonstration that air is something--by straining wine-skins and
showing the resistance of the air, and by cutting it off in
clepsydras. But people really mean that there is an empty interval
in which there is no sensible body. They hold that everything which is
in body is body and say that what has nothing in it at all is void (so
what is full of air is void). It is not then the existence of air that
needs to be proved, but the non-existence of an interval, different
from the bodies, either separable or actual-an interval which
divides the whole body so as to break its continuity, as Democritus
and Leucippus hold, and many other physicists-or even perhaps as
something which is outside the whole body, which remains continuous.

    These people, then, have not reached even the threshold of the
problem, but rather those who say that the void exists.

    (1) They argue, for one thing, that change in place (i.e. locomotion
and increase) would not be. For it is maintained that motion would
seem not to exist, if there were no void, since what is full cannot
contain anything more. If it could, and there were two bodies in the
same place, it would also be true that any number of bodies could be
together; for it is impossible to draw a line of division beyond which
the statement would become untrue. If this were possible, it would
follow also that the smallest body would contain the greatest; for
"many a little makes a mickle": thus if many equal bodies can be
together, so also can many unequal bodies.

    Melissus, indeed, infers from these considerations that the All is
immovable; for if it were moved there must, he says, be void, but void
is not among the things that exist.

    This argument, then, is one way in which they show that there is a
void.

    (2) They reason from the fact that some things are observed to
contract and be compressed, as people say that a cask will hold the
wine which formerly filled it, along with the skins into which the
wine has been decanted, which implies that the compressed body
contracts into the voids present in it.

    Again (3) increase, too, is thought to take always by means of void,
for nutriment is body, and it is impossible for two bodies to be
together. A proof of this they find also in what happens to ashes,
which absorb as much water as the empty vessel.

    The Pythagoreans, too, (4) held that void exists and that it
enters the heaven itself, which as it were inhales it, from the
infinite air. Further it is the void which distinguishes the natures
of things, as if it were like what separates and distinguishes the
terms of a series. This holds primarily in the numbers, for the void
distinguishes their nature.

    These, then, and so many, are the main grounds on which people
have argued for and against the existence of the void.