The Complete Aristotle (eng.)

along with itself: for the contrary is the
general view. Moreover, if it be possible for the genus stated, or
for its differentia, to be absent from the alleged species, e.g.
for ‘movement’ to be absent from the ‘soul’, or ‘truth and
falsehood’ from ‘opinion’, then neither of the terms stated could
be its genus or its differentia: for the general view is that the
genus and the differentia accompany the species, as long as it
exists.
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3
    Look and see, also, if what is placed in the genus partakes or
could possibly partake of any contrary of the genus: for in that
case the same thing will at the same time partake of contrary
things, seeing that the genus is never absent from it, while it
partakes, or can possibly partake, of the contrary genus as well.
Moreover, see whether the species shares in any character which it
is utterly impossible for any member of the genus to have. Thus
(e.g.) if the soul has a share in life, while it is impossible for
any number to live, then the soul could not be a species of
number.
    You should look and see, also, if the species be a homonym of
the genus, and employ as your elementary principles those already
stated for dealing with homonymity: for the genus and the species
are synonymous.
    Seeing that of every genus there is more than one species, look
and see if it be impossible that there should be another species
than the given one belonging to the genus stated: for if there
should be none, then clearly what has been stated could not be a
genus at all.
    Look and see, also, if he has rendered as genus a metaphorical
expression, describing (e.g. ‘temperance’ as a ‘harmony’: a
‘harmony’: for a genus is always predicated of its species in its
literal sense, whereas ‘harmony’ is predicated of temperance not in
a literal sense but metaphorically: for a harmony always consists
in notes.
    Moreover, if there be any contrary of the species, examine it.
The examination may take different forms; first of all see if the
contrary as well be found in the same genus as the species,
supposing the genus to have no contrary; for contraries ought to be
found in the same genus, if there be no contrary to the genus.
Supposing, on the other hand, that there is a contrary to the
genus, see if the contrary of the species be found in the contrary
genus: for of necessity the contrary species must be in the
contrary genus, if there be any contrary to the genus. Each of
these points is made plain by means of induction. Again, see
whether the contrary of the species be not found in any genus at
all, but be itself a genus, e.g. ‘good’: for if this be not found
in any genus, neither will its contrary be found in any genus, but
will itself be a genus, as happens in the case of ‘good’ and
‘evil’: for neither of these is found in a genus, but each of them
is a genus. Moreover, see if both genus and species be contrary to
something, and one pair of contraries have an intermediary, but not
the other. For if the genera have an intermediary, so should their
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