by Aristotle
either, since what partakes of the genus must necessarily partake of
one of the species as well: so that pleasure could not be a species of
Motion, nor yet be one of the individual phenomena comprised under the
term 'motion'. For individuals as well partake in the genus and the
species, as (e.g.) an individual man partakes of both 'man' and
'animal'.
Moreover, see if the term placed in the genus has a wider denotation
than the genus, as (e.g.) 'object of opinion' has, as compared with
'being': for both what is and what is not are objects of opinion, so
that 'object of opinion' could not be a species of being: for the
genus is always of wider denotation than the species. Again, see if
the species and its genus have an equal denotation; suppose, for
instance, that of the attributes which go with everything, one were to
be stated as a species and the other as its genus, as for example
Being and Unity: for everything has being and unity, so that neither
is the genus of the other, since their denotation is equal.
Likewise, also, if the 'first' of a series and the 'beginning' were to
be placed one under the other: for the beginning is first and the
first is the beginning, so that either both expressions are
identical or at any rate neither is the genus of the other. The
elementary principle in regard to all such cases is that the genus has
a wider denotation than the species and its differentia: for the
differentia as well has a narrower denotation than the genus.
See also whether the genus mentioned fails, or might be generally
thought to fail, to apply to some object which is not specifically
different from the thing in question; or, if your argument be
constructive, whether it does so apply. For all things that are not
specifically different have the same genus. If, therefore, it be shown
to apply to one, then clearly it applies to all, and if it fails to
apply to one, clearly it fails to apply to any; e.g. if any one who
assumes 'indivisible lines' were to say that the 'indivisible' is
their genus. For the aforesaid term is not the genus of divisible
lines, and these do not differ as regards their species from
indivisible: for straight lines are never different from each other as
regards their species.
2
Look and see, also, if there be any other genus of the given species
which neither embraces the genus rendered nor yet falls under it, e.g.
suppose any one were to lay down that 'knowledge' is the genus of
justice. For virtue is its genus as well, and neither of these
genera embraces the remaining one, so that knowledge could not be
the genus of justice: for it is generally accepted that whenever one
species falls under two genera, the one is embraced by the other.
Yet a principle of this kind gives rise to a difficulty in some cases.
For some people hold that prudence is both virtue and knowledge, and
that neither of its genera is embraced by the other: although
certainly not everybody admits that prudence is knowledge. If,
however, any one were to admit the truth of this assertion, yet it
would still be generally agreed to be necessary that the genera of the
same object must at any rate be subordinate either the one to the
other or both to the same, as actually is the case with virtue and
knowledge. For both fall under the same genus; for each of them is a
state and a disposition. You should look, therefore, and see whether
neither of these things is true of the genus rendered; for if the
genera be subordinate neither the one to the other nor both to the
same, then what is rendered could not be the true genus.
Look, also, at the genus of the genus rendered, and so continually
at the next higher genus, and see whether all are predicated of the
species, and predicated in the category of essence: for all the higher
genera should be predicated of the species in the category of essence.
If, then, there be anywhere a discrepancy, clearly what is rendered is
not the true genus. [Again, see whether either the genus itself, or
one of its higher genera, partakes of the species: for the higher
genus does not partake of any of the lower.] If, then, you are
overthrowing a view, follow the rule as given: if establishing one,
then-suppose that what has been named as genus be admitted to belong
to the species, only it be disputed whether it belongs as genus-it
is enough to show that one of its higher genera is predicated of the
species in the category of essence. For if one of them be predicated
in the category of essence, all of them, both higher and lower than
this one, if predicated at all of the species, will be predicated of
it in the category of essence: so that what has been rendered as genus
is also predicated in the category of essence. The premiss that when
one genus is predicated in the category of essence, all the rest, if
predicated at all, will be predicated in the category of essence,
should be secured by induction. Supposing, however, that it be
disputed whether what has been rendered as genus belongs at all, it is
not enough to show that one of the higher genera is predicated of
the species in the category of essence: e.g. if any one has rendered
'locomotion' as the genus of walking, it is not enough to show that
walking is 'motion' in order to show that it is 'locomotion', seeing
that there are other forms of motion as well; but one must show in
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 th
at 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 differentia has an equal or a wider
denotation than the species. Moreover, see whether he has placed the
genus inside the differentia, by making 'colour' (e.g.) to be a
thing that 'pierces', or 'number' a thing that is 'odd'. Also, see
if he has mentioned the genus as differentia: for it is possible for a
man to bring forward a statement of this kind as well, e.g. that
'mixture' is the differentia of 'fusion', or that change of place'
is the differentia of 'carriage'. All such cases should be examined by
means of the same principles: for they depend upon common rules: for
the genus should have a wider denotation that its differentia, and
also should not partake of its differentia; whereas, if it be rendered
in this manner, neither of the aforesaid requirements can be
satisfied: for the genus will both have a narrower denotation than its
differentia, and will partake of it.
