Descartes began with the basic epistemological premise of every Witch Doctor (a
premise he shared explicitly with Augustine): “the prior certainty of
consciousness,” the belief that the existence of an external world is not
self-evident, but must be proved by deduction from the contents of one’s
consciousness—which means: the concept of consciousness as some faculty other
than the faculty of perception—which means: the indiscriminate contents of
one’s consciousness as the irreducible primary and absolute, to which reality
has to conform. What followed was the grotesquely tragic spectacle of
philosophers struggling to prove the existence of an external world by
staring, with the Witch Doctor’s blind, inward stare, at the random twists of
their conceptions—then of perceptions—then of sensations.
When the medieval Witch Doctor had merely ordered men to doubt the validity of
their mind, the philosophers’ rebellion against him consisted of proclaiming
that they doubted whether man was conscious at all and whether anything existed
for him to be conscious of.