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another life, but that a certain accidental feature or affection
enters into this one as it is. So then 'life' is not the genus of
immortality.
Again, see if to an affection he has ascribed as genus the object of
which it is an affection, by defining (e.g.) wind as 'air in motion'.
Rather, wind is 'a movement of air': for the same air persists both
when it is in motion and when it is still. Hence wind is not 'air' at
all: for then there would also have been wind when the air was not in
motion, seeing that the same air which formed the wind persists.
Likewise, also, in other cases of the kind. Even, then, if we ought in
this instance to admit the point that wind is 'air in motion', yet we
should accept a definition of the kind, not about all those things of
which the genus is not true, but only in cases where the genus
rendered is a true predicate. For in some cases, e.g. 'mud' or 'snow',
it is not generally held to be true. For people tell you that snow is
'frozen water' and mud is earth mixed with moisture', whereas snow is
not water, nor mud earth, so that neither of the terms rendered could
be the genus: for the genus should be true of all its species.
Likewise neither is wine 'fermented water', as Empedocles speaks of
'water fermented in wood';' for it simply is not water at all.
Part 6
Moreover, see whether the term rendered fail to be the genus of
anything at all; for then clearly it also fails to be the genus of the
species mentioned. Examine the point by seeing whether the objects
that partake of the genus fail to be specifically different from one
another, e.g. white objects: for these do not differ specifically from
one another, whereas of a genus the species are always different, so
that 'white' could not be the genus of anything.
Again, see whether he has named as genus or differentia some feature
that goes with everything: for the number of attributes that follow
everything is comparatively large: thus (e.g.) 'Being' and 'Unity' are
among the number of attributes that follow everything. If, therefore,
he has rendered 'Being' as a genus, clearly it would be the genus of
everything, seeing that it is predicated of everything; for the genus
is never predicated of anything except of its species. Hence Unity,
inter alia, will be a species of Being. The result, therefore, is that
of all things of which the genus is predicated, the species is
predicated as well, seeing that Being and Unity are predicates of
absolutely everything, whereas the predication of the species ought to
be of narrower range. If, on the other hand, he has named as
differentia some attribute that follows everything, clearly the
denotation of the differentia will be equal to, or wider than, that of
the genus. For if the genus, too, be some attribute that follows
everything, the denotation of the differentia will be equal to its
denotation, while if the genus do not follow everything, it will be
still wider.
Moreover, see if the description 'inherent in S' be used of the genus
rendered in relation to its species, as it is used of 'white' in the
case of snow, thus showing clearly that it could not be the genus: for
'true of S' is the only description used of the genus in relation to
its species. Look and see also if the genus fails to be synonymous
with its species. For the genus is always predicated of its species
synonymously.
Moreover, beware, whenever both species and genus have a contrary, and
he places the better of the contraries inside the worse genus: for the
result will be that the remaining species will be found in the
remaining genus, seeing that contraries are found in contrary genera,
so that the better species will be found in the worse genus and the
worse in the better: whereas the usual view is that of the better
species the genus too is better. Also see if he has placed the species
inside the worse and not inside the better genus, when it is at the
same time related in like manner to both, as (e.g.) if he has defined
the 'soul' as a 'form of motion' or 'a form of moving thing'. For the
same soul is usually thought to be a principle alike of rest and of