On The Soul
yellowness of bile, the assertion of the identity of both cannot be
the act of either of the senses; hence the illusion of sense, e.g. the
belief that if a thing is yellow it is bile.
It might be asked why we have more senses than one. Is it to prevent
a failure to apprehend the common sensibles, e.g. movement, magnitude,
and number, which go along with the special sensibles? Had we no sense
but sight, and that sense no object but white, they would have
tended to escape our notice and everything would have merged for us
into an indistinguishable identity because of the concomitance of
colour and magnitude. As it is, the fact that the common sensibles are
given in the objects of more than one sense reveals their
distinction from each and all of the special sensibles.
Since it is through sense that we are aware that we are seeing or
hearing, it must be either by sight that we are aware of seeing, or by
some sense other than sight. But the sense that gives us this new
sensation must perceive both sight and its object, viz. colour: so
that either (1) there will be two senses both percipient of the same
sensible object, or (2) the sense must be percipient of itself.
Further, even if the sense which perceives sight were different from
sight, we must either fall into an infinite regress, or we must
somewhere assume a sense which is aware of itself. If so, we ought
to do this in the first case.
This presents a difficulty: if to perceive by sight is just to
see, and what is seen is colour (or the coloured), then if we are to
see that which sees, that which sees originally must be coloured. It
is clear therefore that 'to perceive by sight' has more than one
meaning; for even when we are not seeing, it is by sight that we
discriminate darkness from light, though not in the same way as we
distinguish one colour from another. Further, in a sense even that