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 time is by the
longer), and if the "now" which is not, but formerly was, must have
ceased-to-be at some time, the "nows" too cannot be simultaneous
with one another, but the prior "now" must always have ceased-to-be.
But the prior "now" cannot have ceased-to-be in itself (since it
then existed); yet it cannot have ceased-to-be in another "now". For
we may lay it down that one "now" cannot be next to another, any
more than point to point. If then it did not cease-to-be in the next
"now" but in another, it would exist simultaneously with the
innumerable "nows" between the two-which is impossible.

    Yes, but (2) neither is it possible for the "now" to remain always
the same. No determinate divisible thing has a single termination,
whether it is continuously extended in one or in more than one
dimension: but the "now" is a termination, and it is possible to cut
off a determinate time. Further, if coincidence in time (i.e. being
neither prior nor posterior) means to be "in one and the same
"now"", then, if both what is before and what is after are in this
same "now", things which happened ten thousand years ago would be
simultaneous with what has happened to-day, and nothing would be
before or after anything else.

    This may serve as a statement of the difficulties about the
attributes of time.

    As to what time is or what is its nature, the traditional accounts
give us as little light as the preliminary problems which we have
worked through.

    Some assert that it is (1) the movement of the whole, others that it
is (2) the sphere itself.

    (1) Yet part, too, of the revolution is a time, but it certainly
is not a revolution: for what is taken is part of a revolution, not
a revolution. Besides, if there were more heavens than one, the
movement of any of them equally would be time, so that there would
be many times at the same time.

    (2) Those who said that time is the sphere of the whole thought
so, no doubt, on the ground that all things are in time and all things
are in the sphere of the whole. The view is too naive for it to be
worth while to consider the impossibilities implied in it.

    But as time is most usually supposed to be (3) motion and a kind
of change, we must consider this view.

    Now (a) the change or movement of each thing is only in the thing
which changes or where the thing itself which moves or changes may
chance to be. But time is present equally everywhere and with all
things.

    Again, (b) change is always faster or slower, whereas time is not:
for "fast" and "slow" are defined by time-"fast" is what moves much in
a short time, "slow" what moves little in a long time; but time is not
defined by time, by being either a certain amount or a certain kind of
it.

    Clearly then it is not movement. (We need not distinguish at present
between "movement" and "change".)