There is apparently no reference to it in the authentic
writings of Plato. The physical writings of Aristotle,
however, are full of criticism and comment on the
Democritean theory, to which the Stagyrite is in the
main antagonistic. The two thinkers belong to radi-
cally different schools. The Athenian idealist school
dealt, as it is often scoffingly said, with words and
thoughts; the Abderite with things. The former tried
to analyze the laws of mind; the latter to explain the
origin and constitution of the physical world, the
world of external realities. Even when Aristotle does
deal with physics, he reduces reality to its logical
conception, and not to its mechanical constituents.

The scientific principles of Aristotle were in spirit,
if not in form, in contrast with those of modern
science. In him the physical view of causality was
subordinated to the logical conception of reason and
consequence. The cause, according to Aristotle,
was the reason why, not the antecedent. His doc-
trine of the four elements, long predominant in the
scientific world, started with a rough popular distinc-
tion as the basis of a physical system. In his theory
of motion he failed to separate the cause of motion
from the body which is moved; and he believed that
the body moved must be in mediate or immediate
contact with the body moving. He introduced
æsthetic considerations into his physical speculations,
and inferred that as circular motion is the most per-
fect and simple, it must be the original movement of
the universe. In one word, Aristotle was a teleologist.
He held to a unity or plan in nature which deter-

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