bodily realisation of
them), there arises a question: How do ideas become matter? Plato gives
two different explanations. In the "Republic" he says that God, instead
of perpetually creating individual things, created a distinct type
(idea) for each thing, and from this type all objects of the class are
made. But in a later work, the "Timaeus," Plato takes another view of the
origin of the world. Types are conceived as having existed from all
eternity, and God, in fashioning cosmos out of chaos, fashioned it after
the model of these eternal types.

Plato's conception of heaven and earth as two distinct regions is
completed by his conception of the double nature of the soul; or,
rather, of two souls, one rational and the other sensitive. The
sensitive soul awakens the divine reminiscences of the rational soul;
and the rational soul, by detecting the One in the Many, preserves man
from the scepticism inevitably resulting from mere sense-knowledge.

Aristotle, who was born in 384 B.C., was Plato's pupil. He, however,
completely broke away from his master's theory. He maintained that
individual objects alone exist. But if only individual objects exist,
only by the senses can they be known; and if we have only
sense-knowledge, how can we arrive at the general truths on which both
philosophy and science are founded? This was the problem which had led
Plato to claim for ideas, or types of general truths, a higher origin
than the intermittent and varying data of the senses.

Aristotle held that it could be solved in a natural way without the
conception of an ideal world. In his view, ideas were obtained by
induction. Sensation is the basis of all knowledge. But we have another
faculty besides that of sensation; we have memory. Having perceived many
objects, we remember our perceptions, and this enables us to discern
wherein things differ and wherein they agree. Then, by means of the art
of induction, we arrive at ideas. Aristotle's theory of induction is
clearly explained by him: "Experience furnishes the principles of every
science. Thus astronomy is grounded on observation. For if we were to
observe properly the phenomena of the heavens, we might demonstrate the
laws which regulate them. The same applies to other sciences." Had he
always held before his eyes this conception of science, he would have
anticipated Bacon--he would have been the Father of Positive Science.
But he could not confine himself to experience, as there