The Complete Aristotle (eng.)

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 been shown to be real); while if you
want to overthrow a view, ask what it is that is real if the thing
in question be real, for if we show that what follows from the
thing in question is unreal, we shall have demolished the thing in
question.
    Moreover, look at the time involved, to see if there be any
discrepancy anywhere: e.g. suppose a man to have stated that what
is being nourished of necessity grows: for animals are always of
necessity being nourished, but they do not always grow. Likewise,
also, if he has said that knowing is remembering: for the one is
concerned with past time, whereas the other has to do also with the
present and the future. For we are said to know things present and
future (e.g. that there will be an eclipse), whereas it is
impossible to remember anything save what is in the past.
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5
    Moreover, there is the sophistic turn of argument, whereby we
draw our opponent into the kind of statement against which we shall
be well supplied with lines of argument. This process is sometimes
a real necessity, sometimes an apparent necessity, sometimes
neither an apparent nor a real necessity. It is really necessary
whenever the answerer has denied any view that would be useful in
attacking the thesis, and the