tinct is inherited tendency. The possibility of
acquiring habits is peculiarly a human characteristic. While inanimate
things have a definite nature, a definite way of reacting to forces
which act upon them, they have little, if any, possibility of varying
their way of acting. Water might be said to have habits. If one cools
water, it turns to ice. If we heat it, it turns to steam. But it
_invariably_ does this. We cannot teach it any different way of acting.
Under the same conditions it always does the same thing.

Plants are very much like inanimate things. Plants have definite ways of
acting. A vine turns around a support. A leaf turns its upper surface to
the light. But one cannot teach plants different ways of acting. The
lower forms of animals are somewhat like plants and inanimate objects.
But to a very slight extent they are variable and can form habits. Among
the higher animals, such as dogs and other domestic animals, there is a
greater possibility of forming habits. In man there are the greatest
possibilities of habit-formation. In man the learned acts or habits are
many as compared to the unlearned acts or instincts; while among the
lower animals the opposite is the case--their instincts are many as
compared to their habits.

We may call this possibility of forming habits _plasticity_. Inanimate
objects such as iron, rocks, sulphur, oxygen, etc., have no plasticity.
Plants have very little possibility of forming habits. Lower animals
have somewhat more, and higher animals still more, while man has the
greatest possibility of forming habits. This great possibility of
forming habits is one of the main characteristics of man. Let us
illustrate the contrast between man and inanimate objects by an example.
If sulphur is put into a test tube and heated, it at first melts and
becomes quite thin like water. If it is heated still more, it becomes
thick and will not run out of the tube. It also becomes dark. Sulphur
_always_ does this when so treated. It cannot be taught to act
differently. Now the action of sulphur when heated is like the action of
a man when he turns to the right upon meeting a person in the street.
But the man has to acquire this habit, while the sulphur does not have
to learn its way of acting. Sulphur always acted in this way, while man
did not perform his act at first, but had to learn it by slow
repetition.

Everything in the world has its own peculiar nature, but man is unique
in that his n