are given. No, the physicist wants to understand those
connections of cause and effect as necessary ones. He tries to find
sequences which cannot be otherwise because they cannot be thought in
any other way. Therefore he is not satisfied with complex regularities,
but analyzes them until he can bring them down to simple physical
connections, and these physical connections finally to mechanical
processes, which realize for us logical necessities. That matter lasts
and cannot disappear is such a presupposition, which comes to us with
the necessity of logical thinking. We simply cannot think it otherwise.
And the whole idea of natural science is to conceive the physical
universe in such a way that all changes in the outer world can be
understood as the movements of its parts in accordance with such
necessary physical axioms. If we knew all the atoms of the present
status of the universe, and we knew every present movement of every
atom, we should be able to foresee the position of every atom in the
next moment and in the following moment and in all following moments,
and all that by the necessary continuation of the substance and its
energies. That alone is the background of all special physical inquiry,
and we rely on the special laws of physics and chemistry, because we
trust that this universe, as a whole, could be ultimately understood as
such a system of necessary changes in the positions of the lasting
atoms.

For the psychologist there is no hope of finding such necessity in the
mental processes. The point is not that psychology is to-day too far
removed from the fulfillment of such an ideal, the point is rather that
such an ideal would be meaningless for the psychologist. His materials,
the psychical contents of consciousness, are by their nature unfit to
enter into such necessary connections; they cannot do it because they
cannot last. The physical object, we saw, is the object which is common
property, which we all feel in common, which must thus exist for all
time. The things in nature may burn down or decay, but no atom of them
can ever disappear from the universe, each must enter into new and ever
new combinations and last through all changes. The psychical thing, on
the other hand, can exist only for the one immediate experience. Every
sensation which enters into my ideas or volitions or emotions is a new
creation of the instant which cannot last; each one flashes up and is
lost with the moment's experience.