The discrepancy between these two accounts was pointed out relatively early by Richard Aaron in his standard study, John Locke
( 3d ed., Oxford: Clarendon Press, 1971). Aaron explains the discrepancy by the supposition that "Locke himself, however, can see that this explanation [i.e., the first] is inadequate and tries again" (p. 108
We then get a summary of Locke's theory of sensation: "In the world of nature are certain physical objects, composed of a very great number of corpuscles. These affect our
sense-organs by emitting effluences or species which strike the sense-organs. This affection is then carried on to the brain, which in turn affects the mind. The consequence is
the idea in the mind" (ibid.
). Aaron concludes that Locke's theory is based on three
crucial unproved assumptions: "first, that such physical objects exist, that is, he
[ Locke] assumes a realism; secondly, that the brain being affected affects the mind, that
is, an interactionist theory of the mind-body relation; thirdly, that perception is
brought about causally by the action of physical objects on the mind through the
brain" (p. 109
In fact, nothing indicates that Locke makes either the second or third assumption.
Clearly, both assumptions presuppose that the senses convey a sensation to the brain,
which then affects the mind so as to produce a perception. Yet nowhere in the text is
there any mention of brain-mind interaction. Instead, we are simply told the senses
"convey into the mind what produces there those Perceptions." If we take this literally,
it suggests sensation is conveyed not merely to the brain but into the mind itself. As a
result, Locke does not need to assume any kind of brain-mind interaction. By having
sensation conveyed directly into the mind itself, he tacitly manages to avoid the problems of mind-body interaction.
Nevertheless, such a strategy leads to difficulties of another kind. The notion that
sensations are conveyed into the mind implies its capacity to contain these. But given
their physical quality, how can they be contained in something purely mental like the
mind? If we define sensation (as Locke does) in terms of a movement of animal spirits,