152

CHAPTER IX. INDIVIDUAL DIFFERENCES 176

CHAPTER X. APPLIED PSYCHOLOGY 210

GLOSSARY 223

INDEX 227

THE SCIENCE OF HUMAN NATURE

CHAPTER I

INTRODUCTION

=Science.= Before attempting to define psychology, it will be helpful to
make some inquiry into the nature of science in general. Science is
knowledge; it is what we know. But mere knowledge is not science. For a
bit of knowledge to become a part of science, its relation to other bits
of knowledge must be found. In botany, for example, bits of knowledge
about plants do not make a science of botany. To have a science of
botany, we must not only know about leaves, roots, flowers, seeds, etc.,
but we must know the relations of these parts and of all the parts of a
plant to one another. In other words, in science, we must not only
_know_, we must not only have _knowledge_, but we must know the
significance of the knowledge, must know its _meaning_. This is only
another way of saying that we must have knowledge and know its relation
to other knowledge.

A scientist is one who has learned to organize his knowledge. The main
difference between a scientist and one who is not a scientist is that
the scientist sees the significance of facts, while the non-scientific
man sees facts as more or less unrelated things. As one comes to hunt
for causes and inquire into the significance of things, one becomes a
scientist. A thing or an event always points beyond itself to something
else. This something else is what goes before it or comes after it,--is
its cause or its effect. This causal relationship that exists between
events enables a scientist to prophesy. By carefully determining what
always precedes a certain event, a certain type of happening, a
scientist is able to predict the event. All that is necessary to be able
to predict an event is to have a clear knowledge of its true causes.
Whenever, beyond any doubt, these causes are found to be present, the
scientist knows the event will follow. Of course, all that he really
_knows_ is that such results have always followed similar causes in the
past. But he has come to have faith in the uniformity and regularity of
nature. The chemist does not find sulphur, or oxygen, or any other
element acting one w