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species as well, and if the species have, so should their genera as
well, as is the case with (1) virtue and vice and (2) justice and
injustice: for each pair has an intermediary. An objection to this is
that there is no intermediary between health and disease, although
there is one between evil and good. Or see whether, though there be
indeed an intermediary between both pairs, i.e. both between the
species and between the genera, yet it be not similarly related, but
in one case be a mere negation of the extremes, whereas in the other
case it is a subject. For the general view is that the relation should
be similar in both cases, as it is in the cases of virtue and vice and
of justice and injustice: for the intermediaries between both are mere
negations. Moreover, whenever the genus has no contrary, look and see
not merely whether the contrary of the species be found in the same
genus, but the intermediate as well: for the genus containing the
extremes contains the intermediates as well, as (e.g.) in the case of
white and black: for 'colour' is the genus both of these and of all
the intermediate colours as well. An objection may be raised that
'defect' and 'excess' are found in the same genus (for both are in the
genus 'evil'), whereas moderate amount', the intermediate between
them, is found not in 'evil' but in 'good'. Look and see also whether,
while the genus has a contrary, the species has none; for if the genus
be contrary to anything, so too is the species, as virtue to vice and
justice to injustice.
Likewise. also, if one were to look at other instances, one would come
to see clearly a fact like this. An objection may be raised in the
case of health and disease: for health in general is the contrary of
disease, whereas a particular disease, being a species of disease,
e.g. fever and ophthalmia and any other particular disease, has no
contrary.
If, therefore, you are demolishing a view, there are all these ways in
which you should make your examination: for if the aforesaid
characters do not belong to it, clearly what has been rendered is not
the genus. If, on the other hand, you are establishing a view, there
are three ways: in the first place, see whether the contrary of the
species be found in the genus stated, suppose the genus have no
contrary: for if the contrary be found in it, clearly the species in
question is found in it as well. Moreover, see if the intermediate
species is found in the genus stated: for whatever genus contains the
intermediate contains the extremes as well. Again, if the genus have a
contrary, look and see whether also the contrary species is found in
the contrary genus: for if so, clearly also the species in question is
found in the genus in question.
Again, consider in the case of the inflexions and the co-ordinates of
species and genus, and see whether they follow likewise, both in
demolishing and in establishing a view. For whatever attribute belongs
or does not belong to one belongs or does not belong at the same time
to all; e.g. if justice be a particular form of knowledge, then also
'justly' is 'knowingly' and the just man is a man of knowledge:
whereas if any of these things be not so, then neither is any of the
rest of them.
Part 4
Again, consider the case of things that bear a like relation to one
another. Thus (e.g.) the relation of the pleasant to pleasure is like
that of the useful to the good: for in each case the one produces the
other. If therefore pleasure be a kind of 'good', then also the
pleasant will be a kind of 'useful': for clearly it may be taken to be
productive of good, seeing that pleasure is good. In the same way also
consider the case of processes of generation and destruction; if
(e.g.) to build be to be active, then to have built is to have been
active, and if to learn be to recollect, then also to have learnt is
to have recollected, and if to be decomposed be to be destroyed, then
to have been decomposed is to have been destroyed, and decomposition
is a kind of destruction. Consider also in the same way the case of
things that generate or destroy, and of the capacities and uses of