ability of
your will to raise your hand to your head or to cause your foot to make
one forward step?

If, nevertheless, you fancy you understand in what manner the will has
some of the bodily organs under its government, how, pray, do you
account for its not having all equally--the heart and liver as well as
the tongue and fingers? Without trying, you never would have discovered
that your bowels _will not_, any more than without trying you could have
known that your limbs _will_, ordinarily move in conformity with your
wishes. Neither, if one of your limbs were to be suddenly paralysed,
would you, until you tried, become aware that it would no longer move as
you wished. If there be, then, a power attached to the will, it is
plainly experience alone which apprises you of its existence; whereas
if you were independently conscious of it, you would know beforehand
precisely what it can and what it cannot effect, and would, moreover,
when you lost it, become instantly aware of your loss.

Again, and above all, does not anatomy teach us that when the mind wills
the movement of any bodily member, it 'is not the member itself which is
immediately moved, but certain intervening nerves, muscles, and animal
spirits, or possibly something still more minute and more unknown,'
through which the motion is successively propagated until it reach the
member? So that when the mind wills one event, a series of other events,
quite different and quite unthought of, take place instead; and it is
only by their means that the will's purpose is finally achieved. But how
can the mind be conscious, how can it form the remotest conception, of a
power which not only never does what the mind desires, but never does
aught of which the mind is cognisant?

And as we are thus utterly unable to perceive any power that the mind
has over the body, so are we equally unconscious of any power of the
mind over itself. We know as little of its internal nature and
constitution as we do of its mode of connection with the body. We know
by experience that at the bidding of the will ideas are continually
brought forward; but by what means they are brought forward we are
absolutely ignorant, as we are also of the reasons of the fluctuation of
mental activity, and why mental operations are more vigorous in health
than in sickness, before breakfast than after a heavy dinner or deep
carouse.

Such, on the issue immediately before us, is Hume's reasoning, to
which--