Psychological crowds, then, are susceptible of classification;
and when we come to occupy ourselves with this matter, we shall
see that a heterogeneous crowd--that is, a crowd composed of
dissimilar elements--presents certain characteristics in common
with homogeneous crowds--that is, with crowds composed of
elements more or less akin (sects, castes, and classes)--and side
by side with these common characteristics particularities which
permit of the two kinds of crowds being differentiated.

But before occupying ourselves with the different categories of
crowds, we must first of all examine the characteristics common
to them all. We shall set to work like the naturalist, who
begins by describing the general characteristics common to all
the members of a family before concerning himself with the
particular characteristics which allow the differentiation of the
genera and species that the family includes.

It is not easy to describe the mind of crowds with exactness,
because its organisation varies not only according to race and
composition, but also according to the nature and intensity of
the exciting causes to which crowds are subjected. The same
difficulty, however, presents itself in the psychological study
of an individual. It is only in novels that individuals are
found to traverse their whole life with an unvarying character.
It is only the uniformity of the environment that creates the
apparent uniformity of characters. I have shown elsewhere that
all mental constitutions contain possibilities of character which
may be manifested in consequence of a sudden change of
environment. This explains how it was that among the most savage
members of the French Convention were to be found inoffensive