The “wave” concept is integral to Saussure’s model of geographical
linguistics—it describes the gradient manner in which dialects develop.
Linguistic waves, according to Saussure, are influenced by two opposed forces:
parochialism, which is the basic tendency of a population to preserve its
language’s traditions; and intercourse, in which communication between people
of different areas necessitates the need for cross-language compromise and
standardization. Intercourse can prevent dialectical fragmentation by
suppressing linguistic innovations; it can also propagate innovations
throughout an area encompassing different populations. Either way, the ultimate
effect of intercourse is unification of languages. Saussure remarks that there
is no barrier to intercourse where only gradual linguistic transitions occur.
Having outlined this monoglot model of linguistic diversity, which
illustrates that languages in any one area are undergoing perpetual and
nonuniform variation, Saussure turns to languages developing in two separate
areas.
In the case of segregated development, Saussure draws a distinction
between cases of contact and cases of isolation. In the latter, commonalities
may initially exist, but any new features developed will not be propagated
between the two languages. Nevertheless, differentiation will continue in each
area, leading to the formation of distinct linguistic branches within a
particular family.
The relations characterizing languages in contact are in stark contrast
to the relations of languages in isolation. Here, commonalities and differences
continually propagate to one another—thus, even those languages that are not
part of the same family will manage to develop common features.