Locke’s Theory of Perception 249
which light is just at this moment beginning to be introduced
through the avenues of the sense-organs. Until the mind has
a body, no sensations can be caused in the mind, and until it
has sensory materials to work upon, it lacks the very founda-
tion of knowledge and experience. Locke’s whole Essay is
intended to drive this truth home, and to undermine the op-
posite well-known doctrine of “innate” ideas, according to
which knowledge blossoms forth from a source within the
mind itself, independent of sense-perception. The fountains
of knowledge are, according to Locke, in things themselves,
such that the mind’s point of contact with the whole of physi-
cal reality lies narrowly in the sense-organs of the body. For
the rationalists Descartes and the Cambridge Platonists, the
mind contacts ultimate reality only on an intellectual level
far above—indeed out of the reach of—sensation. Unless we
get the force of this distinction between a sensory and a
purely intellectual point of contact with reality, we shall miss
much of the peculiar significance of Locke. To know nature
truly, one must, if Locke is right, get down as it were into
his bodily senses and perceive out through them the nature of
things. He then contacts the real material world. Subse-
quently, he may turn inwards to reflect upon the operations
of his own mind, thus making acquaintance with mental sub-
stance. But even the most abstract and universal bit of
knowledge about the material world stands flat-footedly on
sensation.
Well, having supplied our body with a mind and the mind
with a body, sensation occurs, and the hitherto empty mind
begins to get a store of ideas. Let us see how these ideas are
produced and exactly what they are, on the level of percep-
tion.
Our animated organism sits up and looks at the marble we
used to perform a visual experiment. It sees a patch of white