case, say, when a statue is made out of a block of marble, the matter is the marble which lost its original form and assumed the form of a statue. In this case the marble, if you take away both the previous form and the present, will still have some form if it is still marble, for marble must have certain qualities if it is to be marble. In that case then the matter underlying the change in question is not pure matter, it is already endowed with some primitive form and is composite. But marble is ultimately reducible to the four elements, fire, air, water, earth, which are simpler; and theoretically, though not in practice, we can think away all form, and we have left only that which takes forms but is itself not any form. This is matter. Here the reader will ask, what kind of thing is it that has no form whatsoever, is it not nothing at all? How can anything exist without being a particular kind of thing, and the moment it is that it is no longer pure matter. Aristotle's answer is that it is true that pure matter is never found as an objective existence. Point to any real object and it is composed of matter and form. And yet it is not true that matter is a pure figment of the imagination; it has an existence of its own, a potential existence. And this leads us to another important conception in the Aristotelian philosophy. Potentiality and actuality are correlative terms corresponding to matter and form. Matter is the potential, form is the actual. Whatever potentialities an object has it owes to its matter. Its actual essence is due to its form. A thing free from matter would be all that it is at once. It would not be liable to change of any kind, whether progress or retrogression. All the objects of our experience in the sublunar world are not of this kind. They realize themselves gradually, and are never at any given moment all that they are capable of becoming. This is due to their matter. On the other hand, pure matter is _actually_ nothing. It is just capacity for being anything, and the moment it is anything it is affected with form. It is clear from this account that matter and form are the bases of sublunar life and existence. No change, no motion without matter and form. For motion is presupposed in all kinds of change. If then all processes of life and death and change of all kinds presuppose matter and form, the latter cannot themselves be liable to genesis and decay and change, for that would mean that matter is composed of matter and form, which is absurd. We thus see how Aristotle is led to believe in the eternity of matter and motion, in other words, the eternity of the world processes as we know them.