Physics   

man' is different from 'to be unmusical', and 'to be unformed' from
'to be bronze'.
We have now stated the number of the principles of natural objects
which are subject to generation, and how the number is reached: and it
is clear that there must be a substratum for the contraries, and that
the contraries must be two. (Yet in another way of putting it this is
not necessary, as one of the contraries will serve to effect the
change by its successive absence and presence.)
The underlying nature is an object of scientific knowledge, by an
analogy. For as the bronze is to the statue, the wood to the bed, or
the matter and the formless before receiving form to any thing which
has form, so is the underlying nature to substance, i.e. the 'this' or
existent.
This then is one principle (though not one or existent in the same
sense as the 'this'), and the definition was one as we agreed; then
further there is its contrary, the privation. In what sense these are
two, and in what sense more, has been stated above. Briefly, we
explained first that only the contraries were principles, and later
that a substratum was indispensable, and that the principles were
three; our last statement has elucidated the difference between the
contraries, the mutual relation of the principles, and the nature of
the substratum. Whether the form or the substratum is the essential
nature of a physical object is not yet clear. But that the principles
are three, and in what sense, and the way in which each is a
principle, is clear.
So much then for the question of the number and the nature of the
principles.
Part 8
We will now proceed to show that the difficulty of the early thinkers,
as well as our own, is solved in this way alone.
The first of those who studied science were misled in their search for
truth and the nature of things by their inexperience, which as it were
thrust them into another path. So they say that none of the things
that are either comes to be or passes out of existence, because what
comes to be must do so either from what is or from what is not, both
of which are impossible. For what is cannot come to be (because it is
already), and from what is not nothing could have come to be (because
something must be present as a substratum). So too they exaggerated
the consequence of this, and went so far as to deny even the existence
of a plurality of things, maintaining that only Being itself is. Such
then was their opinion, and such the reason for its adoption.
Our explanation on the other hand is that the phrases 'something comes
to be from what is or from what is not', 'what is not or what is does
something or has something done to it or becomes some particular
thing', are to be taken (in the first way of putting our explanation)
in the same sense as 'a doctor does something or has something done to
him', 'is or becomes something from being a doctor.' These expressions
may be taken in two senses, and so too, clearly, may 'from being', and
'being acts or is acted on'. A doctor builds a house, not qua doctor,
but qua housebuilder, and turns gray, not qua doctor, but qua
dark-haired. On the other hand he doctors or fails to doctor qua
doctor. But we are using words most appropriately when we say that a
doctor does something or undergoes something, or becomes something
from being a doctor, if he does, undergoes, or becomes qua doctor.
Clearly then also 'to come to be so-and-so from not-being' means 'qua
not-being'.
It was through failure to make this distinction that those thinkers
gave the matter up, and through this error that they went so much
farther astray as to suppose that nothing else comes to be or exists
apart from Being itself, thus doing away with all becoming.
We ourselves are in agreement with them in holding that nothing can be
said without qualification to come from what is not. But nevertheless
we maintain that a thing may 'come to be from what is not'-that is, in
a qualified sense. For a thing comes to be from the privation, which