It must not be supposed that their reasons for their theories were wholly empirical. The atomic
theory was revived in modern times to explain the facts of chemistry, but these facts were not
known to the Greeks. There was no very sharp distinction, in ancient times, between empirical
observation and logical argument. Parmenides, it is true, treated observed facts with contempt,
but Empedocles and Anaxagoras would combine much of their metaphysics with observations
on water-clocks and whirling buckets. Until the Sophists, no philosopher seems to have doubted
that a complete metaphysic and cosmology could be established by a combination of much
reasoning and some observation. By good luck, the atomists hit on a hypothesis for which, more
than two thousand years later, some evidence was found, but their belief, in their day, was none
the less destitute of any solid foundation. *
Like the other philosophers of his time, Leucippus was concerned to find a way of reconciling
the arguments of Parmenides with the obvious fact of motion and change. As Aristotle says: â€
Although these opinions [those of Parmenides] 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 pro-
* On the logical and mathematical grounds for the theories of the atomists, see Gaston
Milhaud, Les Philosophes Géomà ̈tres de la Grà ̈ce, Ch. IV.â
€
On Generation and Corruption, 325 a.