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Pages of Metaphysics

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privation is in a sense 'having' or 'habit', everything will be
capable by having something, so that things are capable both by having
a positive habit and principle, and by having the privation of this,
if it is possible to have a privation; and if privation is not in a
sense 'habit', 'capable' is used in two distinct senses); and a
thing is capable in another sense because neither any other thing, nor
itself qua other, has a potency or principle which can destroy it.
Again, all of these are capable either merely because the thing
might chance to happen or not to happen, or because it might do so
well. This sort of potency is found even in lifeless things, e.g. in
instruments; for we say one lyre can speak, and another cannot speak
at all, if it has not a good tone.
Incapacity is privation of capacity-i.e. of such a principle as
has been described either in general or in the case of something
that would naturally have the capacity, or even at the time when it
would naturally already have it; for the senses in which we should
call a boy and a man and a eunuch 'incapable of begetting' are
distinct.-Again, to either kind of capacity there is an opposite
incapacity-both to that which only can produce movement and to that
which can produce it well.
Some things, then, are called adunata in virtue of this kind of
incapacity, while others are so in another sense; i.e. both dunaton
and adunaton are used as follows. The impossible is that of which
the contrary is of necessity true, e.g. that the diagonal of a
square is commensurate with the side is impossible, because such a
statement is a falsity of which the contrary is not only true but also
necessary; that it is commensurate, then, is not only false but also
of necessity false. The contrary of this, the possible, is found
when it is not necessary that the contrary is false, e.g. that a man
should be seated is possible; for that he is not seated is not of
necessity false. The possible, then, in one sense, as has been said,
means that which is not of necessity false; in one, that which is
true; in one, that which may be true.-A 'potency' or 'power' in
geometry is so called by a change of meaning.-These senses of
'capable' or 'possible' involve no reference to potency. But the
senses which involve a reference to potency all refer to the primary
kind of potency; and this is a source of change in another thing or in
the same thing qua other. For other things are called 'capable',
some because something else has such a potency over them, some because
it has not, some because it has it in a particular way. The same is
true of the things that are incapable. Therefore the proper definition
of the primary kind of potency will be 'a source of change in
another thing or in the same thing qua other'.

'Quantum' means that which is divisible into two or more
constituent parts of which each is by nature a 'one' and a 'this'. A
quantum is a plurality if it is numerable, a magnitude if it is a
measurable. 'Plurality' means that which is divisible potentially into
non-continuous parts, 'magnitude' that which is divisible into
continuous parts; of magnitude, that which is continuous in one
dimension is length; in two breadth, in three depth. Of these, limited
plurality is number, limited length is a line, breadth a surface,
depth a solid.
Again, some things are called quanta in virtue of their own
nature, others incidentally; e.g. the line is a quantum by its own
nature, the musical is one incidentally. Of the things that are quanta
by their own nature some are so as substances, e.g. the line is a
quantum (for 'a certain kind of quantum' is present in the
definition which states what it is), and others are modifications
and states of this kind of substance, e.g. much and little, long and
short, broad and narrow, deep and shallow, heavy and light, and all
other such attributes. And also great and small, and greater and
smaller, both in themselves and when taken relatively to each other,

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