The Complete Aristotle (eng.)

intermediates are derived from the contraries-colours, for
instance, from black and white. Everything, therefore, that comes
to be by a natural process is either a contrary or a product of
contraries.
    Up to this point we have practically had most of the other
writers on the subject with us, as I have said already: for all of
them identify their elements, and what they call their principles,
with the contraries, giving no reason indeed for the theory, but
contrained as it were by the truth itself. They differ, however,
from one another in that some assume contraries which are more
primary, others contraries which are less so: some those more
knowable in the order of explanation, others those more familiar to
sense. For some make hot and cold, or again moist and dry, the
conditions of becoming; while others make odd and even, or again
Love and Strife; and these differ from each other in the way
mentioned.
    Hence their principles are in one sense the same, in another
different; different certainly, as indeed most people think, but
the same inasmuch as they are analogous; for all are taken from the
same table of columns, some of the pairs being wider, others
narrower in extent. In this way then their theories are both the
same and different, some better, some worse; some, as I have said,
take as their contraries what is more knowable in the order of
explanation, others what is more familiar to sense. (The universal
is more knowable in the order of explanation, the particular in the
order of sense: for explanation has to do with the universal, sense
with the particular.) ‘The great and the small’, for example,
belong to the former class, ‘the dense and the rare’ to the
latter.
    It is clear then that our principles must be contraries.
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6
    The next question is whether the principles are two or three or
more in number.
    One they cannot be, for there cannot be one contrary. Nor can
they be innumerable, because, if so, Being will not be knowable:
and in any one genus there is only one contrariety, and substance
is one genus: also a finite number is sufficient, and a finite
number, such as the principles of Empedocles, is better than an
infinite multitude; for Empedocles professes to obtain from his
principles all that Anaxagoras obtains from his innumerable
principles. Lastly, some contraries are more primary than others,
and some arise from others-for example sweet and bitter, white and
black-whereas the principles must always remain principles.
    This will suffice to show that the principles are neither one
nor innumerable.
    Granted, then, that they are a limited number, it is plausible
to suppose them more than two. For it is difficult to see how
either density should be of such a nature as to act in any way on
rarity or rarity on density. The same is true of any other pair of
contraries; for Love does not gather Strife together and make
things out of it, nor does Strife make anything out of Love, but
both act on a third thing different from both. Some indeed assume
more than one such thing from which they construct the world of
nature.
    Other objections to the view that it is not necessary to assume
a third principle as a substratum may be added. (1) We do not find
that the contraries constitute the substance of any thing. But what
is a first principle ought not to be the predicate of any subject.
If it were, there would be a principle of the supposed principle:
for the subject is a principle, and prior presumably to what is
predicated of it. Again (2) we hold that a substance is not
contrary to another substance. How then can substance be derived
from what are not substances? Or how can non-substances be prior to
substance?
    If then we accept both the former argument and this one, we
must, to preserve both, assume a third somewhat as the substratum
of the contraries, such as is spoken of by those who describe the
All as one nature-water or fire or what is intermediate between
them. What is intermediate seems preferable; for fire, earth, air,
and water are 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,