BODY AND PRACTICE IN KANT

64
BODY AND SPACE
here which is Kant’s view on the embodied basis of spatial
experience. 7
A central problem for those interested in the embodied basis of spatial
experience was to explain the fact that we experience visual space as
three-dimensional. The seventeenth and eighteenth-century natural
philosophers understood the internal structure of the eye very well and
knew that visual images were produced by rays of light affecting the
retina. But as the retina is two-dimensional, how can rays of light
affecting it produce three-dimensional visual images? Berkeley presents a
version of this problem in his Essay towards a new theory of vision from
1709 thus:
It is, I think, agreed by all that Distance of it self, and immediately
cannot be seen. For Distance being a Line directed end-wise to the
Eye, it projects only one Point in the Fund of the Eye. Which Point
remains invariably the same, whether the Distance be longer or
shorter. 8
A ray of light will always hit the retina at one point only, Berkeley argues,
and whether the ray originates from near or far makes no difference.
How, then, do we see things to be either near or far away? How do we
visually perceive distance, and so three-dimensional space?
In suggesting solutions to this problem, most natural philosophers in
one way or another resorted to our capacity for moving our bodies. A
famous example is supplied by Étienne Bonnet de Condillac (1715-1780)
in his work Traité des sensations from 1754. Here he imagined a marble
statue internally constituted like a living human being, but having a mind
deprived of all ideas, and with all its senses closed, so that it would be
possible to open them one at a time and to analyze their relationship.
Condillac argued that hearing, taste, and sight would produce in the
statue no idea of exteriority. To show how the perception of
phenomenological exteriority arises, he therefore added to the statue the
sense of touch. The term le toucher used by Condillac includes a number
of elements, such as the awareness we have of processes internal to the
7 I do not intend to give anything like a complete account of the discussion taking
place between philosophers and scientists of the eighteenth century focusing on
the embodied aspect of spatial experience, but only enough to serve as a
background. A brief but still excellent survey of some main lines of this debate is
found in Kitcher, which also serves as a basis for the following exposition, cf.
Kitcher (1990), and also Herrnstein (1968).
8 Quoted from Herrnstein (1968), 118.