The Complete Aristotle (eng.)

if it does not include the cause. E.g. what is eclipse?
Deprivation of light. But if we add ‘by the earth’s coming in
between’, this is the formula which includes the cause. In the case
of sleep it is not clear what it is that proximately has this
affection. Shall we say that it is the animal? Yes, but the animal
in virtue of what, i.e. what is the proximate subject? The heart or
some other part. Next, by what is it produced? Next, what is the
affection-that of the proximate subject, not of the whole animal?
Shall we say that it is immobility of such and such a kind? Yes,
but to what process in the proximate subject is this due?
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5
    Since some things are and are not, without coming to be and
ceasing to be, e.g. points, if they can be said to be, and in
general forms (for it is not ‘white’ comes to be, but the wood
comes to be white, if everything that comes to be comes from
something and comes to be something), not all contraries can come
from one another, but it is in different senses that a pale man
comes from a dark man, and pale comes from dark. Nor has everything
matter, but only those things which come to be and change into one
another. Those things which, without ever being in course of
changing, are or are not, have no matter.
    There is difficulty in the question how the matter of each thing
is related to its contrary states. E.g. if the body is potentially
healthy, and disease is contrary to health, is it potentially both
healthy and diseased? And is water potentially wine and vinegar? We
answer that it is the matter of one in virtue of its positive state
and its form, and of the other in virtue of the privation of its
positive state and the corruption of it contrary to its nature. It
is also hard to say why wine is not said to be the matter of
vinegar nor potentially vinegar (though vinegar is produced from
it), and why a living man is not said to be potentially dead. In
fact they are not, but the corruptions in question are accidental,
and it is the matter of the animal that is itself in virtue of its
corruption the potency and matter of a corpse, and it is water that
is the matter of vinegar. For the corpse comes from the animal, and
vinegar from wine, as night from day. And all the things which
change thus into one another must go back to their matter; e.g. if
from a corpse is produced an animal, the corpse first goes back to
its matter, and only then becomes an animal; and vinegar first goes
back to water, and only then becomes wine.
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6
    To return to the difficulty which has been stated with respect
both to definitions and to numbers, what is the cause of their
unity? In the case of all things which have several parts and in
which the totality is not, as it were, a mere heap, but the whole
is something beside the parts, there is a cause; for even in bodies
contact is the cause of unity in some cases, and in others
viscosity or some other such quality. And a definition is a set of
words which is one not by being connected together, like the Iliad,
but by dealing with one object.-What then, is it that makes man
one; why is he one and not many, e.g. animal + biped, especially if
there are, as some say, an animal-itself and a biped-itself? Why
are not those Forms themselves the man, so that men would exist by
participation not in man, nor in-one Form, but in two, animal and
biped, and in general man would be not one but more than one thing,
animal and biped?
    Clearly, then, if people proceed thus in their usual manner of
definition and speech, they cannot explain and solve the
difficulty. But if, as we say, one element is matter and another is
form, and one is potentially and the other actually, the question
will no longer be thought a difficulty. For this difficulty is the
same as would arise if ‘round bronze’ were the definition of
‘cloak’; for this word would be a sign of the definitory formula,
so that the question is, what is the cause of the unity of ‘round’
and ‘bronze’? The difficulty disappears, because the one is matter,
the other form. What, then, causes this-that which was potentially
to be actually-except, in the case of things which are generated,
the agent? For there is no other cause of the potential sphere’s
becoming actually a sphere, but this was the essence of either. Of
matter some is intelligible, some perceptible, and in a formula
there is always an element of