ng a
statue. Hence arose the idea of the efficient cause. The Eleatics did
not recognize it, for they denied motion, and for them, therefore, no
cause of motion could be assumed. But Parmenides, Aristotle thinks,
wavered on this point, somehow allowing vaguely the existence of a
second cause, which he denominated the hot and the cold. The reference
is, of course, to the second part of the poem of Parmenides. Other
philosophers clearly assumed an efficient cause, for they thought that
one element, for example, fire, is more active, that is, more
productive of motion, than others. Empedocles certainly attained to
the idea of an efficient cause, for he named as moving forces, harmony
and discord, love and hate. Anaxagoras also, used Nous as a moving
force.

Formal causes had, perhaps, been recognized by the Pythagoreans, for
numbers are forms. But they straightway degraded the formal cause to
the level of a material cause by declaring that number is the stuff or
matter of which things are made. Plato alone clearly saw the necessity
for the formal cause, for formal causes are, as we have seen, the same
as Plato's Ideas. But Plato's philosophy contains only two of the four
causes, namely the material and the formal, for Plato made all things
out of matter and the Ideas. Since the Ideas have in them {273} no
principle of motion, Plato's system contains no efficient cause. As
for final causes, Plato had indeed the vague idea that everything is
for the sake of the Good, but he makes no use of this conception and
does not develop it. Final causes were introduced into philosophy by
Anaxagoras, whose doctrine of the world forming mind was assumed to
explain the design and purpose which the universe exhibits. But as his
system developed he forgot about this, and used the Nous merely as a
piece of mechanism to explain motion, thus letting it sink into
nothing more than an efficient cause.

In the result, Aristotle finds that all four causes have been
recognized in greater or lesser degrees by his predecessors, and this,
in his opinion, greatly reinforces his own doctrine. But whereas
material and efficient causes have been clearly understood, his
predecessors had only vaguely foreshadowed and dimly perceived the
value of formal and final causes.

The next step in Aristotle's metaphysics is to reduce these four
principles to two, which he calls matter and form. This reduction
takes place by showing that formal cause, efficient ca