The Complete Aristotle (eng.)

overthrowing it, it is enough to
show its failure to belong either in some particular case or in
every case. It appears, in fact, as though, just as in other things
to destroy is easier than to create, so in these matters too to
overthrow is easier than to establish.
    In the case of an accidental attribute the universal proposition
is easier to overthrow than to establish; for to establish it, one
has to show that it belongs in every case, whereas to overthrow it,
it is enough to show that it does not belong in one single case.
The particular proposition is, on the contrary, easier to establish
than to overthrow: for to establish it, it is enough to show that
it belongs in a particular instance, whereas to overthrow it, it
has to be shown that it never belongs at all.
    It is clear also that the easiest thing of all is to overthrow a
definition. For on account of the number of statements involved we
are presented in the definition with the greatest number of points
for attack, and the more plentiful the material, the quicker an
argument comes: for there is more likelihood of a mistake occurring
in a large than in a small number of things. Moreover, the other
rules too may be used as means for attacking a definition: for if
either the formula be not peculiar, or the genus rendered be the
wrong one, or something included in the formula fail to belong, the
definition is thereby demolished. On the other hand, against the
others we cannot bring all of the arguments drawn from definitions,
nor yet of the rest: for only those relating to accidental
attributes apply generally to all the aforesaid kinds of attribute.
For while each of the aforesaid kinds of attribute must belong to
the thing in question, yet the genus may very well not belong as a
property without as yet being thereby demolished. Likewise also the
property need not belong as a genus, nor the accident as a genus or
property, so long as they do belong. So that it is impossible to
use one set as a basis of attack upon the other except in the case
of definition. Clearly, then, it is the easiest of all things to
demolish a definition, while to establish one is the hardest. For
there one both has to establish all those other points by reasoning
(i.e. that the attributes stated belong, and that the genus
rendered is the true genus, and that the formula is peculiar to the
term), and moreover, besides this, that the formula indicates the
essence of the thing; and this has to be done correctly.
    Of the rest, the property is most nearly of this kind: for it is
easier to demolish, because as a rule it contains several terms;
while it is the hardest to establish, both because of the number of
things that people must be brought to accept, and, besides this,
because it belongs to its subject alone and is predicated
convertibly with its subject.
    The easiest thing of all to establish is an accidental
predicate: for in other cases one has to show not only that the
predicate belongs, but also that it belongs in such and such a
particular way: whereas in the case of the accident it is enough to
show merely that it belongs. On the other hand, an accidental
predicate is the hardest thing to overthrow, because it affords the
least material: for in stating accident a man does not add how the
predicate belongs; and accordingly, while in other cases it is
possible to demolish what is said in two ways, by showing either
that the predicate does not belong, or that it does not belong in
the particular way stated, in the case of an accidental predicate
the only way to demolish it is to show that it does not belong at
all.
    The commonplace arguments through which we shall be well
supplied with lines of argument with regard to our several problems
have now been enumerated at about sufficient length.

Topics, Book VIII
    Translated by W. A. Pickard-Cambridge
<
    div id="book8" class="book" title="Book VIII">
    1
    Next there fall to be discussed the problems of arrangement and
method in putting questions. Any one who intends to frame questions
must, first of all, select the ground from which he should make his
attack; secondly, he must frame them and arrange them one by one to
himself; thirdly and lastly, he must proceed actually to put them
to the other party. Now so far as the selection of his ground is
concerned the problem is one alike for the philosopher and the
dialectician; but how to go on to arrange his points and frame his
questions concerns the dialectician only: for in every problem