by Aristotle
for it is not easy to do this if we do not know the points of
likeness. It is useful for hypothetical reasonings because it is a
general opinion that among similars what is true of one is true also
of the rest. If, then, with regard to any of them we are well supplied
with matter for a discussion, we shall secure a preliminary
admission that however it is in these cases, so it is also in the case
before us: then when we have shown the former we shall have shown,
on the strength of the hypothesis, the matter before us as well: for
we have first made the hypothesis that however it is in these cases,
so it is also in the case before us, and have then proved the point as
regards these cases. It is useful for the rendering of definitions
because, if we are able to see in one glance what is the same in
each individual case of it, we shall be at no loss into what genus
we ought to put the object before us when we define it: for of the
common predicates that which is most definitely in the category of
essence is likely to be the genus. Likewise, also, in the case of
objects widely divergent, the examination of likeness is useful for
purposes of definition, e.g. the sameness of a calm at sea, and
windlessness in the air (each being a form of rest), and of a point on
a line and the unit in number-each being a starting point. If, then,
we render as the genus what is common to all the cases, we shall get
the credit of defining not inappropriately. Definition-mongers too
nearly always render them in this way: they declare the unit to be the
startingpoint of number, and the point the startingpoint of a line. It
is clear, then, that they place them in that which is common to both
as their genus.
The means, then, whereby reasonings are effected, are these: the
commonplace rules, for the observance of which the aforesaid means are
useful, are as follows.
Book II
1
Of problems some are universal, others particular. Universal
problems are such as 'Every pleasure is good' and 'No pleasure is
good'; particular problems are such as 'Some pleasure is good' and
'Some pleasure is not good'. The methods of establishing and
overthrowing a view universally are common to both kinds of
problems; for when we have shown that a predicate belongs in every
case, we shall also have shown that it belongs in some cases.
Likewise, also, if we show that it does not belong in any case, we
shall also have shown that it does not belong in every case. First,
then, we must speak of the methods of overthrowing a view universally,
because such are common to both universal and particular problems, and
because people more usually introduce theses asserting a predicate
than denying it, while those who argue with them overthrow it. The
conversion of an appropriate name which is drawn from the element
'accident' is an extremely precarious thing; for in the case of
accidents and in no other it is possible for something to be true
conditionally and not universally. Names drawn from the elements
'definition' and 'property' and 'genus' are bound to be convertible;
e.g. if 'to be an animal that walks on two feet is an attribute of S',
then it will be true by conversion to say that 'S is an animal that
walks on two feet'. Likewise, also, if drawn from the genus; for if
'to be an animal is an attribute of S', then 'S is an animal'. The
same is true also in the case of a property; for if 'to be capable
of learning grammar is an attribute of S', then 'S will be capable
of learning grammar'. For none of these attributes can possibly belong
or not belong in part; they must either belong or not belong
absolutely. In the case of accidents, on the other hand, there is
nothing to prevent an attribute (e.g. whiteness or justice)
belonging in part, so that it is not enough to show that whiteness
or justice is an attribute of a man in order to show that he is
white or just; for it is open to dispute it and say that he is white
or just in part only. Conversion, then, is not a necessary process
in the case of accidents.
We must also define the errors that occur in problems. They are of
two kinds, caused either by false statement or by transgression of the
established diction. For those who make false statements, and say that
an attribute belongs to thing which does not belong to it, commit
error; and those who call objects by the names of other objects
(e.g. calling a planetree a 'man') transgress the established
terminology.
2
Now one commonplace rule is to look and see if a man has ascribed as
an accident what belongs in some other way. This mistake is most
commonly made in regard to the genera of things, e.g. if one were to
say that white happens (accidit) to be a colour-for being a colour
does not happen by accident to white, but colour is its genus. The
assertor may of course define it so in so many words, saying (e.g.)
that 'Justice happens (accidit) to be a virtue'; but often even
without such definition it is obvious that he has rendered the genus
as an accident; e.g. suppose that one were to say that whiteness is
coloured or that walking is in motion. For a predicate drawn from
the genus is never ascribed to the species in an inflected form, but
always the genera are predicated of their species literally; for the
species take on both the name and the definition of their genera. A
man therefore who says that white is 'coloured' has not rendered
'coloured' as its genus, seeing that he has used an inflected form,
nor yet as its property or as its definition: for the definition and
property of a thing belong to it and to nothing else, whereas many
things besides white are coloured, e.g. a log, a stone, a man, and a
horse. Clearly then he renders it as an accident.
