Physics   

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.
Part 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