  All living languages change over time. The causes for this are many, one
being the emergence and borrowing of new linguistic elements. Competition
between the new elements and older ones with a similar semantic or grammatical
function may lead to speakers preferring one of them, and leaving the other to
go out of use. We introduce a general method for quantifying competition
between linguistic elements in diachronic corpora which does not require
language-specific resources other than a sufficiently large corpus. This
approach is readily applicable to a wide range of languages and linguistic
subsystems. Here, we apply it to lexical data in five corpora differing in
language, type, genre, and time span. We find that changes in communicative
need are consistently predictive of lexical competition dynamics.
Near-synonymous words are more likely to directly compete if they belong to a
topic of conversation whose importance to language users is constant over time,
possibly leading to the extinction of one of the competing words. By contrast,
in topics which are increasing in importance for language users,
near-synonymous words tend not to compete directly and can coexist. This
suggests that, in addition to direct competition between words, language change
can be driven by competition between topics or semantic subspaces.
