Tahafut_al-Tahafut-transl-Engl-van-den-Bergh

impossibility in the former, and he deals with the act of the soul when it
imagines an increase in the one quantity which is assumed to be actual,
i.e. body, as if it concerned both quantities. This is a manifest error. For to
imagine an increase in actual spatial magnitude, so that it must end in
another actual spatial magnitude, is to imagine something which does not
exist in the essence and definition of spatial magnitude, but to imagine
priority and posteriority in a movement that occurs is to imagine something
that belongs to its essence. For a movement can only occur in time, i.e.
time has to pass beyond its beginning. For this reason one cannot
represent a time the initial term of which is not the final term of another
time, for the definition of ‘the instant’ is that it is the end of the past and the
beginning of the future,’ for the instant is the present which necessarily is
the middle between the past and the future, and to represent a present
which is not preceded by a past is absurd. This, however, does not apply
to the point, for the point is the end of the line and exists at the same time
as the line, for the line is at rest. Therefore one can imagine a point which
is the beginning of a line without its being the end of another line, but the
instant cannot exist without the past and tile future, and exists necessarily
after the past and before the future, and what cannot subsist in itself
cannot exist before the existence of the future without being the end of tile
past. The cause of this error is the comparison of the instant with the
point. The proof that each movement which occurs is preceded by time is
this: everything must come to exist out of a privation, and nothing can
become in the instant-of which it can be truly said that its becoming is a
vanishing-and so it must be true that its privation must be in another
moment than that in which it itself exists, and there is time between each
pair of instants, because instant is not continuous with instant, nor point
continuous with point. This has been proved in the sciences. Therefore
before the instant in which the movement occurs there must necessarily
be a time, because, when we represent two instants in reality, there must
necessarily be time between them.
And what is said in this objection that ‘higher’ resembles ‘before’ is not
true, nor does the instant resemble the point, nor the quantity which
possesses position the quantity which does not possess position.’ He who
allows the existence of an instant which is not a present, or of a present
which is not preceded by a past, denies time and the instant, for he
assumes an instant as having the description which we have mentioned,
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