Next in order we must discuss 'action' and 'passion'. The
traditional theories on the subject are conflicting. For (i) most
thinkers are unanimous in maintaining (a) that 'like' is always
unaffected by 'like', because (as they argue) neither of two 'likes'
is more apt than the other either to act or to suffer action, since
all the properties which belong to the one belong identically and in
the same degree to the other; and (b) that 'unlikes', i.e.
'differents', are by nature such as to act and suffer action
reciprocally. For even when the smaller fire is destroyed by the
greater, it suffers this effect (they say) owing to its
'contrariety' since the great is contrary to the small. But (ii)
Democritus dissented from all the other thinkers and maintained a
theory peculiar to himself. He asserts that agent and patient are
identical, i.e. 'like'. It is not possible (he says) that 'others',
i.e. 'differents', should suffer action from one another: on the
contrary, even if two things, being 'others', do act in some way on
one another, this happens to them not qua 'others' but qua
possessing an identical property.
Such, then, are the traditional theories, and it looks as if the
statements of their advocates were in manifest conflict. But the
reason of this conflict is that each group is in fact stating a
part, whereas they ought to have taken a comprehensive view of the
subject as a whole. For (i) if A and B are 'like'-absolutely and in
all respects without difference from one another -it is reasonable
to infer that neither is in any way affected by the other. Why,
indeed, should either of them tend to act any more than the other?
Moreover, if 'like' can be affected by 'like', a thing can also be
affected by itself: and yet if that were so-if 'like' tended in fact
to act qua 'like'-there would be nothing indestructible or
immovable, for everything would move itself. And (ii) the same
consequence follows if A and B are absolutely 'other', i.e. in no
respect identical. Whiteness could not be affected in any way by
line nor line by whiteness-except perhaps 'coincidentally', viz. if
the line happened to be white or black: for unless two things either
are, or are composed of, 'contraries', neither drives the other out of
its natural condition. But (iii) since only those things which
either involve a 'contrariety' or are 'contraries'-and not any
things selected at random-are such as to suffer action and to act,
agent and patient must be 'like' (i.e. identical) in kind and yet
'unlike' (i.e. contrary) in species. (For it is a law of nature that
body is affected by body, flavour by flavour, colour by colour, and so
in general what belongs to any kind by a member of the same kind-the
reason being that 'contraries' are in every case within a single
identical kind, and it is 'contraries' which reciprocally act and
suffer action.) Hence agent and patient must be in one sense
identical, but in another sense other than (i.e. 'unlike') one
another. And since (a) patient and agent are generically identical
(i.e. 'like') but specifically 'unlike', while (b) it is
'contraries' that exhibit this character: it is clear that
'contraries' and their 'intermediates' are such as to suffer action
and to act reciprocally-for indeed it is these that constitute the
entire sphere of passing-away and coming-to-be.
We can now understand why fire heats and the cold thing cools, and
in general why the active thing assimilates to itself the patient. For
agent and patient are contrary to one another, and coming-to-be is a
process into the contrary: hence the patient must change into the
agent, since it is only thus that coming-to be will be a process
into the contrary. And, again, it is intelligible that the advocates
of both views, although their theories are not the same, are yet in
contact with the nature of the facts. For sometimes we speak of the
substratum as suffering action (e.g. of 'the man' as being healed,
being warmed and chilled, and similarly in all the other cases), but
at other times we say 'what is cold is 'being warmed', 'what is sick
is being healed': and in both these ways of speaking we express the
truth, since in one sense it is the 'matter', while in another sense
it is the 'contrary', which suffers action. (We make the same
distinction in speaking of the agent: for sometimes we say that 'the
man', but at other times that 'what is hot', produces heat.) Now the
one group of thinkers supposed that agent and patient must possess
something identical, because they fastened their attention on the
substratum: while the other group maintained the opposite because
their attention was concentrated on the 'contraries'. We must conceive
the same account to hold of action and passion as that which is true
of 'being moved' and 'imparting motion'. For the 'mover', like the
'agent', has two meanings. Both (a) that which contains the
originative source of the motion is thought to 'impart motion' (for
the originative source is first amongst the causes), and also (b) that
which is last, i.e. immediately next to the moved thing and to the
coming-to-be. A similar distinction holds also of the agent: for we
speak not only (a) of the doctor, but also (b) of the wine, as
healing. Now, in motion, there is nothing to prevent the first; mover
being unmoved (indeed, as regards some 'first' movers' this is
actually necessary) although the last mover always imparts motion by
being itself moved: and, in action, there is nothing to prevent the
first agent being unaffected, while the last agent only acts by
suffering action itself. For agent and patient have not the same
matter, agent acts without being affected: thus the art of healing
produces health without itself being acted upon in any way by that
which is being healed. But (b) the food, in acting, is itself in
some way acted upon: for, in acting, it is simultaneously heated or
cooled or otherwise affected. Now the art of healing corresponds to an
'originative source', while the food corresponds to 'the last' (i.e.
'continuous') mover.
Those active powers, then, whose forms are not embodied in matter,
are unaffected: but those whose forms are in matter are such as to
be affected in acting. For we maintain that one and the same
'matter' is equally, so to say, the basis of either of the two opposed
things-being as it were a 'kind'; and that that which can he hot
must be made hot, provided the heating agent is there, i.e. comes
near. Hence (as we have said) some of the active powers are unaffected
while others are such as to be affected; and what holds of motion is
true also of the active powers. For as in motion 'the first mover'
is unmoved, so among the active powers 'the first agent' is
unaffected.
The active power is a 'cause' in the sense of that from which the
process originates: but the end, for the sake of which it takes place,
is not 'active'. (That is why health is not 'active', except
metaphorically.) For when the agent is there, the patient he-comes
something: but when 'states' are there, the patient no longer
becomes but already is-and 'forms' (i.e. lends') are a kind of
'state'. As to the 'matter', it (qua matter) is passive. Now fire
contains 'the hot' embodied in matter: but a 'hot' separate from
matter (if such a thing existed) could not suffer any action. Perhaps,
indeed, it is impossible that 'the hot' should exist in separation
from matter: but if there are any entities thus separable, what we are
saying would be true of them.
We have thus explained what action and passion are, what things
exhibit them, why they do so, and in what manner. We must go on to
discuss how it is possible for action and passion to take place.