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On The Heavens   


and of all other things in which they have power in themselves to

cause movement, and also their alterations and reciprocal

transformations. It is obvious, then, that the greater part of the

inquiry into nature concerns bodies: for a natural substance is either

a body or a thing which cannot come into existence without body and

magnitude. This appears plainly from an analysis of the character of

natural things, and equally from an inspection of the instances of

inquiry into nature. Since, then, we have spoken of the primary

element, of its bodily constitution, and of its freedom from

destruction and generation, it remains to speak of the other two. In

speaking of them we shall be obliged also to inquire into generation

and destruction. For if there is generation anywhere, it must be in

these elements and things composed of them.

This is indeed the first question we have to ask: is generation a

fact or not? Earlier speculation was at variance both with itself

and with the views here put forward as to the true answer to this

question. Some removed generation and destruction from the world

altogether. Nothing that is, they said, is generated or destroyed, and

our conviction to the contrary is an illusion. So maintained the

school of Melissus and Parmenides. But however excellent their

theories may otherwise be, anyhow they cannot be held to speak as

students of nature. There may be things not subject to generation or

any kind of movement, but if so they belong to another and a higher

inquiry than the study of nature. They, however, had no idea of any

form of being other than the substance of things perceived; and when

they saw, what no one previously had seen, that there could be no

knowledge or wisdom without some such unchanging entities, they

naturally transferred what was true of them to things perceived.

Others, perhaps intentionally, maintain precisely the contrary opinion

to this. It has been asserted that everything in the world was subject

to generation and nothing was ungenerated, but that after being

generated some things remained indestructible while the rest were

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