8

  Of 'sameness' then, as has been said,' three senses are to be
distinguished. Now one way to confirm that the elements mentioned
above are those out of which and through which and to which
arguments proceed, is by induction: for if any one were to survey
propositions and problems one by one, it would be seen that each was
formed either from the definition of something or from its property or
from its genus or from its accident. Another way to confirm it is
through reasoning. For every predicate of a subject must of
necessity be either convertible with its subject or not: and if it
is convertible, it would be its definition or property, for if it
signifies the essence, it is the definition; if not, it is a property:
for this was what a property is, viz. what is predicated
convertibly, but does not signify the essence. If, on the other
hand, it is not predicated convertibly of the thing, it either is or
is not one of the terms contained in the definition of the subject:
and if it be one of those terms, then it will be the genus or the
differentia, inasmuch as the definition consists of genus and
differentiae; whereas, if it be not one of those terms, clearly it
would be an accident, for accident was said' to be what belongs as
an attribute to a subject without being either its definition or its
genus or a property.

                                 9

  Next, then, we must distinguish between the classes of predicates in
which the four orders in question are found. These are ten in
number: Essence, Quantity, Quality, Relation, Place, Time, Position,
State, Activity, Passivity. For the accident and genus and property
and definition of anything will always be in one of these
categories: for all the propositions found through these signify
either something's essence or its quality or quantity or some one of
the other types of predicate. It is clear, too, on the face of it that
the man who signifies something's essence signifies sometimes a
substance, sometimes a quality, sometimes some one of the other
types of predicate. For when man is set before him and he says that
what is set there is 'a man' or 'an animal', he states its essence and
signifies a substance; but when a white colour is set before him and
he says that what is set there is 'white' or is 'a colour', he
states its essence and signifies a quality. Likewise, also, if a
magnitude of a cubit be set before him and he says that what is set
there is a magnitude of a cubit, he will be describing its essence and
signifying a quantity. Likewise, also, in the other cases: for each of
these kinds of predicate, if either it be asserted of itself, or its
genus be asserted of it, signifies an essence: if, on the other
hand, one kind of predicate is asserted of another kind, it does not
signify an essence, but a quantity or a quality or one of the other
kinds of predicate. Such, then, and so many, are the subjects on which
arguments take place, and the materials with which they start. How
we are to acquire them, and by what means we are to become well
supplied with them, falls next to be told.

                                10

  First, then, a definition must be given of a 'dialectical
proposition' and a 'dialectical problem'. For it is not every
proposition nor yet every problem that is to be set down as
dialectical: for no one in his senses would make a proposition of what
no one holds, nor yet make a problem of what is obvious to everybody
or to most people: for the latter admits of no doubt, while to the
former no one would assent. Now a dialectical proposition consists
in asking something that is held by all men or by most men or by the
philosophers, i.e. either by all, or by most, or by the most notable
of these, provided it be not contrary to the general opinion; for a
man would probably assent to the view of the philosophers, if it be
not contrary to the opinions of most men. Dialectical propositions
also include views which are like those generally accepted; also
propositions which contradict the contraries of opinions that are
taken to be generally accepted, and also all opinions that are in
accordance with the recognized arts. Thus, supposing it to be a
general opinion that the knowledge of contraries is the same, it might
probably pass for a general opinion also that the perception of
contraries is the same: also, supposing it to be a general opinion
that there is but one single science of grammar, it might pass for a
general opinion that there is but one science of flute-playing as
well, whereas, if it be a general opinion that there is more than
one science of grammar, it might pass for a general opinion that there
is more than one science of flute-playing as well: for all these
seem to be alike and akin. Likewise, also, propositions
contradicting the contraries of general opinions will pass as
general opinions: for if it be a general opinion that one ought to
do good to one's friends, it will also be a general opinion that one
ought not to do them harm. Here, that one ought to do harm to one's
friends is contrary to the general view, and that one ought not to
do them harm is the contradictory of that contrary. Likewise also,
if one ought to do good to one's friends, one ought not to do good
to one's enemies: this too is the contradictory of the view contrary
to the general view; the contrary being that one ought to do good to
one's enemies. Likewise, also, in other cases. Also, on comparison, it
will look like a general opinion that the contrary predicate belongs
to the contrary subject: e.g. if one ought to do good to one's
friends, one ought also to do evil to one's enemies. it might appear
also as if doing good to one's friends were a contrary to doing evil
to one's enemies: but whether this is or is not so in reality as
well will be stated in the course of the discussion upon contraries.
Clearly also, all opinions that are in accordance with the arts are
dialectical propositions; for people are likely to assent to the views
held by those who have made a study of these things, e.g. on a
question of medicine they will agree with the doctor, and on a