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PHYSIOLOGY AND PATHOLOGY. 239
as an external stimulus, whose action first of all causes
an image to arise in the brain, through the medium of
which the will carries out the effect proper an outward
action of the body. Now, in the human species however,
the place of such an image as this may be taken by a
conception drawn from former images of this kind by
dropping their differences, which conception consequently
is no longer perceptible, but merely denoted and fixed by
words. As the action of motives accordingly does not
depend upon contact, they can try their power on the will
a certain
against each other : in other words, they permit
choice which, in animals, is limited to the narrow sphere
of that which has perceptible existence for them ; whereas,
in man, its range comprises the vast extent of all that is
thinkable: that is, of his conceptions. Accordingly we
designate as voluntary
those movements which are occa
sioned, not by causes in the narrowest sense of the word,
as in inorganic bodies, nor even by mere stimuli, as in
plants, but by
1
motives. These motives however pre
suppose an intellect as their mediator, through which
causality here acts, without prejudice to its entire neces
sity in all other respects. Physiologically, the diffe
rence between stimulus and motive admits also of the
following definition. The stimulus provokes immediate
reaction, which proceeds from the very part on which
the stimulus has acted ; whereas the motive is a stimulus
that has to go a roundabout way through the brain,
where its action first causes an image to arise, which
then, but not till then, provokes the consequent reaction,
which is now called an act of volition, and voluntary. The
distinction between voluntary and involuntary movement
does not therefore concern what is essential and primary
1
I have shown the difference between cause in its narrowest sense,
stimulus, and motive, at length in my
p. 29 et scq.
"
Grund-probleme der Ethik .*