Another rule is to examine all cases where a predicate has been
either asserted or denied universally to belong to something. Look
at them species by species, and not in their infinite multitude: for
then the inquiry will proceed more directly and in fewer steps. You
should look and begin with the most primary groups, and then proceed
in order down to those that are not further divisible: e.g. if a man
has said that the knowledge of opposites is the same, you should
look and see whether it be so of relative opposites and of
contraries and of terms signifying the privation or presence of
certain states, and of contradictory terms. Then, if no clear result
be reached so far in these cases, you should again divide these
until you come to those that are not further divisible, and see (e.g.)
whether it be so of just deeds and unjust, or of the double and the
half, or of blindness and sight, or of being and not-being: for if
in any case it be shown that the knowledge of them is not the same
we shall have demolished the problem. Likewise, also, if the predicate
belongs in no case. This rule is convertible for both destructive
and constructive purposes: for if, when we have suggested a
divisi
on, the predicate appears to hold in all or in a large number of
cases, we may then claim that the other should actually assert it
universally, or else bring a negative instance to show in what case it
is not so: for if he does neither of these things, a refusal to assert
it will make him look absurd.
Another rule is to make definitions both of an accident and of its
subject, either of both separately or else of one of them, and then
look and see if anything untrue has been assumed as true in the
definitions. Thus (e.g.) to see if it is possible to wrong a god,
ask what is 'to wrong'? For if it be 'to injure deliberately', clearly
it is not possible for a god to be wronged: for it is impossible
that God should be injured. Again, to see if the good man is
jealous, ask who is the 'jealous' man and what is 'jealousy'. For if
'jealousy' is pain at the apparent success of some well-behaved
person, clearly the good man is not jealous: for then he would be bad.
Again, to see if the indignant man is jealous, ask who each of them
is: for then it will be obvious whether the statement is true or
false; e.g. if he is 'jealous' who grieves at the successes of the
good, and he is 'indignant' who grieves at the successes of the
evil, then clearly the indignant man would not be jealous. A man
should substitute definitions also for the terms contained in his
definitions, and not stop until he comes to a familiar term: for often
if the definition be rendered whole, the point at issue is not cleared
up, whereas if for one of the terms used in the definition a
definition be stated, it becomes obvious.
Moreover, a man should make the problem into a proposition for
himself, and then bring a negative instance against it: for the
negative instance will be a ground of attack upon the assertion.
This rule is very nearly the same as the rule to look into cases where
a predicate has been attributed or denied universally: but it
differs in the turn of the argument.
Moreover, you should define what kind of things should be called
as most men call them, and what should not. For this is useful both
for establishing and for overthrowing a view: e.g. you should say that
we ought to use our terms to mean the same things as most people
mean by them, but when we ask what kind of things are or are not of
such and such a kind, we should not here go with the multitude: e.g.
it is right to call 'healthy' whatever tends to produce health, as
do most men: but in saying whether the object before us tends to
produce health or not, we should adopt the language no longer of the
multitude but of the doctor.
3
Moreover, if a term be used in several senses, and it has been
laid down that it is or that it is not an attribute of S, you should
show your case of one of its several senses, if you cannot show it
of both. This rule is to be observed in cases where the difference
of meaning is undetected; for supposing this to be obvious, then the
other man will object that the point which he himself questioned has
not been discussed, but only the other point. This commonplace rule is
convertible for purposes both of establishing and of overthrowing a
view. For if we want to establish a statement, we shall show that in
one sense the attribute belongs, if we cannot show it of both
senses: whereas if we are overthrowing a statement, we shall show that
in one sense the attribute does not belong, if we cannot show it of
both senses. Of course, in overthrowing a statement there is no need
to start the discussion by securing any admission, either when the
statement asserts or when it denies the attribute universally: for
if we show that in any case whatever the attribute does not belong, we
shall have demolished the universal assertion of it, and likewise also
if we show that it belongs in a single case, we shall demolish the
universal denial of it. Whereas in establishing a statement we ought
to secure a preliminary admission that if it belongs in any case
whatever, it belongs universally, supposing this claim to be a
plausible one. For it is not enough to discuss a single instance in
order to show that an attribute belongs universally; e.g. to argue
that if the soul of man be immortal, then every soul is immortal, so
that a previous admission must be secured that if any soul whatever be
immortal, then every soul is immortal. This is not to be done in every
case, but only whenever we are not easily able to quote any single
argument applying to all cases in common, as (e.g.) the geometrician
can argue that the triangle has its angles equal to two right angles.
