by Aristotle
there are three ways: in the first place, see whether the contrary
of the species be found in the genus stated, suppose the genus have no
contrary: for if the contrary be found in it, clearly the species in
question is found in it as well. Moreover, see if the intermediate
species is found in the genus stated: for whatever genus contains
the intermediate contains the extremes as well. Again, if the genus
have a contrary, look and see whether also the contrary species is
found in the contrary genus: for if so, clearly also the species in
question is found in the genus in question.
Again, consider in the case of the inflexions and the co-ordinates
of species and genus, and see whether they follow likewise, both in
demolishing and in establishing a view. For whatever attribute belongs
or does not belong to one belongs or does not belong at the same
time to all; e.g. if justice be a particular form of knowledge, then
also 'justly' is 'knowingly' and the just man is a man of knowledge:
whereas if any of these things be not so, then neither is any of the
rest of them.
4
Again, consider the case of things that bear a like relation to
one another. Thus (e.g.) the relation of the pleasant to pleasure is
like that of the useful to the good: for in each case the one produces
the other. If therefore pleasure be a kind of 'good', then also the
pleasant will be a kind of 'useful': for clearly it may be taken to be
productive of good, seeing that pleasure is good. In the same way also
consider the case of processes of generation and destruction; if
(e.g.) to build be to be active, then to have built is to have been
active, and if to learn be to recollect, then also to have learnt is
to have recollected, and if to be decomposed be to be destroyed,
then to have been decomposed is to have been destroyed, and
decomposition is a kind of destruction. Consider also in the same
way the case of things that generate or destroy, and of the capacities
and uses of things; and in general, both in demolishing and in
establishing an argument, you should examine things in the light of
any resemblance of whatever description, as we were saying in the case
of generation and destruction. For if what tends to destroy tends to
decompose, then also to be destroyed is to be decomposed: and if
what tends to generate tends to produce, then to be generated is to be
produced, and generation is production. Likewise, also, in the case of
the capacities and uses of things: for if a capacity be a disposition,
then also to be capable of something is to be disposed to it, and if
the use of anything be an activity, then to use it is to be active,
and to have used it is to have been active.
If the opposite of the species be a privation, there are two ways of
demolishing an argument, first of all by looking to see if the
opposite be found in the genus rendered: for either the privation is
to be found absolutely nowhere in the same genus, or at least not in
the same ultimate genus: e.g. if the ultimate genus containing sight
be sensation, then blindness will not be a sensation. Secondly, if
there be a sensation. Secondly, if there be a privation opposed to
both genus and species, but the opposite of the species be not found
in the opposite of the genus, then neither could the species
rendered be in the genus rendered. If, then, you are demolishing a
view, you should follow the rule as stated; but if establishing one
there is but one way: for if the opposite species be found in the
opposite genus, then also the species in question would be found in
the genus in question: e.g. if 'blindness' be a form of
'insensibility', then 'sight' is a form of 'sensation'.
Again, look at the negations of the genus and species and convert
the order of terms, according to the method described in the case of
Accident: e.g. if the pleasant be a kind of good, what is not good
is not pleasant. For were this no something not good as well would
then be pleasant. That, however, cannot be, for it is impossible, if
'good' be the genus of pleasant, that anything not good should be
pleasant: for of things of which the genus is not predicated, none
of the species is predicated either. Also, in establishing a view, you
should adopt the same method of examination: for if what is not good
be not pleasant, then what is pleasant is good, so that 'good' is
the genus of 'pleasant'.
If the species be a relative term, see whether the genus be a
relative term as well: for if the species be a relative term, so too
is the genus, as is the case with 'double' and 'multiple': for each is
a relative term. If, on the other hand, the genus be a relative
term, there is no necessity that the species should be so as well: for
'knowledge'is a relative term, but not so 'grammar'. Or possibly not
even the first statement would be generally considered true: for
virtue is a kind of 'noble' and a kind of 'good' thing, and yet, while
'virtue' is a relative term, 'good' and 'noble' are not relatives
but qualities. Again, see whether the species fails to be used in
the same relation when called by its own name, and when called by
the name of its genus: e.g. if the term 'double' be used to mean the
double of a 'half', then also the term 'multiple' ought to be used
to mean multiple of a 'half'. Otherwise 'multiple' could not be the
genus of 'double'.
Moreover, see whether the term fail to be used in the same
relation both when called by the name of its genus, and also when
called by those of all the genera of its genus. For if the double be a
multiple of a half, then 'in excess of 'will also be used in
relation to a 'half': and, in general, the double will be called by
the names of all the higher genera in relation to a 'half'. An
objection may be raised that there is no necessity for a term to be
used in the same relation when called by its own name and when
called by that of its genus: for 'knowledge' is called knowledge 'of
an object', whereas it is called a 'state' and 'disposition' not of an
'object' but of the 'soul'.
