rable part in the causes of war--combat
as apart from practical motives and the complex moods into which, in
its modern form, it enters. Some writers appear to be deceived because
they assume that war is itself primitive, and do not see that in spite
of its conventions and its old forms, it is not far behind
civilization, not because civilization has made no progress, or is so
insecure, but because war, chaos though it be, in some respects
contains all our modern feelings. Kerr says that war is due to a
superfluity of animal force that must vent itself, but such
explanations of war seem certainly to be very far from the truth. That
theory is far from being adequate as an explanation of play. It is
much less so as an explanation of war. The other theory of play that
is most prevalent and which is offered as a theory of war--that play
and war are reversions to primitive instincts, is also insufficient.
War is neither an overflow of energy nor a reversion to primitive
states. Rather it is caused by and involves all the present and active
motives of man and all his essential human qualities.

_Social Instincts_

Whatever the specific causes of war may be, war is of course possible
only because there exists a mechanism or instinct or feeling, because
of which great groups of people act as a unit in the common interests
of all. We usually speak of this collective action as the result of
_social instincts_ or a general _social instinct_. It is the place of
this "instinct" in the causes and moods of war that we must consider.
War is a social phenomenon: it is a movement directed toward an
object, but the force that drives the movement is of course social.

Several writers, among them MacCurdy (37), Murray (90), and Trotter
(82), have dealt with this social aspect of war, and have interpreted
war as a herd reaction. All these theories are simple. Trotter
maintains that in man there are four instincts and no more:
self-preservative, reproductive nutritional, and herd instincts. The
peculiarity of the herd instinct is that it does not itself have
definite motor expression, but serves to intensify and direct the
other instincts. This herd instinct is a tendency, so to speak, which
can confer instinctive sanction upon any other part of the field of
action or belief. The herd instinct, for example, gives instinctive
quality to the social organization and social proclivities of three
different types of society, which appear as na