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addition that walking does not partake of any of the species of motion
produced by the same division except locomotion. For of necessity what
partakes of the genus partakes also of one of the species produced by
the first division of the genus. If, therefore, walking does not
partake either of increase or decrease or of the other kinds of
motion, clearly it would partake of locomotion, so that locomotion
would be the genus of walking.
Again, look among the things of which the given species is predicated
as genus, and see if what is rendered as its genus be also predicated
in the category of essence of the very things of which the species is
so predicated, and likewise if all the genera higher than this genus
are so predicated as well. For if there be anywhere a discrepancy,
clearly what has been rendered is not the true genus: for had it been
the genus, then both the genera higher than it, and it itself, would
all have been predicated in the category of essence of those objects
of which the species too is predicated in the category of essence. If,
then, you are overthrowing a view, it is useful to see whether the
genus fails to be predicated in the category of essence of those
things of which the species too is predicated. If establishing a view,
it is useful to see whether it is predicated in the category of
essence: for if so, the result will be that the genus and the species
will be predicated of the same object in the category of essence, so
that the same object falls under two genera: the genera must therefore
of necessity be subordinate one to the other, and therefore if it be
shown that the one we wish to establish as genus is not subordinate to
the species, clearly the species would be subordinate to it, so that
you may take it as shown that it is the genus.
Look, also, at the definitions of the genera, and see whether they
apply both to the given species and to the objects which partake of
the species. For of necessity the definitions of its genera must be
predicated of the species and of the objects which partake of the
species: if, then, there be anywhere a discrepancy, clearly what has
been rendered is not the genus.
Again, see if he has rendered the differentia as the genus, e.g.
'immortal' as the genus of 'God'. For 'immortal' is a differentia of
'living being', seeing that of living beings some are mortal and
others immortal. Clearly, then, a bad mistake has been made; for the
differentia of a thing is never its genus. And that this is true is
clear: for a thing's differentia never signifies its essence, but
rather some quality, as do 'walking' and 'biped'.
Also, see whether he has placed the differentia inside the genus, e.g.
by taking 'odd' as a number'. For 'odd' is a differentia of number,
not a species. Nor is the differentia generally thought to partake of
the genus: for what partakes of the genus is always either a species
or an individual, whereas the differentia is neither a species nor an
individual. Clearly, therefore, the differentia does not partake of
the genus, so that 'odd' too is no species but a differentia, seeing
that it does not partake of the genus.
Moreover, see whether he has placed the genus inside the species, e.g.
by taking 'contact' to be a 'juncture', or 'mixture' a 'fusion', or,
as in Plato's definition,' 'locomotion' to be the same as 'carriage'.
For there is no necessity that contact should be juncture: rather,
conversely, juncture must be contact: for what is in contact is not
always joined, though what is joined is always in contact. Likewise,
also, in the remaining instances: for mixture is not always a 'fusion'
(for to mix dry things does not fuse them), nor is locomotion always
'carriage'. For walking is not generally thought to be carriage: for
'carriage' is mostly used of things that change one place for another
involuntarily, as happens in the case of inanimate things. Clearly,
also, the species, in the instances given, has a wider denotation than
the genus, whereas it ought to be vice versa. Again, see whether he
has placed the differentia inside the species, by taking (e.g.)
'immortal' to be 'a god'. For the result will be that the species has
an equal or wider denotation: and this cannot be, for always the