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Propositions should be selected in a number of ways corresponding to
the number of distinctions drawn in regard to the proposition: thus
one may first take in hand the opinions held by all or by most men or
by the philosophers, i.e. by all, or most, or the most notable of
them; or opinions contrary to those that seem to be generally held;
and, again, all opinions that are in accordance with the arts. We must
make propositions also of the contradictories of opinions contrary to
those that seem to be generally held, as was laid down before. It is
useful also to make them by selecting not only those opinions that
actually are accepted, but also those that are like these, e.g. 'The
perception of contraries is the same'-the knowledge of them being
so-and 'we see by admission of something into ourselves, not by an
emission'; for so it is, too, in the case of the other senses; for in
hearing we admit something into ourselves; we do not emit; and we
taste in the same way. Likewise also in the other cases. Moreover, all
statements that seem to be true in all or in most cases, should be
taken as a principle or accepted position; for they are posited by
those who do not also see what exception there may be. We should
select also from the written handbooks of argument, and should draw up
sketch-lists of them upon each several kind of subject, putting them
down under separate headings, e.g. 'On Good', or 'On Life'-and that
'On Good' should deal with every form of good, beginning with the
category of essence. In the margin, too, one should indicate also the
opinions of individual thinkers, e.g. 'Empedocles said that the
elements of bodies were four': for any one might assent to the saying
of some generally accepted authority.
Of propositions and problems there are-to comprehend the matter in
outline-three divisions: for some are ethical propositions, some are
on natural philosophy, while some are logical. Propositions such as
the following are ethical, e.g. 'Ought one rather to obey one's
parents or the laws, if they disagree?'; such as this are logical,
e.g. 'Is the knowledge of opposites the same or not?'; while such as
this are on natural philosophy, e.g. 'Is the universe eternal or not?'
Likewise also with problems. The nature of each of the aforesaid kinds
of proposition is not easily rendered in a definition, but we have to
try to recognize each of them by means of the familiarity attained
through induction, examining them in the light of the illustrations
given above.
For purposes of philosophy we must treat of these things according to
their truth, but for dialectic only with an eye to general opinion.
All propositions should be taken in their most universal form; then,
the one should be made into many. E.g. 'The knowledge of opposites is
the same'; next, 'The knowledge of contraries is the same', and that
'of relative terms'. In the same way these two should again be
divided, as long as division is possible, e.g. the knowledge of 'good
and evil', of 'white and black', or 'cold and hot'. Likewise also in
other cases.
Part 15
On the formation, then, of propositions, the above remarks are enough.
As regards the number of senses a term bears, we must not only treat
of those terms which bear different senses, but we must also try to
render their definitions; e.g. we must not merely say that justice and
courage are called 'good' in one sense, and that what conduces to
vigour and what conduces to health are called so in another, but also
that the former are so called because of a certain intrinsic quality
they themselves have, the latter because they are productive of a
certain result and not because of any intrinsic quality in themselves.
Similarly also in other cases.
Whether a term bears a number of specific meanings or one only, may be
considered by the following means. First, look and see if its contrary
bears a number of meanings, whether the discrepancy between them be
one of kind or one of names. For in some cases a difference is at once
displayed even in the names; e.g. the contrary of 'sharp' in the case
of a note is 'flat', while in the case of a solid edge it is 'dull'.