as to do with the
main laws and principles that hold in all these special fields.

Psychology as Related to Other Sciences

A good definition of our science would distinguish it from other
sciences, especially from those neighboring sciences with which it is
in closest contact.

Psychology and sociology.

There is no difficulty in framing a good logical distinction here.
Sociology studies the activities of a group of people taken as a
whole, while psychology studies the activities of the individuals.
Both might be interested in the same social act, such as an election,
but sociology would consider this event as a unit, whereas psychology
would break it up into the acts of the several voters. The distinction
is clear enough theoretically, but breaks down often in practice, as
sociology would like to know the motives that swayed individual
voters, while psychology on its side is interested to know what
decision was reached by the majority. All the social sciences,
including economics and politics, have a psychological side, since
they evidently are concerned to know the causes that govern human
conduct. Social psychology studies the individual in his social
relations.

Psychology and biology.

Biology, being the science of living creatures, includes psychology,
which studies these creatures on the mental side. The science of life
includes the science of mental life. We may call psychology a part of
biology, or we may call it one of the biological sciences. It has very
close contact with several other branches of biology. Animal
psychology overlaps that part of zoology which studies the behavior of
animals. Genetic psychology, as it is sometimes called, i.e., the
study of mental heredity. {6} and development, dovetails with the
general biological science of genetics, so that we find biologists
gathering data on the heredity of feeble-mindedness or of musical
ability, while psychologists discuss the general theory of heredity.

Psychology and physiology.

That one of all the sciences that has the closest contacts with
psychology is human and animal physiology. Broadly defined, physiology
is that part of biology that studies functions or activities; and, so
defined, it includes psychology as part of itself. In practice,
psychology devotes itself to desire, thought, memory, and such "mental
functions", while physiology concentrates its effort upon "bodily
functions" like digestion and circulation. But this