relations of movement. The concept, therefore, is not founded
on substances themselves, but on their relations; while
the moving substance itself is the basis of the mechanistic
theory.

Both view-points are indispensable for the comprehension
of physical phenomena, and therefore both have attained
a general recognition. Meanwhile, because of the close
juxtaposition of the mechanistic and energic view-points,
a third conception has gradually grown up which is
mechanistic as well as energic; although, logically speaking,
the ascent from cause to effect, the progressive causal action,
cannot at the same time be the regressive choice of a means
to an end. ¹ It is not possible to conceive that the same
group of facts could be both causal and final in character,
for the one view excludes the other. There are the two
different standpoints, the one reversing the other; for the
principle of finality is the logical reverse of the principle
of causality. The concept of finality is not only logically
possible; it is also an indispensable, explanatory principle,
since no explanation of nature that is purely mechanistic
suffices, as the example of modern physics shows. If indeed
our concepts were exclusively those of substances moving

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