However, before Descartes, some of the ancients made the essence of matter consist in solid extension. But this opinion, of which all the Cartesians have made much, has at all times been victoriously combated by clear reasons, which we will set forth later, for order demands that we first examine to what the properties of extension can be reduced. CHAPTER V. CONCERNING THE MOVING FORCE OF MATTER. 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.