lness; my contents of consciousness are as such not in space;
their elements cannot pass through any space movements like the atoms of
the physicist. Instead of it, the psychical atoms, the sensations, have
different qualities, are blue and green, and cold and warm, and sweet
and sour, and toothache and headache. The changes which go on in such a
system are thus not changes of position and movements, but changes in
kind and strength and vividness and fusion; and exactly such changes are
the processes which the psychologist wants to explain. He wants to make
us understand why this idea grows up and the other fades away, why this
impression stands out with clearness as an attended object while the
other lacks vividness and disappears, why this volition grows out of
that emotion, why this feeling leads to this imaginative thought.

The first step towards such explanation is, of course, in psychology, as
in all other sciences, the careful observation of regularities. It
quickly leads us to formulate some general laws. Psychology has known,
for instance, for two thousand years, that if we have perceived two
things together, and later we see the one again, the new perception
brings us a memory image of the other thing. If we saw a man's face and
heard at the same time his name, seeing his face may later awaken in us
the memory of his name, or the hearing of his name may later awaken in
us a reproduced memory image of his face. On such a basis, for instance,
we formulate some general laws of association of ideas, and as soon as
we have such laws laid down, we consider the appearance of such a memory
image by association as sufficiently explained. We feel that it gives us
sufficient basis to predict that in the future this idea will stir up in
us the other idea. Psychology has formulated plenty of such general
statements, and they serve well for a first orientation.

Yet can this ever be considered as a last word of scientific explanation
of psychical facts? Can psychology really in this way reach an ideal
similar to that of scientific astronomy or chemistry? Would the
scientist of nature ever be satisfied with this kind of explanation,
which is nothing but generalization of certain sequences? Does not the
explanation of the naturalist contain an entirely different element? He
does not merely want to say that this effect has sometimes been observed
and that there is thus probability that it will come again, when similar
causes