e simplest mental state
practically presents a most complex problem to scientific analysis. The
physician who really aims towards scientifically exact influence on the
human mind has reached the first step of his preparation as soon as he
understands that the content of consciousness is composed of hundreds
of thousands of elements. To treat the mind as if there were only a few
large pieces, one thing called memory and one thing called will and one
called emotion and so on, is as if a surgeon were to perform an
operation, knowing that there are arms and legs, but not knowing the
ramifications of the nerves and blood-vessels which his knife may
injure. Yet the description of these complex facts is only the beginning
of psychology. We saw that the real aim is their explanation.

III

MIND AND BRAIN

The central aim of the psychologist must be to explain the mental facts.
It is not sufficient to describe the procession of mental experiences in
us, we must understand the causes which determine that now this and now
that appears and disappears, and appears just in this combination of
elements. The astronomer is not satisfied with describing the stars, he
wants to explain their movements and to determine which movements are to
be expected. The psychologist, like the naturalist, aims towards
explanation, and it is this demand which forces him to look from the
psychical facts to the physical ones, from the mind to the brain. He is
under an illusion if he fancies that he can explain mental facts by
themselves. The purposive mind has its connection in itself, the causal
psychological mind demands for its connection the body. To understand
this necessity is the first step towards understanding the relation of
mind and brain.

The psychologist's problem of explanation is in one way entirely
different from that of the physicist. The physicist finds a world of an
unlimited number of atoms which are ultimately conceived as all alike,
but each one in a different place, and all the changes in the universe,
the movements of the stars, the waves of the ocean, are to be explained
by the causal connections of the movements of these atoms. The
psychologist, on the other hand, finds an endless manifoldness of
elements which are not in space, and which have no space form whatever.
My will is neither triangular nor oval; my emotion is neither shorter
than five feet nor longer; my memory image of a melody has no thickness
and no tal