Aristotle

by Various Works [lit]

  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,