Definition and Examples of Sound Change in English

In historical linguistics and phonology, sound change has been traditionally defined as "any appearance of a new phenomenon in the phonetic/phonological structure of a language" (Roger Lass in Phonology: An Introduction to Basic Concepts, 1984). More simply, sound change might be described as any particular change in the sound system of a language over a period of time.

"The drama of linguistic change," said English lexicographer and philologist Henry C. Wyld, "is enacted not in manuscripts or in inscriptions, but in the mouths and minds of men" (A Short History of English, 1927). 

There are many types of sound change, including the following:

• Aphesis and Apocope
• Assimilation 
• Dissimilation and Haplology
• Lexical Diffusion
• Metanalysis
• Metathesis
• Principle of Least Effort
• Prothesis
• Syncope

See Examples and Observations below. Also, see:

• The Great Vowel Shift
• Grimm's Law
• Isogloss
• Language Change
• Mutation
• Phonology
• Pronunciation
• Word Boundaries

Examples and Observations

• "An understanding of sound change is truly important for historical linguistics in general, and this needs to be stressed—it plays an extremely important role in the comparative method and hence also in linguistic reconstruction, in internal reconstruction, in detecting loanwords, and in determining whether languages are related to one another."
  (Lyle Campbell, Historical Linguistics: An Introduction, 2nd ed. MIT Press, 2004)
• Pronunciation of Schwa
  "There is a growing body of evidence that frequently used words quite often get affected early—an observation first made in the 19th century. . . .
  "Consider the words adultery, century, cursory, delivery, desultory, elementary, every, factory, nursery, slavery. If possible, write them down on a piece of paper and ask several friends to read them out loud. Better still, get people to read sentences which include the words. For example: A cursory glance at the newspaper suggests that adultery is on the increase in this century. If you think slavery has been abolished, go and look at the factory at the end of our road. Every mother will tell you that nursery schools are a mixed blessing. Make a careful note of how the crucial words are pronounced, and see if your results agree with those of a linguist who carried out an investigation of this type.
  "The investigator noted that, according to the dictionary, all words which are spelt with -ary, -ery, -ory or -ury are pronounced somewhat as if they rhymed with furry. The vowel preceding r is a so-called schwa, a short indeterminate sound written phonetically as [ə], and sometimes represented orthographically as er (British English) or uh (American English). In practice the schwa was not always pronounced. It was usually omitted in common words such as ev(e)ry, fact(o)ry, nurs(e)ry, which were pronounced as if they were spelt evry, factry, nursry with two syllables only. In slightly less common words, such as delivery, there was fluctuation. Some people inserted a schwa, others omitted it. A schwa was retained in the least common words, such as desultory, cursory."
  (Jean Aitchison, Language Change: Progress or Decay? 3rd ed. Cambridge Univ. Press, 2001)
• Theories of Sound Change
  "Various theories of sound change, some of them proposed a century ago or earlier were current in the [19]70s. There was a longstanding traditional view about sound change being due to speakers modifying their pronunciation either to make it easier—to expend less effort—or to make speech clearer for the sake of the listener. Another one was espoused by Halle (1962) that language change, including sound change, served to improve grammar by making it more cognitively simple to compute. Postal (1968) suggested it was due to speakers' desire for novelty, i.e., sounds change for the same reason that hemlines and haircuts change. Lightner (1970) claimed it was to avoid homophony--despite the abundant counter-examples that show homophony as the result of sound change. These are all teleological accounts, that is to say, they assume that the changes are purposeful, i.e., that they [are] motivated by a goal of some sort . . .."
  (John Ohala, "The Listener As a Source of Sound Change: An Update." The Initiation of Sound Change: Perception, Production, and Social Factors, ed. by Maria-Josep Solé and Daniel Recasens. John Benjamins, 2012)
• The Neogrammarian Regularity Hypothesis
  "In the 1870s a group of linguists now generally referred to as the Neogrammarians created a lot of attention, controversy, and excitement with the claim that unlike all other linguistic change, sound change is regular and operates without exceptions.
  "This Neogrammarian or regularity hypothesis led to a great deal of valuable and interesting research. However, as can be expected, such a strong claim did not remain without a good deal of often quite vociferous opposition. . . .
  "[I]t is important to note that the neogrammarian regularity hypothesis has proved to be enormously fruitful, no matter how accurate it may be in fact. For it forces the linguist to look for explanations of apparent irregularity, either by establishing a non-phonetic source or through a better formulation of a given sound change. Either way we learn more about the history of a given language and about the nature of linguistic change than if we subscribe to a view that does not expect regularity in sound change."
  (Hans Henrich Hock, Principles of Historical Linguistics, 2nd ed. Walter de Gruyter, 1991)