After the same manner we must conceive, that it is the business of a natural philosopher to speculate concerning a vacuum, weather it is or not, and how it subsists, or what it is; just as concerning place: for it is attended with similar incredibility, and the belief in it is derived from the conceptions about it: for those who assert that there is a vacuum consider it as if it were a certain place and vessel. And it appears indeed to be full when it possesses the bulk which it is capable of receiving; but when it is deprived of this it is void: as if a vacuum, plenum, and place, were the same, but their essence not the same. It is necessary however to begin the speculation, assuming the assertions of those who say that there is a vacuum, and again of those who deny its existence; and in the third place we must consider common opinions concerning them. Those therefore who endeavour to show that there is not a vacuum, do not refute that which men wish to call a vacuum, but that which they erroneously assert, as Anaxagoras and others, who confute after this manner; for they demonstrate that air is something by twisting bladders, showing how strong the air is, and receiving it in clepsydrae. But men conceive that a vacuum is an interval in which there is no sensible body; and, fancying that all being is body, they say that is a vacuum in which in short there is nothing; and on this account, that what is full of air is a vacuum. Hence, it is not necessary to demonstrate that error is something; But that there is not an interval different from, and separate from bodies, and that it is not in energy, and does not pervade through every body, so that it is not continuous, as Democritus and Leucippus say, and many other physiologists, and that it is not anything beyond all body, since body is continuous. These, therefore do not meet the problem through the gate; but rather those who say that there is a vacuum. But one thing, indeed which they say is this, that if there is not a vacuum there will not be local motion; and this is lation and increase: for motion would not appear to subsist unless there were a vacuum; since that which is full cannot receive. And if it could receive, there would be two bodies in the same thing. Certainly on this hypothesis any number of bodies whatever, may subsist together; for the difference cannot be induced through which that which is asserted will not take place. But if this be possible the smallest may receive the greatest thing: for that which is great is many small things. So that if many equal things may be in the same thing, this also may be the case with many unequal things. Melissus, therefore, shows from these things that the universe is immovable: for if it were moved, it would be necessary says he, that there should be a vacuum; but a vacuum does not rank among beings. In one way, therefore, they thus show that there is a certain void. But in another way, because some things appear to come together, and to be compressed; just as they say that wine is received by tubs, together with bladders, as if the condensed body would enter into the inherent void spaces. Again, increase likewise appears to all men to be effected through a vacuum: for nutriment is a body; and it is impossible for two bodies to subsist together. They also adduce as an evidence, that which happens about ashes, which receive as much water as avoid vessel. The Pythagoreans also say that there is a vacuum; and that it enters into the heaven, as if the heaven respired from an infinite spirit. They likewise assert that a vacuum is that which distinguishes natures, as if a vacuum were a certain separation and distinction of things in a consequent order; and that this first subsists in numbers; since a vacuum gives distinction to their nature. So many, therefore, and such are nearly the arguments, from which some assert and others deny the existence of a vacuum.
