vanced student, there are many books that deal exclusively
with this or that area of specialized interest. The present text
belongs within neither category. It aims simply to furnish
the beginning student with a solid foundation and a trust-
worthy framework for thinking about, or dealing with, human
nature as he finds it in his daily life. And, needless to say, it
should also prepare him for further, more intensive, study
in our field.

As you make your way, step by step, through this book, you
will notice certain outstanding characteristics of our approach.
These may well be mentioned in advance, as a preparation
for things to come. Our approach is biological, experimental,
and systematic. Biological, in that our basic principles will
often be drawn from the study of animal behavior, and will
be found to apply at various evolutionary levels; experi-
mental, in that these principles will be derived, not from
casual observation or untested opinion, but from laboratory
studies in which the important factors are isolated and varied
in such a manner as to permit scientific lawfulness to be dis-
covered; and systematic, in that the interrelation of experi-
mental facts will be one of our major concerns.

Tentatively we may define psychology as the science of the
behavior of organisms. Such a simple statement, however, is
both incomplete and misleading. Psychologists are not, as a
rule, equally interested in the behavior of all organisms.
Their attention is usually focussed primarily upon the human
being and a few of his near-relations in the animal kingdom
-- for example, the rat, the cat, the dog, the monkey, and the
chimpanzee. The comparative psychologist makes it his busi-
ness to examine differences and similarities of behavior
throughout the evolutionary scale. We, however, shall have
little interest in the activities of animals markedly different
from man, or in those infra-human activities which throw no
light on human conduct.

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