Moreover, see if there be anything of which the species rendered
is true, while the genus is not so, e.g. supposing 'being' or
'object of knowledge' were stated to be the genus of 'object of
opinion'. For 'object of opinion' will be a predicate of what does not
exist; for many things which do not exist are objects of opinion;
whereas that 'being' or 'object of knowledge' is not predicated of
what does not exist is clear. So that neither 'being' nor 'object of
knowledge' is the genus of 'object of opinion': for of the objects
of which the species is predicated, the genus ought to be predicated
as well.
Again, see whether the object placed in the genus be quite unable to
partake of any of its species: for it is impossible that it should
partake of the genus if it do not partake of any of its species,
except it be one of the species reached by the first division: these
do partake of the genus alone. If, therefore, 'Motion' be stated as
the genus of pleasure, you should look and see if pleasure be
neither locomotion nor alteration, nor any of the rest of the given
modes of motion: for clearly you may then take it that it does not
partake of any of the species, and therefore not of the genus
either, since what partakes of the genus must necessarily partake of
one of the species as well: so that pleasure could not be a species of
Motion, nor yet be one of the individual phenomena comprised under the
term 'motion'.
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