Arist. _de Caelo_, Γ, 1. 298 b 21, quoted above, p. 203, _n._ 449. That which is, is; and it cannot be more or less. There is, therefore, as much of it in one place as in another, and the world is a continuous, indivisible _plenum_. From this it follows at once that it must be immovable. If it moved, it must move into an empty space, and there is no empty space. It is hemmed in by _what is_, by the real, on every side. For the same reason, it must be finite, and can have nothing beyond it. It is complete in itself, and has no need to stretch out indefinitely into an empty space that does not exist. Hence, too, it is spherical. It is equally real in every direction, and the sphere is the only form which meets this condition. Any other would _be_ in one direction more than in another. And this sphere cannot even move round its own axis; for there is nothing outside of it with reference to which it could be said to move. [Sidenote: Parmenides the father of materialism.] 89. To sum up. What _is_, is a finite, spherical, motionless corporeal _plenum_, and there is nothing beyond it. The appearances of multiplicity and motion, empty space and time, are illusions. We see from this that the primary substance of which the early cosmologists were in search has now become a sort of “thing in itself.” It never quite lost this character again. What appears later as the elements of Empedokles, the so-called “homoeomeries” of Anaxagoras and the atoms of Leukippos and Demokritos, is just the Parmenidean “being.” Parmenides is not, as some have said, the “father of idealism”; on the contrary, all materialism depends on his view of reality. [Sidenote: The beliefs of “mortals.”]