Man a Machine

by Julien Offray de La Mettrie

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.