What sort of differences, indeed, might we use to establish such
divisions, and from what genus would we draw them? It seems absurd to
classify quality by quality itself. This is just as if the difference
of "beings" were to be called "beings." By what indeed could one
distinguish white from black, and colors from tastes and sensations
of touch? If we distinguish the difference of these qualities by the
sense-organs, these differences would no longer exist in the subjects.
How indeed could one and the same sense distinguish the difference of
the qualities it perceives? Is it because certain things exercise an
action that is constructive or destructive on the eyes, or the tongue?
We would then have to ask what is the constructive or destructive
element in the sensations thus excited? Yet, even were this answered,
such an answer would not explain wherein these things differ.[407]