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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.
Part 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