r
particular kind of matter. In fact, all form, all the specific
characters and {209} features of matter, as we know it, are due to the
operation of the Ideas. Hence matter as it is in itself, before the
image of the Ideas is stamped upon it, must be absolutely without
quality, featureless, formless. But to be absolutely without any
quality is to be simply nothing at all. This matter is, therefore, as
Plato says, absolute not-being. Zeller conjectures, probably rightly,
that what Plato meant was simply empty space. [Footnote 14] Empty
space is an existent not-being, and it is totally indeterminate and
formless. It accords with this view that Plato adopted the Pythagorean
tenet that the differential qualities of material substances are due
to their smallest particles being regular geometrical figures limited
out of the unlimited, that is, out of space. Thus earth is composed of
cubes. That is to say, empty space when bound into cubes (the limiting
of the unlimited) becomes earth. The smallest particles of fire are
_tetrahedra_, of air _octahedra_, of water _icosahedra_.

[Footnote 14: _Plato and the Older Academy_, chap. vii. ]

We have, then, on the one hand, the world of Ideas, on the other,
matter, an absolutely formless, chaotic, mass. By impressing the
images of the Ideas upon this mass, "things" arise, that is to say,
the specific objects of sense. They thus participate both in Being and
in not-being. But how is this mixing of Being and not-being brought
about? How do the Ideas come to have their images stamped upon matter?
It is at this point that we enter upon the region of myth. Up to this
point Plato is certainly to be taken literally. He of course believed
in the reality of the world of Ideas, and he no doubt also believed in
his principle of matter. And he thought that the objects of sense are
to be {210} explained as copies of the Ideas impressed upon matter.
But now, with the problem how this copying is brought about, Plato
leaves the method of scientific explanation behind. If the Ideas are
the absolute ground of all things, then the copying process must be
done by the Ideas themselves. They must themselves be made the
principles for the production of things. But this is, for Plato,
impossible. For production involves change. If the Ideas produce
things out of themselves, the Ideas must in the process undergo
change. But Plato has declared them to be absolutely unchangeable, and
to be thus immutable is t