4. Plato's Theory of Matter. In Plato the permanent
Being insisted upon by Parmenides and the Pythag-
oreans found its place in the real and eternal Ideas
(forms, essences), while the flux of Heraclitus was repre-
sented in the becoming, opinion, and appearance of
the empirical realm, matter providing the crucial rela-
tion between the two. But matter was not permanently
actual as in Democritus: the material thing was “always
in a process of becoming and never really is” (Timaeus
27e-28a). Nor was material change mere locomotion,
but a radical generation and destruction of temporal
existents (cf. Laws X, 894a). Again, whereas for De-
mocritus matter and space were opposites, for Plato
they were identified, for the Receptacle, that “hardly
real” principle of which we can form only a “spurious
conception” (Timaeus 52b) at once provided an oc-
cupiable space and yet also was the Mother, impreg-
nated by the immaterial essences and providing the
very stuff of the Offspring. The Offspring was the
changing empirical object, a “moving image” of eternal
Forms, and its essentially temporal character again was
the product of the Receptacle. For Plato, then, unlike
Democritus, temporal dimensions were as constitutive
of material objects as spatial ones and it was impossible
neatly to distinguish the two. Even when the verbal
formulae sound quite similar, meanings are opposed,
for when Plato spoke of “necessity” it was not of
something following ineluctably from formal proper-
ties, but, contrarily, of resistance to the action of form.
“The creation is mixed, being made of necessity and
mind” and it was produced when “Mind, the ruling
power, persuaded,” and thus “got the better of [,]
necessity” (Timaeus 47e-48a). Indeed such necessity
was what was most essential to matter as Plato con-
ceived it. Persuaded by the logical considerations that
had earlier impressed Parmenides that changing em-
pirical objects could not be real, he posited eternal
and totally intelligible archtypes. But if these were the
real, whence the disparity of their sensible appearances
from them? Here Plato felt the need to introduce “a
third thing” (Timaeus 48e-49a) and, like Democritus,
to assert that in a certain sense non-being is (Sophist
241e); for both thinkers the argument seemed to re-
quire a principle contrary to full being. The “third
thing” for Plato was the obscurely known Receptacle;
it enabled him to account for imperfections in the
earthly and mortal spheres because the very function
he assigned to it was that of a principle of privation.
Forms were universal, absolute, eternal, omnipresent,
intelligible, harmonious, and perfect; their images in
matter were particular, relative, temporal, localized,
confused, discordant, and defective. For Plato, there-
fore, matter was precisely what resisted and debilitated
Form.
The foregoing account has deliberately emphasized
methodological parallels between Democritus and
Plato. It could be added that in both instances of
accounting for the experienced as a mixture of contrar-
ies one of the contraries was matter. The functions
assigned to it, however, as we have seen varied as
radically as “being” and “non-being.” Further, sharing
Democritus' judgment of the deceptiveness of sense
experience, Plato also saw philosophy as an emancipa-
tion from that illusion, but the contrast is more inter-
esting; for while by appearance Democritus meant the
surplus by which the epistemologically given exceeded
what was ontologically there, Plato meant the defi-
ciency by which it fell short. What distressed him was
the “very melancholy” possibility that men would
continue to live among diluted shadows and echoes
and never reach “truth and the knowledge of realities”
(Phaedo 90d).
In view of the foregoing contrasts it may seem sur-
prising that Plato nonetheless sketched out a hypothesis
of atomic structures (Timaeus 53c-58c). Certainly the
dialectical method and the doctrine of hierarchically
ordered Forms, to say nothing of his specific teachings
on the “world-soul” (Timaeus 34-37), indicated an
“organismic” disposition to explain parts in terms of
the whole rather than the reverse. His theory of atomic
elements was in fact a confirmation of his identification
of matter with spatiality and his preference for geo-
metrical structure over stuff as a principle of explana-
tion. He equated Empedocles' four elements with four
of the five regular convex solids Theaetetus had identi-
fied. He conceived of these solids as volumes bounded
by two sorts of plane triangles, the half (diagonally cut)
square and half equilateral triangle (cut from apex to
base) which could be recombined according to various
possible equations (Figure 1): for example, one liquid
atom (an icosahedron with one hundred twenty trian-
gles making up its surfaces) might be broken by the
action of fire or air into two atoms of air (octahedrons
with forty-eight surface triangles each, for a sum of
ninety-six) plus one atom of fire (a tetrahedron with
twenty-four surface triangles). Clearly so geometrical
a hypothesis of ordered kinds of bodies must be seen
as already an instance of Mind's “getting the better
of necessity.”
What remained most central to the Platonic view
of matter, however, was the principle of non-being,
the capacity of which to impede the teleology and
intelligibility of full Being nevertheless obliges us to
concede it a certain existence. It is almost an irony
that Max Jammer in his search for the origins of the
concept of mass—that most irreducible of material
characteristics—should uncover a trail to the Neo-
Platonic conception of the inertial passivity of matter.
Johannes Kepler, a millennium and a half later, still
found it appropriate to characterize as a “vice” the
property of matter: “plump and clumsy to move itself.”