Again, see whether the genus and the species be used in the same way
in respect of the inflexions they take, e.g. datives and genitives and
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 converte
d 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 this is
impossible, for memory is always found in the soul. The aforesaid
commonplace rule is common to the subject of Accident as well: for
it is all the same to say that 'abiding' is the genus of memory, or to
allege that it is an accident of it. For if in any way whatever memory
be the abiding of knowledge, the same argument in regard to it will
apply.
5
Again, see if he has placed what is a 'state' inside the genus
'activity', or an activity inside the genus 'state', e.g. by
defining 'sensation' as 'movement communicated through the body':
for sensation is a 'state', whereas movement is an 'activity'.
Likewise, also, if he has said that memory is a 'state that is
retentive of a conception', for memory is never a state, but rather an
activity.
They also make a bad mistake who rank a 'state' within the
'capacity' that attends it, e.g. by defining 'good temper' as the
'control of anger', and 'courage' and 'justice' as 'control of
fears' and of 'gains': for the terms 'courageous' and
'good-tempered' are applied to a man who is immune from passion,
whereas 'self-controlled' describes the man who is exposed to
passion and not led by it. Quite possibly, indeed, each of the
former is attended by a capacity such that, if he were exposed to
passion, he would control it and not be led by it: but, for all
that, this is not what is meant by being 'courageous' in the one case,
and 'good tempered' in the other; what is meant is an absolute
immunity from any passions of that kind at all.
Sometimes, also, people state any kind of attendant feature as the
genus, e.g. 'pain' as the genus of 'anger' and 'conception' as that of
conviction'. For both of the things in question follow in a certain
sense upon the given species, but neither of them is genus to it.
For when the angry man feels pain, the pain bas appeared in him
earlier than the anger: for his anger is not the cause of his pain,
but his pain of his anger, so that anger emphatically is not pain.
By the same reasoning, neither is conviction conception: for it is
possible to have the same conception even without being convinced of
it, whereas this is impossible if conviction be a species of
conception: for it is impossible for a thing still to remain the
same if it be entirely transferred out of its species, just as neither
could the same animal at one time be, and at another not be, a man.
If, on the other hand, any one says that a man who has a conception
must of necessity be also convinced of it, then 'conception' and
'conviction' will be used with an equal denotation, so that not even
so could the former be the genus of the latter: for the denotation
of the genus should be wider.
See, also, whether both naturally come to be anywhere in the same
thing: for what contains the species contains the genus as well:
e.g. what contains 'white' contains 'colour' as well, and what
contains 'knowledge of grammar' contains 'knowledge' as well. If,
therefore, any one says that 'shame' is 'fear', or that 'anger' is
'pain', the result will be that genus and species are not found in the
same thing: for shame is found in the 'reasoning' faculty, whereas
fear is in the 'spirited' faculty, and 'pain' is found in the
faculty of 'desires'. (for in this pleasure also is found), whereas
'anger' is found in the 'spirited' faculty. Hence the terms rendered
are not the genera, seeing that they do not naturally come to be in
the
same faculty as the species. Likewise, also, if 'friendship' be
found in the faculty of desires, you may take it that it is not a form
of 'wishing': for wishing is always found in the 'reasoning'
faculty. This commonplace rule is useful also in dealing with
Accident: for the accident and that of which it is an accident are
both found in the same thing, so that if they do not appear in the
same thing, clearly it is not an accident.
Again, see if the species partakes of the genus attributed only in
some particular respect: for it is the general view that the genus
is not thus imparted only in some particular respect: for a man is not
an animal in a particular respect, nor is grammar knowledge in a
particular respect only. Likewise also in other instances. Look,
therefore, and see if in the case of any of its species the genus be
imparted only in a certain respect; e.g. if 'animal' has been
described as an 'object of perception' or of 'sight'. For an animal is
an object of perception or of sight in a particular respect only;
for it is in respect of its body that it is perceived and seen, not in
respect of its soul, so that-'object of sight' and 'object of
perception' could not be the genus of 'animal'.
Sometimes also people place the whole inside the part without
detection, defining (e.g.) 'animal' as an 'animate body'; whereas
the part is not predicated in any sense of the whole, so that 'body'
could not be the genus of animal, seeing that it is a part.
See also if he has put anything that is blameworthy or objectionable
into the class 'capacity' or 'capable', e.g. by defining a 'sophist'
or a 'slanderer', or a 'thief' as 'one who is capable of secretly
thieving other people's property'. For none of the aforesaid
characters is so called because he is 'capable' in one of these
respects: for even God and the good man are capable of doing bad
things, but that is not their character: for it is always in respect
of their choice that bad men are so called. Moreover, a capacity is
always a desirable thing: for even the capacities for doing bad things