The Complete Aristotle (eng.)

or man does so. (And
these too fall under the above-named causes. For the form exists
actually, if it can exist apart, and so does the complex of form
and matter, and the privation, e.g. darkness or disease; but the
matter exists potentially; for this is that which can become
qualified either by the form or by the privation.) But the
distinction of actuality and potentiality applies in another way to
cases where the matter of cause and of effect is not the same, in
some of which cases the form is not the same but different; e.g.
the cause of man is (1) the elements in man (viz. fire and earth as
matter, and the peculiar form), and further (2) something else
outside, i.e. the father, and (3) besides these the sun and its
oblique course, which are neither matter nor form nor privation of
man nor of the same species with him, but moving causes.
    Further, one must observe that some causes can be expressed in
universal terms, and some cannot. The proximate principles of all
things are the ‘this’ which is proximate in actuality, and another
which is proximate in potentiality. The universal causes, then, of
which we spoke do not exist. For it is the individual that is the
originative principle of the individuals. For while man is the
originative principle of man universally, there is no universal
man, but Peleus is the originative principle of Achilles, and your
father of you, and this particular b of this particular ba, though
b in general is the originative principle of ba taken without
qualification.
    Further, if the causes of substances are the causes of all
things, yet different things have different causes and elements, as
was said; the causes of things that are not in the same class, e.g.
of colours and sounds, of substances and quantities, are different
except in an analogical sense; and those of things in the same
species are different, not in species, but in the sense that the
causes of different individuals are different, your matter and form
and moving cause being different from mine, while in their
universal definition they are the same. And if we inquire what are
the principles or elements of substances and relations and
qualities-whether they are the same or different-clearly when the
names of the causes are used in several senses the causes of each
are the same, but when the senses are distinguished the causes are
not the same but different, except that in the following senses the
causes of all are the same. They are (1) the same or analogous in
this sense, that matter, form, privation, and the moving cause are
common to all things; and (2) the causes of substances may be
treated as causes of all things in this sense, that when substances
are removed all things are removed; further, (3) that which is
first in respect of complete reality is the cause of all things.
But in another sense there are different first causes, viz. all the
contraries which are neither generic nor ambiguous terms; and,
further, the matters of different things are different. We have
stated, then, what are the principles of sensible things and how
many they are, and in what sense they are the same and in what
sense different.
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6
    Since there were three kinds of substance, two of them physical
and one unmovable, regarding the latter we must assert that it is
necessary that there should be an eternal unmovable substance. For
substances are the first of existing things, and if they are all
destructible, all things are destructible. But it is impossible
that movement should either have come into being or cease to be
(for it must always have existed), or that time should. For there
could not be a before and an after if time did not exist. Movement
also is continuous, then, in the sense in which time is; for time
is either the same thing as movement or an attribute of movement.
And there is no continuous movement except movement in place, and
of this only that which is circular is continuous.
    But if there is something which is capable of moving things or
acting on them, but is not actually doing so, there will not
necessarily be movement; for that which has a potency need not
exercise it. Nothing, then, is gained even if we suppose eternal
substances, as the believers in the Forms do, unless there is to be
in them some principle which can cause change; nay, even this is
not enough, nor is another substance besides the Forms enough; for
if it is not to act, there will be no movement.