We may distinguish generally between predicating B of A because it
(A) is itself, and because it is something else; and particularly
between place which is common and in which all bodies are, and the
special place occupied primarily by each. I mean, for instance, that
you are now in the heavens because you are in the air and it is in the
heavens; and you are in the air because you are on the earth; and
similarly on the earth because you are in this place which contains no
more than you.

    Now if place is what primarily contains each body, it would be a
limit, so that the place would be the form or shape of each body by
which the magnitude or the matter of the magnitude is defined: for
this is the limit of each body.

    If, then, we look at the question in this way the place of a thing
is its form. But, if we regard the place as the extension of the
magnitude, it is the matter. For this is different from the magnitude:
it is what is contained and defined by the form, as by a bounding
plane. Matter or the indeterminate is of this nature; when the
boundary and attributes of a sphere are taken away, nothing but the
matter is left.

    This is why Plato in the Timaeus says that matter and space are
the same; for the "participant" and space are identical. (It is
true, indeed, that the account he gives there of the "participant"
is different from what he says in his so-called "unwritten
teaching". Nevertheless, he did identify place and space.) I mention
Plato because, while all hold place to be something, he alone tried to
say what it is.

    In view of these facts we should naturally expect to find difficulty
in determining what place is, if indeed it is one of these two things,
matter or form. They demand a very close scrutiny, especially as it is
not easy to recognize them apart.

    But it is at any rate not difficult to see that place cannot be
either of them. The form and the matter are not separate from the
thing, whereas the place can be separated. As we pointed out, where
air was, water in turn comes to be, the one replacing the other; and
similarly with other bodies. Hence the place of a thing is neither a
part nor a state of it, but is separable from it. For place is
supposed to be something like a vessel-the vessel being a
transportable place. But the vessel is no part of the thing.

    In so far then as it is separable from the thing, it is not the
form: qua containing, it is different from the matter.

    Also it is held that what is anywhere is both itself something and
that there is a different thing outside it. (Plato of course, if we
may digress, ought to tell us why the form and the numbers are not
in place, if "what participates" is place-whether what participates is
the Great and the Small or the matter, as he called it in writing in
the Timaeus.)

    Further, how could a body be carried to its own place, if place
was the matter or the form? It is impossible that what has no
reference to motion or the distinction of up and down can be place. So
place must be looked for among things which have these
characteristics.

    If the place is in the thing (it must be if it is either shape or
matter) place will have a place: for both the form and the
indeterminate undergo change and motion along with the thing, and
are not always in the same place, but are where the thing is. Hence
the place will have a place.

    Further, when water is produced from air, the place has been
destroyed, for the resulting body is not in the same place. What
sort of destruction then is that?

    This concludes my statement of the reasons why space must be
something, and again of the difficulties that may be raised about
its essential nature.