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or no: for into questions of that kind too it is possible to inquire.
Problems, then, and propositions are to be defined as aforesaid. A
'thesis' is a supposition of some eminent philosopher that conflicts
with the general opinion; e.g. the view that contradiction is
impossible, as Antisthenes said; or the view of Heraclitus that all
things are in motion; or that Being is one, as Melissus says: for to
take notice when any ordinary person expresses views contrary to men's
usual opinions would be silly. Or it may be a view about which we have
a reasoned theory contrary to men's usual opinions, e.g. the view
maintained by the sophists that what is need not in every case either
have come to be or be eternal: for a musician who is a grammarian 'is'
so without ever having 'come to be' so, or being so eternally. For
even if a man does not accept this view, he might do so on the ground
that it is reasonable.
Now a 'thesis' also is a problem, though a problem is not always a
thesis, inasmuch as some problems are such that we have no opinion
about them either way. That a thesis, however, also forms a problem,
is clear: for it follows of necessity from what has been said that
either the mass of men disagree with the philosophers about the
thesis, or that the one or the other class disagree among themselves,
seeing that the thesis is a supposition in conflict with general
opinion. Practically all dialectical problems indeed are now called
'theses'. But it should make no difference whichever description is
used; for our object in thus distinguishing them has not been to
create a terminology, but to recognize what differences happen to be
found between them.
Not every problem, nor every thesis, should be examined, but only one
which might puzzle one of those who need argument, not punishment or
perception. For people who are puzzled to know whether one ought to
honour the gods and love one's parents or not need punishment, while
those who are puzzled to know whether snow is white or not need
perception. The subjects should not border too closely upon the sphere
of demonstration, nor yet be too far removed from it: for the former
cases admit of no doubt, while the latter involve difficulties too
great for the art of the trainer.
Part 12
Having drawn these definitions, we must distinguish how many species
there are of dialectical arguments. There is on the one hand
Induction, on the other Reasoning. Now what reasoning is has been said
before: induction is a passage from individuals to universals, e.g.
the argument that supposing the skilled pilot is the most effective,
and likewise the skilled charioteer, then in general the skilled man
is the best at his particular task. Induction is the more convincing
and clear: it is more readily learnt by the use of the senses, and is
applicable generally to the mass of men, though reasoning is more
forcible and effective against contradictious people.
Part 13
The classes, then, of things about which, and of things out of which,
arguments are constructed, are to be distinguished in the way we have
said before. The means whereby we are to become well supplied with
reasonings are four: (1) the securing of propositions; (2) the power
to distinguish in how many senses particular expression is used; (3)
the discovery of the differences of things; (4) the investigation of
likeness. The last three, as well, are in a certain sense
propositions: for it is possible to make a proposition corresponding
to each of them, e.g. (1) 'The desirable may mean either the
honourable or the pleasant or the expedient'; and (2) Sensation
differs from knowledge in that the latter may be recovered again after
it has been lost, while the former cannot'; and (3) The relation of
the healthy to health is like that of the vigorous to vigour'. The
first proposition depends upon the use of one term in several senses,
the second upon the differences of things, the third upon their
likenesses.
Part 14