The will, as we have elsewhere said, is a modification of the brain, by
which it is disposed to action or prepared to give play to the organs.
This will is necessarily determined by the qualities, good or bad,
agreeable or painful, of the object or the motive that acts upon his
senses; or of which the idea remains with him, and is resuscitated by
his memory. In consequence, he acts necessarily; his action is the
result of the impulse he receives either from the motive, from the
object, or from the idea, which has modified his brain, or disposed his
will. When he does not act according to this impulse, it is because
there comes some new cause, some new motive, some new idea, which
modifies his brain in a different manner, gives him a new impulse,
determines his will in another way; by which the action of the former
impulse is suspended: thus, the sight of an agreeable object, or its
idea, determines his will to set him in action to procure it; but if a
new object or a new idea more powerfully attracts him, it gives a new
direction to his will, annihilates the effect of the former, and
prevents the action by which it was to be procured. This is the mode in
which reflection, experience, reason, necessarily arrests or suspends
the action of man's will; without this, he would, of necessity, have
followed the anterior impulse which carried him towards a then desirable
object. In all this he always acts according to necessary laws, from
which he has no means of emancipating himself.

If, when tormented with violent thirst, he figures to himself an idea,
or really perceives a fountain, whose limpid streams might cool his
feverish habit, is he sufficient master of himself to desire or not to
desire the object competent to satisfy so lively a want? It will no
doubt be conceded, that it is impossible he should not be desirous to
satisfy it; but it will be said,--If at this moment it is announced to
him, the water he so ardently desires is poisoned, he will,