5. Kenon (“Void”). Early Pythagorean philosophy,
when still ingenuous, apparently identified space with
kenon (κενόν), which literally means “void.” In fact,
within his essay on the void in the Physica, Aristotle
has a passage about Pythagoreans which links kenon
with apeiron (“infinity”), pneuma (“breath”), ouranos
(“heaven”), and arithmos (“number”):
The Pythagoreans, too, held that the void exists and that
breath and void enter from the infinite into the heaven itself,
which as it were inhales; the void distinguishes the nature
of things, being a kind of separating and distinguishing
factor between terms in series. This happens primarily in
the case of numbers; for the void distinguishes their nature
(Physica 4, 6; 213b 22-28; Kirk and Raven, p. 252).
This fascinating report must be allowed to speak for
itself. Unlike some modern commentators, Aristotle,
very prudently, does not attempt to interpret it.
Otherwise, Aristotle's essay on the void in the
Physica suffers from an incurable weakness. As always
and everywhere, Aristotle maintains in this essay that
a void cannot exist, and in the present context Aristotle
would really like to give a general demonstration for
this thesis. But this he cannot do. Such a demonstration
would require that Aristotle first define his void
logically, and then argue metaphysically that it cannot
exist. However Aristotle finds it impossible to give a
logical definition of void that would not turn it into
a kind of space, or pseudo-space, or nonspace; and the
intended demonstration of his thesis dissolves into an
accumulation of remarks not easy to remember.
It is true that present-day physics is also unable to
define a void other than as a space devoid of matter
and energy, say. But this is of no harmful consequence
as long as nobody asserts, and wants to demonstrate,
that “a void cannot exist”; and nobody does.
