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all the rest. For as the species is used, so should the genus be as
well, as in the case of 'double' and its higher genera: for we say
both 'double of' and 'multiple of' a thing. Likewise, also, in the
case of 'knowledge': for both knowledge' itself and its genera, e.g.
'disposition' and 'state', are said to be 'of' something. An objection
may be raised that in some cases it is not so: for we say 'superior
to' and 'contrary to' so and so, whereas 'other', which is the genus
of these terms, demands not 'to' but 'than': for the expression is
'other than' so and so.
Again, see whether terms used in like case relationships fail to yield
a like construction when converted, as do 'double' and 'multiple'. For
each of these terms takes a genitive both in itself and in its
converted form: for we say both a half of' and 'a fraction of'
something. The case is the same also as regards both 'knowledge' and
'conception': for these take a genitive, and by conversion an 'object
of knowledge' and an 'object of conception' are both alike used with a
dative. If, then, in any cases the constructions after conversion be
not alike, clearly the one term is not the genus of the other.
Again, see whether the species and the genus fail to be used in
relation to an equal number of things: for the general view is that
the uses of both are alike and equal in number, as is the case with
'present' and 'grant'. For a present' is of something or to some one,
and also a 'grant' is of something and to some one: and 'grant' is the
genus of 'present', for a 'present' is a 'grant that need not be
returned'. In some cases, however, the number of relations in which
the terms are used happens not to be equal, for while 'double' is
double of something, we speak of 'in excess' or 'greater' in
something, as well as of or than something: for what is in excess or
greater is always in excess in something, as well as in excess of
something. Hence the terms in question are not the genera of 'double',
inasmuch as they are not used in relation to an equal number of things
with the species. Or possibly it is not universally true that species
and genus are used in relation to an equal number of things.
See, also, if the opposite of the species have the opposite of the
genus as its genus, e.g. whether, if 'multiple' be the genus of
'double', 'fraction' be also the genus of 'half'. For the opposite of
the genus should always be the genus of the opposite species. If,
then, any one were to assert that knowledge is a kind of sensation,
then also the object of knowledge will have to be a kind of object of
sensation, whereas it is not: for an object of knowledge is not always
an object of sensation: for objects of knowledge include some of the
objects of intuition as well. Hence 'object of sensation' is not the
genus of 'object of knowledge': and if this be so, neither is
'sensation' the genus of 'knowledge'.
Seeing that of relative terms some are of necessity found in, or used
of, the things in relation to which they happen at any time to be used
(e.g. 'disposition' and 'state' and 'balance'; for in nothing else can
the aforesaid terms possibly be found except in the things in relation
to which they are used), while others need not be found in the things
in relation to which they are used at any time, though they still may
be (e.g. if the term 'object of knowledge' be applied to the soul: for
it is quite possible that the knowledge of itself should be possessed
by the soul itself, but it is not necessary, for it is possible for
this same knowledge to be found in some one else), while for others,
again, it is absolutely impossible that they should be found in the
things in relation to which they happen at any time to be used (as
e.g. that the contrary should be found in the contrary or knowledge in
the object of knowledge, unless the object of knowledge happen to be a
soul or a man)-you should look, therefore, and see whether he places a
term of one kind inside a genus that is not of that kind, e.g. suppose
he has said that 'memory' is the 'abiding of knowledge'. For 'abiding'
is always found in that which abides, and is used of that, so that the
abiding of knowledge also will be found in knowledge. Memory, then, is
found in knowledge, seeing that it is the abiding of knowledge. But