ut because both
sides, thought and extension, are only expressions of one and the same
fundamental substance, they correspond exactly to one another. The best
illustration of this is Fechner's simile of the curved line. It is concave
on one side, convex on the other, and thus entirely different on the two
sides. But at every point the concavity corresponds exactly to the
convexity. And this is possible because the two are the inner and the
outer aspects of the same line.

Others, again, go back to the fundamental ideas of critical idealism, and
declare the whole extended world accessible to the senses and the
mechanical-physical nexus of cause and phenomena, to be simply the form of
appearance in which the fundamentally spiritual existence presents itself
to our senses. Body, movement, physiological processes, are all nothing
more than the will, to speak with Fichte and Schopenhauer, or the idea, or
the spirit itself, which appears thus to sensory beings. Other theories,
some of them new, are also put forward.

No Parallelism.

For a long time it seemed as if the theory of parallelism was to gain
general acceptance. One might write a whole history of the gradually
increasing criticisms of, and reactions from the academic theories which
had become almost canonical. But we may here confine ourselves to the most
general of the objections to the parallelistic theory. They apply to the
general idea of parallelism itself, and affect the different standpoints
of the parallelists in different degrees. The theory in no way corresponds
to what we find in ourselves from direct experience. It is only with the
greatest difficulty that we can convince ourselves that our arm moves only
when and not because we will. The consciousness of being, through the
will, the actual cause of our own bodily movements is so energetic and
direct and certain, that it maintains its sway in spite of all objections,
and confuses the argument even of the parallelists themselves. Usually
after they have laid the foundations of a purely parallelistic theory,
they abandon it again as quickly as possible, and revert to the
expressions and images of ordinary thought. Indeed we have no clearer and
more certain example of causality in general than in our own capacity for
controlling changes in our own bodies. Further, a very fatal addition and
burdensome accessory of the parallelistic theory is involved in the two
corollaries it has above and beneath