laws of the evolution of peoples. Having shown that the
historic races--that is, the races formed by the hazards of
history--finally acquired psychological characteristics as stable
as their anatomical characteristics, I attempted to explain how a
people transforms its institutions, its languages, and its arts.
I explained in the same work why it was that individual
personalities, under the influence of sudden variations of
environment, might be entirely disaggregated.

But besides the fixed collectivities formed by the peoples, there
are mobile and transitory collectivities known as crowds. Now
these crowds or mobs, by the aid of which the great movements of
history are accomplished, have characteristics absolutely
different from those of the individuals who compose them. What
are these characteristics, and how are they evolved? This new
problem was examined in The Psychology of the Crowd.

Only after these studies did I begin to perceive certain
influences which had escaped me.

But this was not all. Among the most important factors of
history one was preponderant--the factor of beliefs. How are
these beliefs born, and are they really rational and voluntary,
as was long taught? Are they not rather unconscious and
independent of all reason? A difficult question, which I dealt
with in my last book, Opinions and Beliefs.

So long as psychology regards beliefs as voluntary and rational
they will remain inexplicable. Having proved that they are
usually irrational and always involuntary, I was able to propound