The ancients, persuaded that there is no body without a moving
force, regarded the substance of bodies as composed of two primitive
attributes. It was held that, through one of these attributes, this
substance has the capacity for moving and, through the other, the
capacity for being moved.{88} As a matter of fact, it is impossible
not to conceive these two attributes in every moving body, namely,
the thing which moves, and the same thing which is moved.
It has just been said that formerly the name, matter, was given to
the substance of bodies, in so far as it is susceptible of being
moved. When capable of moving this same matter was known by the name
of "active principle".... But these two attributes seem to depend so
essentially on each other that Cicero, in order better to state this
essential and primitive union of matter with its moving principle,
says that each is found in the other. This expresses very well the
idea of the ancients.
From this it is clear that modern writers have given us but an inexact
idea of matter in attempting (through a confusion ill understood)
to give this name to the substance of bodies. For, once more, matter,
or the passive principle of the substance of bodies, constitutes only
one part of this substance. Thus it is not surprising that these
modern thinkers have not discovered in matter moving force and the
faculty of feeling.
It should now be evident at the first glance, it seems to me, that
if there is an active principle it must have, in the unknown essence
of matter, another source than extension. This proves that simple
extension fails to give an adequate idea of the complete essence or
metaphysical form of the substance of bodies, and that this failure is
due solely to the fact that extension excludes the idea of any activity
in matter. Therefore, if we demonstrate this moving principle, if we
show that matter, far from being as indifferent as it is supposed
to be, to movement and to rest, ought to be regarded as an active,
as well as a passive substance, what resource can be left to those
who have made its essence consist in extension?
The two principles of which we have just spoken, extension and moving
force, are then but potentialities of the substance of bodies; for
in the same way in which this substance is susceptible of movement,
without actually being moved, it also has always, even when it is
not moving itself, the faculty of spontaneous motion.
The ancients have rightly noticed that this moving force acts in the
substance of bodies only when the substance is manifested in certain
forms; they have also observed that the different motions which it
produces are all subject to these different forms or regulated by
them. That is why the forms, through which the substance of bodies
can not only move, but also move in different ways, were called
material forms.
Once these early masters had cast their eyes on all the phenomena
of nature, they discovered in the substance of bodies, the power
of self-movement. In fact, this substance either moves itself, or
when it is in motion, the motion is communicated to it by another
substance. But can anything be seen in this substance, save the
substance itself in action; and if sometimes it seems to receive a
motion that it has not, does it receive that motion from any cause
other than this same kind of substance, whose parts act the one upon
the other?
If, then, one infers another agent, I ask what agent, and I demand
proofs of its existence. But since no one has the least idea of such
an agent, it is not even a logical entity. Therefore it is clear
that the ancients must have easily recognized an intrinsic force of
motion within the substance of bodies, since in fact it is impossible
to prove or conceive any other substance acting upon it.
Descartes, a genius made to blaze new paths and to go astray in them,
supposed with some other philosophers that God is the only efficient
cause of motion, and that every instant He communicates motion to all
bodies. But this opinion is but an hypothesis which he tried to adjust
to the light of faith; and in so doing he was no longer attempting
to speak as a philosopher or to philosophers. Above all he was not
addressing those who can be convinced only by the force of evidence.
The Christian Scholastics of the last centuries have felt the full
force of this reflection; for this reason they have wisely limited
themselves to purely philosophic knowledge concerning the motion of
matter, although they might have shown that God Himself said that He
had "imprinted an active principle in the elements of matter (Gen. i;
Is. lxvi)."
One might here make up a long list of authorities, and take from the
most celebrated professors the substance of the doctrine of all the
rest; but it is clear enough, without a medley of citations, that
matter contains this moving force which animates it, and which is
the immediate cause of all the laws of motion.