cessary a
study of heredity. We must find out how our thoughts, feelings,
sensations, and ideas are dependent upon a physical body and its organs.
A study of human actions shows that some actions are unlearned while
others are learned or acquired. The unlearned acts are known as
_instincts_ and the acquired acts are known as _habits_. Our psychology
must, therefore, treat of instincts and habits.

How man gets experience, and retains and organizes this experience must
be our problem in the chapters on sensations, ideas, memory, and
thinking. Individual differences in human capacity make necessary a
treatment of the different types and grades of intelligence, and the
compilation of tests for determining these differences. We must also
treat of the application of psychology to those fields where a knowledge
of human nature is necessary.

=Applied Psychology.= At the beginning of a subject it is legitimate to
inquire concerning the possibility of applying the principles studied to
practical uses, and it is very proper to make this inquiry concerning
psychology. Psychology, being the science of human nature, ought to be
of use in all fields where one needs to know the causes of human action.
And psychology is applicable in these fields to the extent that the
psychologist is able to work out the laws and principles of human
action.

In education, for example, we wish to influence children, and we must go
to psychology to learn about the nature of children and to find out how
we can influence them. Psychology is therefore the basis of the science
of education.

Since different kinds of work demand, in some cases, different kinds of
ability, the psychology of individual differences can be of service in
selecting people for special kinds of work. That is to say, we must have
sometime, if we do not now, a psychology of professions and vocations.
Psychological investigations of the reliability of human evidence make
the science of service in the court room. The study of the laws of
attention and interest give us the psychology of advertising. The study
of suggestion and abnormal states make psychology of use in medicine. It
may be said, therefore, that psychology, once abstract and unrelated to
any practical interests, will become the most useful of all sciences, as
it works out its problems and finds the laws of human behavior.

At present, the greatest service of psychology is to education. So true
is this that a departme