le sound and a simple color sensation, or a simple taste and simple
smell sensation, can associate themselves through mere nervous
conditions of the brain, then there is nothing changed by going over to
more and more complex contents of consciousness. We may substitute a
whole landscape for a color patch or the memory of a book for a word,
but we do not reach by that a point where the physiological principle of
explanation, once admitted, begins to lose its value. Complexity is
certainly in good harmony with the bewildering manifoldness of those
thousands of millions of possible connections between the brain cells.

Every experience leaves the brain altered. The nerve fibers and the
cells have gone into new stages of disposition for certain excitements.
This disposition may be slowly lost. In that case the earlier experience
cannot be reproduced; we have forgotten it. But as long as the
disposition lasts--it is quite indifferent whether we conceive it more
in terms of chemical changes or physical variations, as processes in the
nerve cells or between the nerve cells--the physiological change alone
is responsible for the awakening of the memory idea under favoring
associative conditions. Of course, someone might reply: can we not fancy
that there remains on the psychical side also a disposition? Each idea
which we have experienced may have left a psychical trace which alone
may make it possible that the idea may come back to us again. But what
is really meant and what is gained by such a hypothesis?

First, do not let us forget that such a proposition could only have one
possible end in view, namely, the explanation of the reappearance of
memories. But when we discussed the basis of physiological psychology,
we convinced ourselves that mental facts as such are not causally
connected anyhow. Our real inner life has its internal connections,
connections of will and purpose, but as soon as we have taken that great
psychological step and look on inner life as merely psychological
objects, then the material is connected only through the underlying
physiological processes and we can never explain causally the appearance
of an idea through the preceding existence of another idea. We may
expect one after the other, but we have no insight into the mechanism
which makes the second follow after the first. Such insight into
necessary connection we find only on the physical side, and we saw that
just here lies the starting point for