The Complete Aristotle (eng.)

existent, and that matter is not separable from the
contraries but its being is different, and that a single matter may
serve for colour and heat and cold.
    The same matter also serves for both a large and a small body.
This is evident; for when air is produced from water, the same
matter has become something different, not by acquiring an addition
to it, but has become actually what it was potentially, and, again,
water is produced from air in the same way, the change being
sometimes from smallness to greatness, and sometimes from greatness
to smallness. Similarly, therefore, if air which is large in extent
comes to have a smaller volume, or becomes greater from being
smaller, it is the matter which is potentially both that comes to
be each of the two.
    For as the same matter becomes hot from being cold, and cold
from being hot, because it was potentially both, so too from hot it
can become more hot, though nothing in the matter has become hot
that was not hot when the thing was less hot; just as, if the arc
or curve of a greater circle becomes that of a smaller, whether it
remains the same or becomes a different curve, convexity has not
come to exist in anything that was not convex but straight (for
differences of degree do not depend on an intermission of the
quality); nor can we get any portion of a flame, in which both heat
and whiteness are not present. So too, then, is the earlier heat
related to the later. So that the greatness and smallness, also, of
the sensible volume are extended, not by the matter’s acquiring
anything new, but because the matter is potentially matter for both
states; so that the same thing is dense and rare, and the two
qualities have one matter.
    The dense is heavy, and the rare is light. [Again, as the arc of
a circle when contracted into a smaller space does not acquire a
new part which is convex, but what was there has been contracted;
and as any part of fire that one takes will be hot; so, too, it is
all a question of contraction and expansion of the same matter.]
There are two types in each case, both in the dense and in the
rare; for both the heavy and the hard are thought to be dense, and
contrariwise both the light and the soft are rare; and weight and
hardness fail to coincide in the case of lead and iron.
    From what has been said it is evident, then, that void does not
exist either separate (either absolutely separate or as a separate
element in the rare) or potentially, unless one is willing to call
the condition of movement void, whatever it may be. At that rate
the matter of the heavy and the light, qua matter of them, would be
the void; for the dense and the rare are productive of locomotion
in virtue of this contrariety, and in virtue of their hardness and
softness productive of passivity and impassivity, i.e. not of
locomotion but rather of qualitative change.
    So much, then, for the discussion of the void, and of the sense
in which it exists and the sense in which it does not exist.
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10
    Next for discussion after the subjects mentioned is Time. The
best plan will be to begin by working out the difficulties
connected with it, making use of the current arguments. First, does
it belong to the class of things that exist or to that of things
that do not exist? Then secondly, what is its nature? To start,
then: the following considerations would make one suspect that it
either does not exist at all or barely, and in an obscure way. One
part of it has been and is not, while the other is going to be and
is not yet. Yet time-both infinite time and any time you like to
take-is made up of these. One would naturally suppose that what is
made up of things which do not exist could have no share in
reality.
    Further, if a divisible thing is to exist, it is necessary that,
when it exists, all or some of its parts must exist. But of time
some parts have been, while others have to be, and no part of it is
though it is divisible. For what is ‘now’ is not a part: a part is
a measure of the whole, which must be made up of parts. Time, on
the other hand, is not held to be made up of ‘nows’.
    Again, the ‘now’ which seems to bound the past and the
future-does it always remain one and the same or is it always other
and other? It is hard to say.
    (1) If it is always different and different, and if none of the
parts in time which are other and other are simultaneous (unless
the one contains and the other is contained, as the shorter