Language change

Language change is the process of alteration in the features of a single language, or of languages in general, over time. It is studied in several subfields of linguistics: historical linguistics, sociolinguistics, and evolutionary linguistics. Traditional theories of historical linguistics identify three main types of change: systematic change in the pronunciation of phonemes, or sound change; borrowing, in which features of a language or dialect are introduced or altered as a result of influence from another language or dialect; and analogical change, in which the shape or grammatical behavior of a word is altered to more closely resemble that of another word. Research on language change generally assumes the uniformitarian principle—the presumption that language changes in the past took place according to the same general principles as language changes visible in the present.

Language change usually does not occur suddenly, but rather takes place via an extended period of variation, during which new and old linguistic features coexist. All living languages are continually undergoing change. Some commentators use derogatory labels such as "corruption" to suggest that language change constitutes a degradation in the quality of a language, especially when the change originates from human error or is a prescriptively discouraged usage. Modern linguistics rejects this concept, since from a scientific point of view such innovations cannot be judged in terms of good or bad. John Lyons notes that "any standard of evaluation applied to language-change must be based upon a recognition of the various functions a language 'is called upon' to fulfil in the society which uses it".

Over enough time, changes in a language can accumulate to such an extent that it is no longer recognizable as the same language. For instance, modern English is the result of centuries of language change applying to Old English, even though modern English is extremely divergent from Old English in grammar, vocabulary, and pronunciation. The two may be thought of as distinct languages, but Modern English is a "descendant" of its "ancestor" Old English. When multiple languages are all descended from the same ancestor language, as the Romance languages are from Vulgar Latin, they are said to form a language family and be "genetically" related.

According to Guy Deutscher, the tricky question is "Why are changes not brought up short and stopped in their tracks? At first sight, there seem to be all the reasons in the world why society should never let the changes through." He sees the reason for tolerating change in the fact that we already are used to "synchronic variation", to the extent that we are hardly aware of it. For example, when we hear the word "wicked", we automatically interpret it as either "evil" or "wonderful", depending on whether it is uttered by an elderly lady or a teenager. Deutscher speculates that "[i]n a hundred years' time, when the original meaning of 'wicked' has all but been forgotten, people may wonder how it was ever possible for a word meaning 'evil' to change its sense to 'wonderful' so quickly."

Sound change—i.e., change in the pronunciation of phonemes—can lead to phonological change (i.e., change in the relationships between phonemes within the structure of a language). For instance, if the pronunciation of one phoneme changes to become identical to that of another phoneme, the two original phonemes can merge into a single phoneme, reducing the total number of phonemes the language contains.

Determining the exact course of sound change in historical languages can pose difficulties, since the technology of sound recording dates only from the 19th century, and thus sound changes before that time must be inferred from written texts. The orthographical practices of historical writers provide the main (indirect) evidence of how language sounds have changed over the centuries. Poetic devices such as rhyme and rhythm can also provide clues to earlier phonetic and phonological patterns.

A principal axiom of historical linguistics, established by the linguists of the Neogrammarian school of thought in the 19th century, is that sound change is said to be "regular"—i.e., a given sound change simultaneously affects all words in which the relevant set of phonemes appears, rather than each word's pronunciation changing independently of each other. The degree to which the Neogrammarian hypothesis is an accurate description of how sound change takes place, rather than a useful approximation, is controversial; but it has proven extremely valuable to historical linguistics as a heuristic, and enabled the development of methodologies of comparative reconstruction and internal reconstruction that allow linguists to extrapolate backwards from known languages to the properties of earlier, unattested languages and hypothesize sound changes that may have taken place in them.

The study of lexical changes forms the diachronic portion of the science of onomasiology.