What is "sound change"

n. (context linguistics English) Any process of language change that affects pronunciation (phonetic change) or sound system structures (phonological change), manifested as a replacement of one speech sound (or, more generally, one phonetic feature) by another, as the complete loss of the affected sound, or by the introduction of a new sound in a place where there previously was none.

Sound change includes any processes of language change that affect pronunciation (phonetic change) or sound system structures ( phonological change). Sound change can consist of the replacement of one speech sound (or, more generally, one phonetic feature value) by another, the complete loss of the affected sound, or even the introduction of a new sound in a place where there had been none. Sound changes can be environmentally conditioned, meaning that the change only occurs in a defined sound environment, whereas in other environments the same speech sound is not affected by the change. The term "sound change" refers to diachronic changes—that is, irreversible changes in a language's sound system over time; " alternation", on the other hand, refers to changes that happen synchronically (i.e. within the language of an individual speaker, depending on the neighboring sounds) and which do not change the language's underlying system (for example, the -s in the English plural can be pronounced differently depending on what sound it follows; this is a form of alternation, rather than sound change). However, since "sound change" can refer to the historical introduction of an alternation (such as post-vocalic /k/ in Tuscan—once [k], but now [h])—the label is inherently imprecise and often must be clarified as referring to phonetic change or restructuring.

Research on sound change is usually conducted on the working assumption that it is regular, which means that it is expected to apply mechanically whenever its structural conditions are met, irrespective of any nonphonological factors (such as the meaning of the words affected). However, apparent exceptions to regular change can occur—due to dialect borrowing, grammatical analogy, or other causes, known and unknown—and some changes are described as "sporadic", meaning that they affect only one particular word or a few words, without any apparent regularity.

The Neogrammarian linguists of the 19th century introduced the term "sound law" to refer to rules of regular change, perhaps in imitation of the laws of physics. and the term "law" is still used in referring to specific sound rules named after their authors, such as Grimm's Law, Grassmann's Law, etc.. Real-world sound changes often admit exceptions; nevertheless, the expectation of their regularity or "exceptionlessness" is of great heuristic value, since it allows historical linguists to define the notion of regular correspondence (see: comparative method).

Each sound change is limited in space and time. This means it functions within a limited area (within certain dialects) and during a limited period of time. For these (and other) reasons, the term "sound law" has been criticized for implying a universality that is unrealistic with regard to sound change.

Sound change that affects the phonological system, in the number or distribution of its phonemes, is covered more fully at phonological change.