Our whole theory of government and our laws of business and every-day
life are founded on the belief that men are the same to-day as
they were yesterday, and that they will be the same to-morrow. The
whole science of psychology is based on the observed and recorded
actions of the human organism under the influence of certain external
stimuli or forces, and starts from the assumption that this organism
has definite and permanent characteristics. If this is not so--if
the behavior of men in the past has not been governed by actual
laws which will also govern their behavior in the future--then
our laws of government are built on error, and the teachings of
psychology are foolish.

This does not mean that any man will necessarily act in the same
way to-morrow as he did yesterday, when subjected to the influence
of the same threat, inducement, or temptation; because, without
grappling the thorny question of free will, we realize that a man's
action is never the result of only one stimulus and motive, but
is the resultant of many; and we have no reason to expect that
he will act in the same way when subjected to the same stimulus,
unless we know that the internal and external conditions pertaining
to him are also the same. Furthermore, even if we cannot predict what
a certain individual will do, when exposed to a certain external
influence, because of some differences in his mental and physical
condition, on one occasion in comparison with another, yet when we
consider large groups of men, we know that individual peculiarities,
permanent and temporary, balance each other in great measure; that
the average condition of a group of men is less changeable than
that of one man, and that the degree of permanency of condition
increases with the number of men in the group. From this we may