Again, if no differentia belonging to the genus be predicated of the
given species, neither will the genus be predicated of it; e.g. of
'soul' neither 'odd' nor 'even' is predicated: neither therefore is
'number'. Moreover, see whether the species is naturally prior and
abolishes the genus along with itself: for the contrary is the general
view. Moreover, if it be possible for the genus stated, or for its
differentia, to be absent from the alleged species, e.g. for
'movement' to be absent from the 'soul', or 'truth and falsehood' from
'opinion', then neither of the terms stated could be its genus or
its differentia: for the general view is that the genus and the
differentia accompany the species, as long as it exists.
3
Look and see, also, if what is placed in the genus partakes or could
possibly partake of any contrary of the genus: for in that case the
same thing will at the same time partake of contrary things, seeing
that the genus is never absent from it, while it partakes, or can
possibly partake, of the contrary genus as well. Moreover, see whether
the species shares in any character which it is utterly impossible for
any member of the genus to have. Thus (e.g.) if the soul has a share
in life, while it is impossible for any number to live, then the
soul could not be a species of number.
You should look and see, also, if the species be a homonym of the
genus, and employ as your elementary principles those already stated
for dealing with homonymity: for the genus and the species are
synonymous.
Seeing that of every genus there is more than one species, look
and see if it be impossible that there should be another species
than the given one belonging to the genus stated: for if there
should be none, then clearly what has been stated could not be a genus
at all.
Look and see, also, if he has rendered as genus a metaphorical
expression, describing (e.g. 'temperance' as a 'harmony': a 'harmony':
for a genus is always predicated of its species in its literal
sense, whereas 'harmony' is predicated of temperance not in a
literal sense but metaphorically: for a harmony always consists in
notes.
Moreover, if there be any contrary of the species, examine it. The
examination may take different forms; first of all see if the contrary
as well be found in the same genus as the species, supposing the genus
to have no contrary; for contraries ought to be found in the same
genus, if there be no contrary to the genus. Supposing, on the other
hand, that there is a contrary to the genus, see if the contrary of
the species be found in the contrary genus: for of necessity the
contrary species must be in the contrary genus, if there be any
contrary to the genus. Each of these points is made plain by means
of induction. Again, see whether the contrary of the species be not
found in any genus at all, but be itself a genus, e.g. 'good': for
if this be not found in any genus, neither will its contrary be
found in any genus, but will itself be a genus, as happens in the case
of 'good' and 'evil': for neither of these is found in a genus, but
each of them is a genus. Moreover, see if both genus and species be
contrary to something, and one pair of contraries have an
intermediary, but not the other. For if the genera have an
intermediary, so should their species as well, and if the species
have, so should their genera as well, as is the case w
ith (1) virtue
and vice and (2) justice and injustice: for each pair has an
intermediary. An objection to this is that there is no intermediary
between health and disease, although there is one between evil and
good. Or see whether, though there be indeed an intermediary between
both pairs, i.e. both between the species and between the genera,
yet it be not similarly related, but in one case be a mere negation of
the extremes, whereas in the other case it is a subject. For the
general view is that the relation should be similar in both cases,
as it is in the cases of virtue and vice and of justice and injustice:
for the intermediaries between both are mere negations. Moreover,
whenever the genus has no contrary, look and see not merely whether
the contrary of the species be found in the same genus, but the
intermediate as well: for the genus containing the extremes contains
the intermediates as well, as (e.g.) in the case of white and black:
for 'colour' is the genus both of these and of all the intermediate
colours as well. An objection may be raised that 'defect' and 'excess'
are found in the same genus (for both are in the genus 'evil'),
whereas moderate amount', the intermediate between them, is found
not in 'evil' but in 'good'. Look and see also whether, while the
genus has a contrary, the species has none; for if the genus be
contrary to anything, so too is the species, as virtue to vice and
justice to injustice.
Likewise. also, if one were to look at other instances, one would
come to see clearly a fact like this. An objection may be raised in
the case of health and disease: for health in general is the
contrary of disease, whereas a particular disease, being a species
of disease, e.g. fever and ophthalmia and any other particular
disease, has no contrary.
If, therefore, you are demolishing a view, there are all these
ways in which you should make your examination: for if the aforesaid
characters do not belong to it, clearly what has been rendered is
not the genus. If, on the other hand, you are establishing a view,