C CUNYB/Clarke December, :
AFabulous World (–) The hypothesis suggested by Descartes to account for sight was that the
image formed on the retina causes a mechanically transmitted change in the
centre of the brain. This pulling motion results in a release of animal spirits
from the pineal gland in patterns that correspond, in some systematic way,
to the images formed inside the eye. Descartes then suggested that the word
‘idea’ should be applied to the shape, form, or pattern assumed by this
release of animal spirits. Descartes had argued, in theRules, that there is an
infinite supply of different geometrical shapes available by which one could
model all sensations. He returns to this point inThe Worldto suggest that
the ‘figures’ or ‘shapes’ assumed by animal spirits, in response to various
sensations, can vary systematically with the sensations themselves. These
patterns, therefore, can provide an occasion for a human being ‘to sense
movement, size, distance, colour, sounds, smells, and other such qualities;
and even things that can make it sense pleasure, pain, hunger, thirst, joy,
sadness, and other such passions’ (xi.).
It may come as a surprise that Descartes wanted to apply the term
‘idea’ to the flow patterns of animal spirits in the brain, but he is so
explicit about this that it is impossible to avoid the implications of his
claims. Objects that strike the senses cause many effects in the perceiver’s
body. However, ‘it is not those imprinted on the organs of external sense,
or on the inside surface of the brain, that should be taken as ideas, but
only those traced in the spirits on the surface of the pineal gland, where
the seat of the imagination and the common sense is’ (xi.). Once ideas
were understood as patterns in the flow of animal spirits to and from the
brain, it was a short step to speculate about the imagination and memory
as brain processes that resemble what happens in perception. Imagination
is understood as an activity in the brain that results from those flows of
animal spirits that arise spontaneously when an animal is not sensing any
external stimuli; and memory is a disposition of the nerve ducts to conduct
the spirits in patterns that resemble previous patterns.
Descartes said at the outset of this treatise that he proposed to explain
the body first, and then the soul. Accordingly, he refers at various stages
to the addition of a ‘rational soul’ to the body and to the ways in which
the ‘soul’ functions in causing sensations.However, theTreatise on Man
concludes with an ambitious claim about the extent to which this rather
speculative, hydraulic model has provided explanations of every animal
function apart from those that are reserved for rational souls. Everything
else about animal life is explicable in principle along these lines, and the