Physics   

already involved with pairs of contraries. There is, therefore, much
to be said for those who make the underlying substance different from
these four; of the rest, the next best choice is air, as presenting
sensible differences in a less degree than the others; and after air,
water. All, however, agree in this, that they differentiate their One
by means of the contraries, such as density and rarity and more and
less, which may of course be generalized, as has already been said
into excess and defect. Indeed this doctrine too (that the One and
excess and defect are the principles of things) would appear to be of
old standing, though in different forms; for the early thinkers made
the two the active and the one the passive principle, whereas some of
the more recent maintain the reverse.
To suppose then that the elements are three in number would seem, from
these and similar considerations, a plausible view, as I said before.
On the other hand, the view that they are more than three in number
would seem to be untenable.
For the one substratum is sufficient to be acted on; but if we have
four contraries, there will be two contrarieties, and we shall have to
suppose an intermediate nature for each pair separately. If, on the
other hand, the contrarieties, being two, can generate from each
other, the second contrariety will be superfluous. Moreover, it is
impossible that there should be more than one primary contrariety. For
substance is a single genus of being, so that the principles can
differ only as prior and posterior, not in genus; in a single genus
there is always a single contrariety, all the other contrarieties in
it being held to be reducible to one.
It is clear then that the number of elements is neither one nor more
than two or three; but whether two or three is, as I said, a question
of considerable difficulty.
Part 7
We will now give our own account, approaching the question first with
reference to becoming in its widest sense: for we shall be following
the natural order of inquiry if we speak first of common
characteristics, and then investigate the characteristics of special
cases.
We say that one thing comes to be from another thing, and one sort of
thing from another sort of thing, both in the case of simple and of
complex things. I mean the following. We can say (1) 'man becomes
musical', (2) what is 'not-musical becomes musical', or (3), the
'not-musical man becomes a musical man'. Now what becomes in (1) and
(2)-'man' and 'not musical'-I call simple, and what each
becomes-'musical'-simple also. But when (3) we say the 'not-musical
man becomes a musical man', both what becomes and what it becomes are
complex.
As regards one of these simple 'things that become' we say not only
'this becomes so-and-so', but also 'from being this, comes to be
so-and-so', as 'from being not-musical comes to be musical'; as
regards the other we do not say this in all cases, as we do not say
(1) 'from being a man he came to be musical' but only 'the man became
musical'.
When a 'simple' thing is said to become something, in one case (1) it
survives through the process, in the other (2) it does not. For man
remains a man and is such even when he becomes musical, whereas what
is not musical or is unmusical does not continue to exist, either
simply or combined with the subject.
These distinctions drawn, one can gather from surveying the various
cases of becoming in the way we are describing that, as we say, there
must always be an underlying something, namely that which becomes, and
that this, though always one numerically, in form at least is not one.
(By that I mean that it can be described in different ways.) For 'to
be man' is not the same as 'to be unmusical'. One part survives, the
other does not: what is not an opposite survives (for 'man' survives),
but 'not-musical' or 'unmusical' does not survive, nor does the
compound of the two, namely 'unmusical man'.