of a
different kind from either reflex or voluntary movements, and more akin
to the movements of dead matter. We may define a movement of an animal's
body as "mechanical" when it proceeds as if only dead matter were
involved. For example, if you fall over a cliff, you move under the
influence of gravitation, and your centre of gravity describes just as
correct a parabola as if you were already dead. Mechanical movements
have not the characteristic of appropriateness, unless by accident, as
when a drunken man falls into a waterbutt and is sobered. But reflex
and voluntary movements are not ALWAYS appropriate, unless in some very
recondite sense. A moth flying into a lamp is not acting sensibly; no
more is a man who is in such a hurry to get his ticket that he cannot
remember the name of his destination. Appropriateness is a complicated
and merely approximate idea, and for the present we shall do well to
dismiss it from our thoughts.

As James states, there is no difference, from the point of view of
the outside observer, between voluntary and reflex movements. The
physiologist can discover that both depend upon the nervous system,
and he may find that the movements which we call voluntary depend upon
higher centres in the brain than those that are reflex. But he
cannot discover anything as to the presence or absence of "will" or
"consciousness," for these things can only be seen from within, if
at all. For the present, we wish to place ourselves resolutely in the
position of outside observers; we will therefore ignore the distinction
between voluntary and reflex movements. We will call the two together
"vital" movements. We may then distinguish "vital" from mechanical
movements by the fact that vital movements depend for their causation
upon the special properties of the nervous system, while mechanical
movements depend only upon the properties which animal bodies share with
matter in general.

There is need for some care if the distinction between mechanical and
vital movements is to be made precise. It is quite likely that, if we
knew more about animal bodies, we could deduce all their movements from
the laws of chemistry and physics. It is already fairly easy to see how
chemistry reduces to physics, i.e. how the differences between different
chemical elements can be accounted for by differences of physical
structure, the constituents of the structure being electrons which are
exactly alike in all kinds of matter. We