The Complete Aristotle (eng.)

questioner thereupon addresses his
arguments to the support of this view, and when moreover the view
in question happens to be one of a kind on which he has a good
stock of lines of argument. Likewise, also, it is really necessary
whenever he (the questioner) first, by an induction made by means
of the view laid down, arrives at a certain statement and then
tries to demolish that statement: for when once this has been
demolished, the view originally laid down is demolished as well. It
is an apparent necessity, when the point to which the discussion
comes to be directed appears to be useful, and relevant to the
thesis, without being really so; whether it be that the man who is
standing up to the argument has refused to concede something, or
whether he (the questioner) has first reached it by a plausible
induction based upon the thesis and then tries to demolish it. The
remaining case is when the point to which the discussion comes to
be directed is neither really nor apparently necessary, and it is
the answerer’s luck to be confuted on a mere side issue You should
beware of the last of the aforesaid methods; for it appears to be
wholly disconnected from, and foreign to, the art of dialectic. For
this reason, moreover, the answerer should not lose his temper, but
assent to those statements that are of no use in attacking the
thesis, adding an indication whenever he assents although he does
not agree with the view. For, as a rule, it increases the confusion
of questioners if, after all propositions of this kind have been
granted them, they can then draw no conclusion.
    Moreover, any one who has made any statement whatever has in a
certain sense made several statements, inasmuch as each statement
has a number of necessary consequences: e.g. the man who said ‘X is
a man’ has also said that it is an animal and that it is animate
and a biped and capable of acquiring reason and knowledge, so that
by the demolition of any single one of these consequences, of
whatever kind, the original statement is demolished as well. But
you should beware here too of making a change to a more difficult
subject: for sometimes the consequence, and sometimes the original
thesis, is the easier to demolish.
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6
    In regard to subjects which must have one and one only of two
predicates, as (e.g.) a man must have either a disease or health,
supposing we are well supplied as regards the one for arguing its
presence or absence, we shall be well equipped as regards the
remaining one as well. This rule is convertible for both purposes:
for when we have shown that the one attribute belongs, we shall
have shown that the remaining one does not belong; while if we show
that the one does not belong, we shall have shown that the
remaining one does belong. Clearly then the rule is useful for both
purposes.
    Moreover, you may devise a line of attack by reinterpreting a
term in its literal meaning, with the implication that it is most
fitting so to take it rather than in its established meaning: e.g.
the expression ‘strong at heart’ will suggest not the courageous
man, according to the use now established, but the man the state of
whose heart is strong; just as also the expression ‘of a good hope’
may be taken to mean the man who hopes for good things. Likewise
also ‘well-starred’ may be taken to mean the man whose star is
good, as Xenocrates says ‘well-starred is he who has a noble
soul’.’ For a man’s star is his soul.
    Some things occur of necessity, others usually, others however
it may chance; if therefore a necessary event has been asserted to
occur usually, or if a usual event (or, failing such an event
itself, its contrary) has been stated to occur of necessity, it
always gives an opportunity for attack. For if a necessary event
has been asserted to occur usually, clearly the speaker has denied
an attribute to be universal which is universal, and so has made a
mistake: and so he has if he has declared the usual attribute to be
necessary: for then he declares it to belong universally when it
does not so belong. Likewise also if he has declared the contrary
of what is usual to be necessary. For the contrary of a usual
attribute is always a comparatively rare attribute: e.g. if men are
usually bad, they are comparatively seldom good, so that his
mistake is even worse if he has declared them to be good of
necessity. The same is true also if he has declared a mere matter
of chance to