Or, to state the same question in other terms: How is
psychology to be distinguished from physics? The answer provisionally
suggested at the outset of our inquiry was that psychology and physics
are distinguished by the nature of their causal laws, not by their
subject matter. At the same time we held that there is a certain subject
matter, namely images, to which only psychological causal laws are
applicable; this subject matter, therefore, we assigned exclusively to
psychology. But we found no way of defining images except through
their causation; in their intrinsic character they appeared to have no
universal mark by which they could be distinguished from sensations.
In this last lecture I propose to pass in review various suggested
methods of distinguishing mind from matter. I shall then briefly sketch
the nature of that fundamental science which I believe to be the true
metaphysic, in which mind and matter alike are seen to be constructed
out of a neutral stuff, whose causal laws have no such duality as that
of psychology, but form the basis upon which both physics and psychology
are built.
In search for the definition of "mental phenomena," let us begin with
"consciousness," which is often thought to be the essence of mind.
In the first lecture I gave various arguments against the view that
consciousness is fundamental, but I did not attempt to say what
consciousness is. We must find a definition of it, if we are to feel
secure in deciding that it is not fundamental. It is for the sake of the
proof that it is not fundamental that we must now endeavour to decide
what it is.
"Consciousness," by those who regard it as fundamental, is taken to be a
character diffused throughout our mental life, distinct from sensations
and images, memories, beliefs and desires, but present in all of
them.* Dr. Henry Head, in an article which I quoted in Lecture III,
distinguishing sensations from purely physiological occurrences, says:
"Sensation, in the strict sense of the term, demands the existence of
consciousness." This statement, at first sight, is one to which we feel
inclined to assent, but I believe we are mistaken if we do so. Sensation
is the sort of thing of which we MAY be conscious, but not a thing
of which we MUST be conscious. We have been led, in the course of our
inquiry, to admit unconscious beliefs and unconscious desires. There is,
so far as I can see, no class of mental or other occurrences of which we
are
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