On Generation and corruption
place allotted to it by the Order.
It is clear from what has been said (i) that coming-to-be and
passing-away actually occur, (ii) what causes them, and (iii) what
subject undergoes them. But (a) if there is to be movement (as we have
explained elsewhere, in an earlier work') there must be something
which initiates it; if there is to be movement always, there must
always be something which initiates it; if the movement is to be
continuous, what initiates it must be single, unmoved, ungenerated,
and incapable of 'alteration'; and if the circular movements are
more than one, their initiating causes must all of them, in spite of
their plurality, be in some way subordinated to a single
'originative source'. Further (b) since time is continuous, movement
must be continuous, inasmuch as there can be no time without movement.
Time, therefore, is a 'number' of some continuous movement-a 'number',
therefore, of the circular movement, as was established in the
discussions at the beginning. But (c) is movement continuous because
of the continuity of that which is moved, or because that in which the
movement occurs (I mean, e.g. the place or the quality) is continuous?
The answer must clearly be 'because that which is moved is
continuous'. (For how can the quality be continuous except in virtue
of the continuity of the thing to which it belongs? But if the
continuity of 'that in which' contributes to make the movement
continuous, this is true only of 'the place in which'; for that has
'magnitude' in a sense.) But (d) amongst continuous bodies which are
moved, only that which is moved in a circle is 'continuous' in such
a way that it preserves its continuity with itself throughout the
movement. The conclusion therefore is that this is what produces
continuous movement, viz. the body which is being moved in a circle;
and its movement makes time continuous.