If, again, the variety of meanings of a term be obvious, distinguish
how many meanings it has before proceeding either to demolish or to
establish it: e.g. supposing 'the right' to mean 'the expedient' or
'the honourable', you should try either to establish or to demolish
both descriptions of the subject in question; e.g. by showing that
it is honourable and expedient, or that it is neither honourable nor
expedient. Supposing, however, that it is impossible to show both, you
should show the one, adding an indication that it is true in the one
sense and not in the other. The same rule applies also when the number
of senses into which it is divided is more than two.
Again, consider those expressions whose meanings are many, but
differ not by way of ambiguity of a term, but in some other way:
e.g. 'The science of many things is one': here 'many things' may
mean the end and the means to that end, as (e.g.) medicine is the
science both of producing health and of dieting; or they may be both
of them ends, as the science of contraries is said to be the same (for
of contraries the one is no more an end than the other); or again they
may be an essential and an accidental attribute, as (e.g.) the
essential fact that the triangle has its angles equal to two right
angles, and the accidental fact that the equilateral figure has them
so: for it is because of the accident of the equilateral triangle
happening to be a triangle that we know that it has its angles equal
to two right angles. If, then, it is not possible in any sense of
the term that the science of many things should be the same, it
clearly is altogether impossible that it should be so; or, if it is
possible in some sense, then clearly it is possible. Distinguish as
many meanings as are required: e.g. if we want to establish a view, we
should bring forward all such meanings as admit that view and should
divide them only into those meanings which also are required for the
establishment of our case: whereas if we want to overthrow a view,
we should bring forward all that do not admit that view, and leave the
rest aside. We must deal also in these cases as well with any
uncertainty about the number of meanings involved. Further, that one
thing is, or is not, 'of' another should be established by means of
the same commonplace rules; e.g. that a particular science is of a
particular thing, treated either as an end or a
s a means to its end,
or as accidentally connected with it; or again that it is not 'of'
it in any of the aforesaid ways. The same rule holds true also of
desire and all other terms that have more than one object. For the
'desire of X' may mean the desire of it as an end (e.g. the desire
of health) or as a means to an end (e.g. the desire of being
doctored), or as a thing desired accidentally, as, in the case of
wine, the sweet-toothed person desires it not because it is wine but
because it is sweet. For essentially he desires the sweet, and only
accidentally the wine: for if it be dry, he no longer desires it.
His desire for it is therefore accidental. This rule is useful in
dealing with relative terms: for cases of this kind are generally
cases of relative terms.
4
Moreover, it is well to alter a term into one more familiar, e.g. to
substitute 'clear' for 'exact' in describing a conception, and
'being fussy' for 'being busy': for when the expression is made more
familiar, the thesis becomes easier to attack. This commonplace rule
also is available for both purposes alike, both for establishing and
for overthrowing a view.
In order to show that contrary attributes belong to the same
thing, look at its genus; e.g. if we want to show that rightness and
wrongness are possible in regard to perception, and to perceive is
to judge, while it is possible to judge rightly or wrongly, then in
regard to perception as well rightness and wrongness must be possible.
In the present instance the proof proceeds from the genus and
relates to the species: for 'to judge' is the genus of 'to -perceive';
for the man who perceives judges in a certain way. But per contra it
may proceed from the species to the genus: for all the attributes that
belong to the species belong to the genus as well; e.g. if there is
a bad and a good knowledge there is also a bad and a good disposition:
for 'disposition' is the genus of knowledge. Now the former
commonplace argument is fallacious for purposes of establishing a