The Complete Aristotle (eng.)

do not exist but are
contained by time some were, e.g. Homer once was, some will be,
e.g. a future event; this depends on the direction in which time
contains them; if on both, they have both modes of existence. As to
such things as it does not contain in any way, they neither were
nor are nor will be. These are those nonexistents whose opposites
always are, as the incommensurability of the diagonal always is-and
this will not be in time. Nor will the commensurability, therefore;
hence this eternally is not, because it is contrary to what
eternally is. A thing whose contrary is not eternal can be and not
be, and it is of such things that there is coming to be and passing
away.
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13
    The ‘now’ is the link of time, as has been said (for it connects
past and future time), and it is a limit of time (for it is the
beginning of the one and the end of the other). But this is not
obvious as it is with the point, which is fixed. It divides
potentially, and in so far as it is dividing the ‘now’ is always
different, but in so far as it connects it is always the same, as
it is with mathematical lines. For the intellect it is not always
one and the same point, since it is other and other when one
divides the line; but in so far as it is one, it is the same in
every respect.
    So the ‘now’ also is in one way a potential dividing of time, in
another the termination of both parts, and their unity. And the
dividing and the uniting are the same thing and in the same
reference, but in essence they are not the same.
    So one kind of ‘now’ is described in this way: another is when
the time is near this kind of ‘now’. ‘He will come now’ because he
will come to-day; ‘he has come now’ because he came to-day. But the
things in the Iliad have not happened ‘now’, nor is the flood
‘now’-not that the time from now to them is not continuous, but
because they are not near.
    ‘At some time’ means a time determined in relation to the first
of the two types of ‘now’, e.g. ‘at some time’ Troy was taken, and
‘at some time’ there will be a flood; for it must be determined
with reference to the ‘now’. There will thus be a determinate time
from this ‘now’ to that, and there was such in reference to the
past event. But if there be no time which is not ‘sometime’, every
time will be determined.
    Will time then fail? Surely not, if motion always exists. Is
time then always different or does the same time recur? Clearly
time is, in the same way as motion is. For if one and the same
motion sometimes recurs, it will be one and the same time, and if
not, not.
    Since the ‘now’ is an end and a beginning of time, not of the
same time however, but the end of that which is past and the
beginning of that which is to come, it follows that, as the circle
has its convexity and its concavity, in a sense, in the same thing,
so time is always at a beginning and at an end. And for this reason
it seems to be always different; for the ‘now’ is not the beginning
and the end of the same thing; if it were, it would be at the same
time and in the same respect two opposites. And time will not fail;
for it is always at a beginning.
    ‘Presently’ or ‘just’ refers to the part of future time which is
near the indivisible present ‘now’ (’When do you walk? ‘Presently’,
because the time in which he is going to do so is near), and to the
part of past time which is not far from the ‘now’ (’When do you
walk?’ ‘I have just been walking’). But to say that Troy has just
been taken-we do not say that, because it is too far from the
‘now’. ‘Lately’, too, refers to the part of past time which is near
the present ‘now’. ‘When did you go?’ ‘Lately’, if the time is near
the existing now. ‘Long ago’ refers to the distant past.
    ‘Suddenly’ refers to what has departed from its former condition
in a time imperceptible because of its smallness; but it is the
nature of all change to alter things from their former condition.
In time all things come into being and pass away; for which reason
some called it the wisest of all things, but the Pythagorean Paron
called it the most stupid, because in it we also forget; and his
was the truer view. It is clear then that it must be in itself, as
we said before, the condition of destruction rather than of coming
into being (for change, in itself, makes things depart from their
former condition),