Dictionary-writers try to keep track of the changes in languages by recording (and, ideally, dating) the appearance in a language of new words, or of new usages for existing words. By the same token, they may tag some words eventually as "archaic" or "obsolete".
Semantic changes are shifts in the meanings of existing words. Basic types of semantic change include:
Can and Patton (2010) provide a quantitative analysis of twentieth-century Turkish literature using forty novels of forty authors. Using weighted least squares regression and a sliding window approach, they show that, as time passes, words, in terms of both tokens (in text) and types (in vocabulary), have become longer. They indicate that the increase in word lengths with time can be attributed to the government-initiated language "reform" of the 20th century. This reform aimed at replacing foreign words used in Turkish, especially Arabic- and Persian-based words (since they were in majority when the reform was initiated in early 1930s), with newly coined pure Turkish neologisms created by adding suffixes to Turkish word stems (Lewis, 1999).
Altintas, Can, and Patton (2007) introduce a systematic approach to language change quantification by studying unconsciously-used language features in time-separated parallel translations. For this purpose, they use objective style markers such as vocabulary richness and lengths of words, word stems and suffixes, and employ statistical methods to measure their changes over time.
Languages perceived to be "higher status" stabilise or spread at the expense of other languages perceived by their own speakers to be "lower-status".