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motion, so that, if rest is the better of the two, this is the genus
into which the soul should have been put.
Moreover, judge by means of greater and less degrees: if overthrowing
a view, see whether the genus admits of a greater degree, whereas
neither the species itself does so, nor any term that is called after
it: e.g. if virtue admits of a greater degree, so too does justice and
the just man: for one man is called 'more just than another'. If,
therefore, the genus rendered admits of a greater degree, whereas
neither the species does so itself nor yet any term called after it,
then what has been rendered could not be the genus.
Again, if what is more generally, or as generally, thought to be the
genus be not so, clearly neither is the genus rendered. The
commonplace rule in question is useful especially in cases where the
species appears to have several predicates in the category of essence,
and where no distinction has been drawn between them, and we cannot
say which of them is genus; e.g. both 'pain' and the 'conception of a
slight' are usually thought to be predicates of 'anger in the category
of essence: for the angry man is both in pain and also conceives that
he is slighted. The same mode of inquiry may be applied also to the
case of the species, by comparing it with some other species: for if
the one which is more generally, or as generally, thought to be found
in the genus rendered be not found therein, then clearly neither could
the species rendered be found therein.
In demolishing a view, therefore, you should follow the rule as
stated. In establishing one, on the other hand, the commonplace rule
that you should see if both the genus rendered and the species admit
of a greater degree will not serve: for even though both admit it, it
is still possible for one not to be the genus of the other. For both
'beautiful' and 'white' admit of a greater degree, and neither is the
genus of the other. On the other hand, the comparison of the genera
and of the species one with another is of use: e.g. supposing A and B
to have a like claim to be genus, then if one be a genus, so also is
the other. Likewise, also, if what has less claim be a genus, so also
is what has more claim: e.g. if 'capacity' have more claim than
'virtue' to be the genus of self-control, and virtue be the genus, so
also is capacity. The same observations will apply also in the case of
the species. For instance, supposing A and B to have a like claim to
be a species of the genus in question, then if the one be a species,
so also is the other: and if that which is less generally thought to
be so be a species, so also is that which is more generally thought to
be so.
Moreover, to establish a view, you should look and see if the genus is
predicated in the category of essence of those things of which it has
been rendered as the genus, supposing the species rendered to be not
one single species but several different ones: for then clearly it
will be the genus. If, on the other, the species rendered be single,
look and see whether the genus be predicated in the category of
essence of other species as well: for then, again, the result will be
that it is predicated of several different species.
Since some people think that the differentia, too, is a predicate of
the various species in the category of essence, you should distinguish
the genus from the differentia by employing the aforesaid elementary
principles-(a) that the genus has a wider denotation than the
differentia; (b) that in rendering the essence of a thing it is more
fitting to state the genus than the differentia: for any one who says
that 'man' is an 'animal' shows what man is better than he who
describes him as 'walking'; also (c) that the differentia always
signifies a quality of the genus, whereas the genus does not do this
of the differentia: for he who says 'walking' describes an animal of a
certain quality, whereas he who says 'animal' describes an animal of a
certain quality, whereas he who says 'animal' does not describe a
walking thing of a certain quality.
The differentia, then, should be distinguished from the genus in this
manner. Now seeing it is generally held that if what is musical, in