those relations which do
not assume an official form. This is one of the least advanced parts of
historical construction.

IV. The outcome of all this labour is a tabulated view of human life at
a given moment; it gives us the knowledge of a _state_ of society (in
German, _Zustand_). But history is not limited to the study of
simultaneous facts, taken in a state of rest, to what we may call the
_statics_ of society. It also studies the states of society at different
moments, and discovers the differences between these states. The habits
of men and the material conditions under which they live change from
epoch to epoch; even when they appear to be constant they do not remain
unaltered in every respect. There is therefore occasion to investigate
these changes; thus arises the study of successive facts.

Of these changes the most interesting for the work of historical
construction are those which tend in a common direction,[194] so that in
virtue of a series of gradual differentiations a usage or a state of
society is transformed into a different usage or state, or, to speak
without metaphor, cases where the men of a given period practise a habit
very different from that of their predecessors without any abrupt change
having taken place. This is _evolution_.

Evolution occurs in all human habits. In order to investigate it,
therefore, it is enough to turn once more to the series of questions
which we used in constructing a tabulated view of society. In respect of
each of the facts, conditions, usages, persons invested with authority,
official rules, the question is to be asked: What was the evolution of
this fact?

This study will involve several operations: (1) the determination of the
fact whose evolution is to be studied; (2) the fixing of the duration of
the time during which the evolution took place (the period should be so
chosen that while the transformation is obvious, there yet remains a
connecting link between the initial and the final condition); (3) the
establishing of the different stages of the evolution; (4) the
investigation of the means by which it was brought about.

V. A series, even a complete series, of all the states of all societies
and of all their evolutions would not be enough to exhaust the
subject-matter of history. There remains a number of unique facts which
we cannot pass over, because they explain the origin of certain states
of society, and form the starting-points of evolutions.