How could we
study the institutions or the evolution of France if we ignored the
conquest of Gaul by Caesar and the invasion of the Barbarians?

This necessity of studying unique facts has caused it to be said that
history cannot be a science, for every science has for its object that
which is general. History is here in the same situation as cosmography,
geology, the science of animal species: it is not the abstract knowledge
of the general relations between facts, it is a study which aims at
_explaining_ reality. Now, reality exists but once. There has been but a
single evolution of the world, of animal life, of humanity. In each of
these evolutions the successive facts have not been the product of
abstract laws, but of the concurrence, at each moment, of several
circumstances of different nature. This concurrence, sometimes called
chance, has produced a series of accidents which have determined the
particular course taken by evolution.[195] Evolution can only be
understood by the study of these accidents; history is here on the same
footing as geology or palaeontology.

Thus scientific history may go back to the accidents, or events, which
traditional history collected for literary reasons, because they struck
the imagination, and employ them for the study of evolution. We may thus
look for the facts which have influenced the evolution of each one of
the habits of humanity. Each event will be arranged under its date in
the evolution which it is supposed to have influenced. It will then
suffice to bring together the events of every kind, and to arrange them
in chronological and geographical order, to have a representation of
historical evolution as a whole.

Then, over and above the _special_ histories in which the facts are
arranged under purely abstract categories (art, religion, private life,
political institutions), we shall have constructed a concrete _general_
history, which will connect together the various special histories by
exhibiting the main stream of evolution which has dominated all the
special evolutions. None of the species of facts which we study apart
(religion, art, law, constitutions) forms a closed world within which
evolution takes place in obedience to a kind of internal impulse, as
specialists are prone to imagine. The evolution of a usage or of an
institution (language, religion, church, state) is only a metaphor; a
usage is an abstraction, abstractions do not evolve; it is only
_existence