Topics   

Part 1

Our treatise proposes to find a line of inquiry whereby we shall be
able to reason from opinions that are generally accepted about every
problem propounded to us, and also shall ourselves, when standing up
to an argument, avoid saying anything that will obstruct us. First,
then, we must say what reasoning is, and what its varieties are, in
order to grasp dialectical reasoning: for this is the object of our
search in the treatise before us.
Now reasoning is an argument in which, certain things being laid down,
something other than these necessarily comes about through them. (a)
It is a 'demonstration', when the premisses from which the reasoning
starts are true and primary, or are such that our knowledge of them
has originally come through premisses which are primary and true: (b)
reasoning, on the other hand, is 'dialectical', if it reasons from
opinions that are generally accepted. Things are 'true' and 'primary'
which are believed on the strength not of anything else but of
themselves: for in regard to the first principles of science it is
improper to ask any further for the why and wherefore of them; each of
the first principles should command belief in and by itself. On the
other hand, those opinions are 'generally accepted' which are accepted
by every one or by the majority or by the philosophers-i.e. by all, or
by the majority, or by the most notable and illustrious of them. Again
(c), reasoning is 'contentious' if it starts from opinions that seem
to be generally accepted, but are not really such, or again if it
merely seems to reason from opinions that are or seem to be generally
accepted. For not every opinion that seems to be generally accepted
actually is generally accepted. For in none of the opinions which we
call generally accepted is the illusion entirely on the surface, as
happens in the case of the principles of contentious arguments; for
the nature of the fallacy in these is obvious immediately, and as a
rule even to persons with little power of comprehension. So then, of
the contentious reasonings mentioned, the former really deserves to be
called 'reasoning' as well, but the other should be called
'contentious reasoning', but not 'reasoning', since it appears to
reason, but does not really do so. Further (d), besides all the
reasonings we have mentioned there are the mis-reasonings that start
from the premisses peculiar to the special sciences, as happens (for
example) in the case of geometry and her sister sciences. For this
form of reasoning appears to differ from the reasonings mentioned
above; the man who draws a false figure reasons from things that are
neither true and primary, nor yet generally accepted. For he does not
fall within the definition; he does not assume opinions that are
received either by every one or by the majority or by
philosophers-that is to say, by all, or by most, or by the most
illustrious of them-but he conducts his reasoning upon assumptions
which, though appropriate to the science in question, are not true;
for he effects his mis-reasoning either by describing the semicircles
wrongly or by drawing certain lines in a way in which they could not
be drawn.
The foregoing must stand for an outline survey of the species of
reasoning. In general, in regard both to all that we have already
discussed and to those which we shall discuss later, we may remark
that that amount of distinction between them may serve, because it is
not our purpose to give the exact definition of any of them; we merely
want to describe them in outline; we consider it quite enough from the
point of view of the line of inquiry before us to be able to recognize
each of them in some sort of way.
Part 2
Next in order after the foregoing, we must say for how many and for
what purposes the treatise is useful. They are three-intellectual
training, casual encounters, and the philosophical sciences. That it