[1019a]
[1]
because the former is an
attribute of the line in itself, and the latter of a
surface.Some things, then, are called prior and
posterior in this sense; but others (iv.) in virtue of their nature
and substance, namely all things which can exist apart from other
things, whereas other things cannot exist without them. This
distinction was used by Plato.1(And since "being" has
various meanings, (a) the substrate, and therefore substance, is
prior; (b) potential priority is different from actual
priority.Some
things are prior potentially, and some actually; e.g., potentially the
half-line is prior to the whole, or the part to the whole, or the
matter to the substance; but actually it is posterior, because it is
only upon dissolution that it will actually exist.)Indeed, in a sense all things which are
called "prior" or "posterior" are so called in this connection; for
some things can exist apart from others in generation (e.g. the whole
without the parts), and others in destruction (e.g. the parts without
the whole). And similarly with the other examples."Potency"2 means: (a) the source of motion or
change which is in something other than the thing changed, or in it
qua other. E.g., the science of building
is a potency which is not present in the thing built; but the science
of medicine, which is a potency, may be present in the patient,
although not qua patient.Thus "potency" means the source in
general of change or motion in another thing, or in the same thing qua other;
[20]
or the source of a thing's being moved or changed
by another thing, or by itself qua other (for
in virtue of that principle by which the passive thing is affected in
any way we call it capable of being affected; sometimes if it is
affected at all, and sometimes not in respect of every affection, but
only if it is changed for the better).(b) The power of performing this well or
according to intention; because sometimes we say that those who can
merely take a walk, or speak, without doing it as well as they
intended, cannot speak or walk. And similarly in the case of
passivity.(c) All
states in virtue of which things are unaffected generally, or are
unchangeable, or cannot readily deteriorate, are called "potencies."
For things are broken and worn out and bent and in general destroyed
not through potency but through impotence and deficiency of some sort;
and things are unaffected by such processes which are scarcely or
slightly affected because they have a potency and are potent and are
in a definite state.Since "potency" has all these meanings,
"potent" (or "capable") will mean (a) that which contains a source of
motion or change (for even what is static is "potent" in a sense)
which takes place in another thing, or in itself qua other.
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