For some of the older philosophers thought that 'what is' must of
necessity be 'one' and immovable. The void, they argue, 'is not':
but unless there is a void with a separate being of its own, 'what is'
cannot be moved-nor again can it be 'many', since there is nothing
to keep things apart. And in this respect, they insist, the view
that the universe is not 'continuous' but 'discretes-in-contact' is no
better than the view that there are 'many' (and not 'one') and a void.
For (suppose that the universe is discretes-in-contact. Then), if it
is divisible through and through, there is no 'one', and therefore
no 'many' either, but the Whole is void; while to maintain that it
is divisible at some points, but not at others, looks like an
arbitrary fiction. For up to what limit is it divisible? And for
what reason is part of the Whole indivisible, i.e. a plenum, and
part divided? Further, they maintain, it is equally necessary to
deny the existence of motion.
Reasoning in this way, therefore, they were led to transcend
sense-perception, and to disregard it on the ground that 'one ought to
follow the argument': and so they assert that the universe is 'one'
and immovable. Some of them add that it is 'infinite', since the limit
(if it had one) would be a limit against the void.
There were, then, certain thinkers who, for the reasons we have
stated, enunciated views of this kind as their theory of 'The
Truth'.... Moreover, although these opinions appear to follow
logically in a dialectical discussion, yet to believe them seems
next door to madness when one considers the facts. For indeed no
lunatic seems to be so far out of his senses as to suppose that fire
and ice are 'one': it is only between what is right and what seems
right from habit, that some people are mad enough to see no
difference.
Leucippus, however, thought he had a theory which harmonized with
sense-perception and would not abolish either coming-to-be and
passing-away or motion and the multiplicity of things. He made these
concessions to the facts of perception: on the other hand, he conceded
to the Monists that there could be no motion without a void. The
result is a theory which he states as follows: 'The void is a "not
being", and no part of "what is" is a "not-being"; for what "is" in
the strict sense of the term is an absolute plenum. This plenum,
however, is not "one": on the contrary, it is a many" infinite in
number and invisible owing to the minuteness of their bulk. The "many"
move in the void (for there is a void): and by coming together they
produce "coming to-be", while by separating they produce
"passing-away". Moreover, they act and suffer action wherever 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 never could have come-to-be
a multiplicity, nor from the genuinely-many a "one": that is
impossible. But' (just as Empedocles and some of the other
philosophers say that things suffer action through their pores, so)
'all "alteration" and all "passion" take place in the way that has
been explained: breaking-up (i.e. passing-away) is effected by means
of the void, and so too is growth-solids creeping in to fill the
void places.' Empedocles too is practically bound to adopt the same
theory as Leucippus. For he must say that there are certain solids
which, however, are indivisible-unless there are continuous pores
all through the body. But this last alternative is impossible: for
then there will be nothing solid in the body (nothing beside the
pores) but all of it will be void. It is necessary, therefore, for his
'contiguous discretes' to be indivisible, while the intervals
between them-which he calls 'pores'-must be void. But this is
precisely Leucippus' theory of action and passion.
Such, approximately, are the current explanations of the manner in
which some things 'act' while others 'suffer action'. And as regards
the Atomists, it is not only clear what their explanation is: it is
also obvious that it follows with tolerable consistency from the
assumptions they employ. But there is less obvious consistency in
the explanation offered by the other thinkers. It is not clear, for
instance, how, on the theory of Empedocles, there is to be
'passing-away' as well as 'alteration'. For the primary bodies of
the Atomists-the primary constituents of which bodies are composed,
and the ultimate elements into which they are dissolved-are
indivisible, differing from one another only in figure. In the
philosophy of Empedocles, on the other hand, it is evident that all
the other bodies down to the 'elements' have their coming-to-be and
their passingaway: but it is not clear how the 'elements'
themselves, severally in their aggregated masses, come-to-be and
pass-away. Nor is it possible for Empedocles to explain how they do
so, since he does not assert that Fire too (and similarly every one of
his other 'elements') possesses 'elementary constituents' of itself.