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On The Heavens   



present, since the matter of contraries is the same. Also, the

positive is prior to its privation (warm, for instance, to cold),

and rest and heaviness stand for the privation of lightness and

movement. But further, if fire and earth exist, the intermediate

bodies must exist also: each element stands in a contrary relation

to every other. (This, again, we will here take for granted and try

later to explain.) these four elements generation clearly is involved,

since none of them can be eternal: for contraries interact with one

another and destroy one another. Further, it is inconceivable that a

movable body should be eternal, if its movement cannot be regarded

as naturally eternal: and these bodies we know to possess movement.

Thus we see that generation is necessarily involved. But if so,

there must be at least one other circular motion: for a single

movement of the whole heaven would necessitate an identical relation

of the elements of bodies to one another. This matter also shall be

cleared up in what follows: but for the present so much is clear, that

the reason why there is more than one circular body is the necessity

of generation, which follows on the presence of fire, which, with that

of the other bodies, follows on that of earth; and earth is required

because eternal movement in one body necessitates eternal rest in

another.



4



The shape of the heaven is of necessity spherical; for that is the

shape most appropriate to its substance and also by nature primary.

First, let us consider generally which shape is primary among planes

and solids alike. Every plane figure must be either rectilinear or

curvilinear. Now the rectilinear is bounded by more than one line, the

curvilinear by one only. But since in any kind the one is naturally

prior to the many and the simple to the complex, the circle will be

the first of plane figures. Again, if by complete, as previously

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