The Complete Aristotle (eng.)

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.
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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 in its own nature is not-being,-this not
surviving as a constituent of the result. Yet this causes surprise,
and it is thought impossible that something should come to be in
the way described from what is not.
    In the same way we maintain that nothing comes to be from being,
and that being does not come to be except in a qualified sense. In
that way, however, it does, just as animal might come to be from
animal, and an animal of a certain kind from an animal of a certain
kind. Thus, suppose a dog to come to be from a horse. The dog would
then, it is true, come to be from animal (as well as from an animal
of a certain kind) but not as animal, for that is already there.
But if anything is to become an animal, not in a qualified sense,
it will not be from animal: and if being, not from being-nor from
not-being either, for it has been explained that by ‘from not
being’ we mean from not-being qua not-being.
    Note further that we do not subvert the principle that
everything either is or is not.
    This then is one way of solving the difficulty. Another consists
in pointing out that the same things can be explained in terms of
potentiality and actuality. But this has been done with greater
precision elsewhere. So, as we said, the difficulties which
constrain people to deny the existence of some of the things we
mentioned are now solved. For it was this reason which also caused
some of the earlier thinkers to turn so far aside from the road
which leads to coming to be and passing away and change generally.
If they had come in sight of