eptions are psychic additions which must be explained on the causal
theory. This distinction is the product of an epoch in which physical
science has got ahead of medical pathology and of physiology.
Perceptions of push are just as much the outcome of transmission as are
perceptions of colour. When colour is perceived the nerves of the body
are excited in one way and transmit their message towards the brain, and
when push is perceived other nerves of the body are excited in another
way and transmit their message towards the brain. The message of the one
set is not the conveyance of colour, and the message of the other set is
not the conveyance of push. But in one case colour is perceived and in
the other case the push due to the object. If you snip certain nerves,
there is an end to the perception of colour; and if you snip certain
other nerves, there is an end to the perception of push. It would appear
therefore that any reasons which should remove colour from the reality
of nature should also operate to remove inertia.

Thus the attempted bifurcation of apparent nature into two parts of
which one part is both causal for its own appearance and for the
appearance of the other part, which is purely apparent, fails owing to
the failure to establish any fundamental distinction between our ways of
knowing about the two parts of nature as thus partitioned. I am not
denying that the feeling of muscular effort historically led to the
formulation of the concept of force. But this historical fact does not
warrant us in assigning a superior reality in nature to material inertia
over colour or sound. So far as reality is concerned all our
sense-perceptions are in the same boat, and must be treated on the same
principle. The evenness of treatment is exactly what this compromise
theory fails to achieve.

The bifurcation theory however dies hard. The reason is that there
really is a difficulty to be faced in relating within the same system of
entities the redness of the fire with the agitation of the molecules. In
another lecture I will give my own explanation of the origin of the
difficulty and of its solution.

Another favourite solution, the most attenuated form which the
bifurcation theory assumes, is to maintain that the molecules and ether
of science are purely conceptual. Thus there is but one nature, namely
apparent nature, and atoms and ether are merely names for logical terms
in conceptual formulae of calculation.

But