The Complete Aristotle (eng.)

is not to
be done in every case, but only whenever we are not easily able to
quote any single argument applying to all cases in common, as
(e.g.) the geometrician can argue that the triangle has its angles
equal to two right angles.
    If, again, the variety of meanings of a term be obvious,
distinguish how many meanings it has before proceeding either to
demolish or to establish it: e.g. supposing ‘the right’ to mean
‘the expedient’ or ‘the honourable’, you should try either to
establish or to demolish both descriptions of the subject in
question; e.g. by showing that it is honourable and expedient, or
that it is neither honourable nor expedient. Supposing, however,
that it is impossible to show both, you should show the one, adding
an indication that it is true in the one sense and not in the
other. The same rule applies also when the number of senses into
which it is divided is more than two.
    Again, consider those expressions whose meanings are many, but
differ not by way of ambiguity of a term, but in some other way:
e.g. ‘The science of many things is one’: here ‘many things’ may
mean the end and the means to that end, as (e.g.) medicine is the
science both of producing health and of dieting; or they may be
both of them ends, as the science of contraries is said to be the
same (for of contraries the one is no more an end than the other);
or again they may be an essential and an accidental attribute, as
(e.g.) the essential fact that the triangle has its angles equal to
two right angles, and the accidental fact that the equilateral
figure has them so: for it is because of the accident of the
equilateral triangle happening to be a triangle that we know that
it has its angles equal to two right angles. If, then, it is not
possible in any sense of the term that the science of many things
should be the same, it clearly is altogether impossible that it
should be so; or, if it is possible in some sense, then clearly it
is possible. Distinguish as many meanings as are required: e.g. if
we want to establish a view, we should bring forward all such
meanings as admit that view and should divide them only into those
meanings which also are required for the establishment of our case:
whereas if we want to overthrow a view, we should bring forward all
that do not admit that view, and leave the rest aside. We must deal
also in these cases as well with any uncertainty about the number
of meanings involved. Further, that one thing is, or is not, ‘of’
another should be established by means of the same commonplace
rules; e.g. that a particular science is of a particular thing,
treated either as an end or as a means to its end, or as
accidentally connected with it; or again that it is not ‘of’ it in
any of the aforesaid ways. The same rule holds true also of desire
and all other terms that have more than one object. For the ‘desire
of X’ may mean the desire of it as an end (e.g. the desire of
health) or as a means to an end (e.g. the desire of being
doctored), or as a thing desired accidentally, as, in the case of
wine, the sweet-toothed person desires it not because it is wine
but because it is sweet. For essentially he desires the sweet, and
only accidentally the wine: for if it be dry, he no longer desires
it. His desire for it is therefore accidental. This rule is useful
in dealing with relative terms: for cases of this kind are
generally cases of relative terms.
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4
    Moreover, it is well to alter a term into one more familiar,
e.g. to substitute ‘clear’ for ‘exact’ in describing a conception,
and ‘being fussy’ for ‘being busy’: for when the expression is made
more familiar, the thesis becomes easier to attack. This
commonplace rule also is available for both purposes alike, both
for establishing and for overthrowing a view.
    In order to show that contrary attributes belong to the same
thing, look at its genus; e.g. if we want to show that rightness
and wrongness are possible in regard to perception, and to perceive
is to judge, while it is possible to judge rightly or wrongly, then
in regard to perception as well rightness and wrongness must be
possible. In the present instance the proof proceeds from the genus
and relates to the species: for ‘to judge’ is the genus of ‘to
—perceive’; for the man who perceives judges in a certain way. But
per contra it may proceed from the species to the genus: for all
the attributes that