The Complete Aristotle (eng.)

irrefutable.
    Moreover, whenever one foresees any question coming, one should
put in one’s objection and have one’s say beforehand: for by doing
so one is likely to embarrass the questioner most effectually.
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    Inasmuch as a proper solution is an exposure of false reasoning,
showing on what kind of question the falsity depends, and whereas
‘false reasoning’ has a double meaning-for it is used either if a
false conclusion has been proved, or if there is only an apparent
proof and no real one-there must be both the kind of solution just
described,’ and also the correction of a merely apparent proof, so
as to show upon which of the questions the appearance depends. Thus
it comes about that one solves arguments that are properly reasoned
by demolishing them, whereas one solves merely apparent arguments
by drawing distinctions. Again, inasmuch as of arguments that are
properly reasoned some have a true and others a false conclusion,
those that are false in respect of their conclusion it is possible
to solve in two ways; for it is possible both by demolishing one of
the premisses asked, and by showing that the conclusion is not the
real state of the case: those, on the other hand, that are false in
respect of the premisses can be solved only by a demolition of one
of them; for the conclusion is true. So that those who wish to
solve an argument should in the first place look and see if it is
properly reasoned, or is unreasoned; and next, whether the
conclusion be true or false, in order that we may effect the
solution either by drawing some distinction or by demolishing
something, and demolishing it either in this way or in that, as was
laid down before. There is a very great deal of difference between
solving an argument when being subjected to questions and when not:
for to foresee traps is difficult, whereas to see them at one’s
leisure is easier.
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    Of the refutations, then, that depend upon ambiguity and
amphiboly some contain some question with more than one meaning,
while others contain a conclusion bearing a number of senses: e.g.
in the proof that ‘speaking of the silent’ is possible, the
conclusion has a double meaning, while in the proof that ‘he who
knows does not understand what he knows’ one of the questions
contains an amphiboly. Also the double-edged saying is true in one
context but not in another: it means something that is and
something that is not.
    Whenever, then, the many senses lie in the conclusion no
refutation takes place unless the sophist secures as well the
contradiction of the conclusion he means to prove; e.g. in the
proof that ‘seeing of the blind’ is possible: for without the
contradiction there was no refutation. Whenever, on the other hand,
the many senses lie in the questions, there is no necessity to
begin by denying the double-edged premiss: for this was not the
goal of the argument but only its support. At the start, then, one
should reply with regard to an ambiguity, whether of a term or of a
phrase, in this manner, that ‘in one sense it is so, and in another
not so’, as e.g. that ‘speaking of the silent’ is in one sense
possible but in another not possible: also that in one sense ‘one
should do what must needs be done’, but not in another: for ‘what
must needs be’ bears a number of senses. If, however, the ambiguity
escapes one, one should correct it at the end by making an addition
to the question: ‘Is speaking of the silent possible?’ ‘No, but to
speak of while he is silent is possible.’ Also, in cases which
contain the ambiguity in their premisses, one should reply in like
manner: ‘Do people-then not understand what they know? “Yes, but
not those who know it in the manner described’: for it is not the
same thing to say that ‘those who know cannot understand what they
know’, and to say that ‘those who know something in this particular
manner cannot do so’. In general, too, even though he draws his
conclusion in a quite unambiguous manner, one should contend that
what he has negated is not the fact which one has asserted but only
its name; and that therefore there is no refutation.
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    It is evident also how one should solve those refutations that
depend upon the division and combination of words: for if the
expression means something different when divided and