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senses. Of course, in overthrowing a statement there is no need to
start the discussion by securing any admission, either when the
statement asserts or when it denies the attribute universally: for if
we show that in any case whatever the attribute does not belong, we
shall have demolished the universal assertion of it, and likewise also
if we show that it belongs in a single case, we shall demolish the
universal denial of it. Whereas in establishing a statement we ought
to secure a preliminary admission that if it belongs in any case
whatever, it belongs universally, supposing this claim to be a
plausible one. For it is not enough to discuss a single instance in
order to show that an attribute belongs universally; e.g. to argue
that if the soul of man be immortal, then every soul is immortal, so
that a previous admission must be secured that if any soul whatever be
immortal, then every soul is immortal. This 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.