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Part 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
belong to the species belong to the genus as well; e.g. if there is a
bad and a good knowledge there is also a bad and a good disposition:
for 'disposition' is the genus of knowledge. Now the former
commonplace argument is fallacious for purposes of establishing a
view, while the second is true. For there is no necessity that all the
attributes that belong to the genus should belong also to the species;
for 'animal' is flying and quadruped, but not so 'man'. All the
attributes, on the other hand, that belong to the species must of
necessity belong also to the genus; for if 'man' is good, then animal
also is good. On the other hand, for purposes of overthrowing a view,
the former argument is true while the latter is fallacious; for all
the attributes which do not belong to the genus do not belong to the
species either; whereas all those that are wanting to the species are
not of necessity wanting to the genus.
Since those things of which the genus is predicated must also of
necessity have one of its species predicated of them, and since those
things that are possessed of the genus in question, or are described
by terms derived from that genus, must also of necessity be possessed
of one of its species or be described by terms derived from one of its
species (e.g. if to anything the term 'scientific knowledge' be
applied, then also there will be applied to it the term 'grammatical'
or 'musical' knowledge, or knowledge of one of the other sciences; and
if any one possesses scientific knowledge or is described by a term
derived from 'science', then he will also possess grammatical or
musical knowledge or knowledge of one of the other sciences, or will
be described by a term derived from one of them, e.g. as a
'grammarian' or a 'musician')-therefore if any expression be asserted
that is in any way derived from the genus (e.g. that the soul is in
motion), look and see whether it be possible for the soul to be moved
with any of the species of motion; whether (e.g.) it can grow or be
destroyed or come to be, and so forth with all the other species of
motion. For if it be not moved in any of these ways, clearly it does
not move at all. This commonplace rule is common for both purposes,
both for overthrowing and for establishing a view: for if the soul
moves with one of the species of motion, clearly it does move; while
if it does not move with any of the species of motion, clearly it does
not move.
If you are not well equipped with an argument against the assertion,
look among the definitions, real or apparent, of the thing before you,
and if one is not enough, draw upon several. For it will be easier to
attack people when committed to a definition: for an attack is always
more easily made on definitions.
Moreover, look and see in regard to the thing in question, what it is
whose reality conditions the reality of the thing in question, or what
it is whose reality necessarily follows if the thing in question be
real: if you wish to establish a view inquire what there is on whose
reality the reality of the thing in question will follow (for if the
former be shown to be real, then the thing in question will also have