prings from a preconceived opinion on the
government of the world. In all the sciences which deal with an
evolution we find individual facts which serve as starting-points for
series of vast transformations. A drove of horses brought by the
Spanish has stocked the whole of South America. In a flood a branch of
a tree may dam a current and transform the aspect of a valley.

In human evolution we meet with great transformations which have no
intelligible cause beyond an individual accident.[198] In the sixteenth
century England changed its religion three times on the death of a
sovereign (Henry VIII., Edward VI., Mary). Importance not to be measured
by the initial fact, but by the facts which resulted from it. We must
not, therefore, deny _a priori_ the action of individuals and discard
individual facts. We must examine whether a given individual was in a
position to make his influence strongly felt. There are two cases in
which we may assume that he was: (1) when his action served as an
example to a mass of men and created a tradition, a case frequent in
art, science, religion, and technical matters; (2) when he had power to
issue commands and direct the actions of a mass of men, as is the case
with the heads of a state, an army, or a church. The episodes in a man's
life may thus become important facts.

Accordingly, in the scheme of historical classification a place should
be assigned for persons and events.

VI. In every study of successive facts it is necessary to provide a
number of halting-places, to distinguish beginnings and ends, in order
that chronological divisions may be made in the enormous mass of facts.
These divisions are _periods_; the use of them is as old as history. We
need them, not only in general history, but in the special branches of
history as well, whenever we study an extent of time long enough for an
evolution to be sensible. It is by means of events that we fix their
limits.

In the special branches of history, after having decided what changes of
habits are to be considered as reaching deepest, we adopt them as
marking _dates_ in the evolution; we then inquire what event produced
them. The event which led to the formation or the change of a habit
becomes the beginning or the end of a period. Sometimes these boundary
events are of the same species as the facts whose evolution we are
studying--literary facts in the history of literature, political facts
in political history. But more oft