usual sense.

The persistence of the group presents itself in the fact that, in spite
of the departure and the change of members, the group remains identical.
We say that it is the same state, the same association, the same army,
which now exists that existed so and so many decades or centuries ago;
this, although no single member of the original organization remains.
Here is one of the cases in which the temporal order of events presents
a marked analogy with the spatial order. Out of individuals existing
side by side, that is, apart from each other, a social unity is formed.
The inevitable separation which space places between men is nevertheless
overcome by the spiritual bond between them, so that there arises an
appearance of unified interexistence. In like manner the temporal
separation of individuals and of generations presents their union in our
conceptions as a coherent, uninterrupted whole. In the case of persons
spatially separated, this unity is effected by the reciprocity
maintained between them across the dividing distance. The unity of
complex being means nothing else than the cohesion of elements which is
produced by the reciprocal exercise of forces. In the case of temporally
separated persons, however, unity cannot be effected in this manner,
because reciprocity is lacking. The earlier may influence the later, but
the later cannot influence the earlier. Hence the persistence of the
social unity in spite of shifting membership presents a peculiar problem
which is not solved by explaining how the group came to exist at a given
moment.

a) _Continuity by continuance of locality._--The first and most
obvious element of the continuity of group unity is the continuance of
the locality, of the place and soil on which the group lives. The state,
still more the city, and also countless other associations, owe their
unity first of all to the territory which constitutes the abiding
substratum for all change of their contents. To be sure, the continuance
of the locality does not of itself alone mean the continuance of the
social unity, since, for instance, if the whole population of a state is
driven out or enslaved by a conquering group, we speak of a changed
civic group in spite of the continuance of the territory. Moreover, the
unity of whose character we are speaking is psychical, and it is this
psychical factor itself which makes the territorial substratum a unity.
After this has once taken place, however, th