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{{Short description|Process of language change that affects pronunciation or sound system structure}}
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{{Sound change}}
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In [[historical linguistics]], a '''sound change''' is a [[language change|change]] in the [[pronunciation]] of a language. A sound change can involve the replacement of one speech sound (or, more generally, one [[distinctive feature|phonetic feature]] value) by a different one (called '''phonetic change''') or a more general change to the speech sounds that exist (''[[phonological change]]''), such as the merger of two sounds or the creation of a new sound. A sound change can eliminate the affected sound, or a new sound can be added. Sound changes can be environmentally conditioned if the change occurs in only some [[phonetic environment|sound environments]], and not others.

The term "sound change" refers to [[historical linguistics|diachronic]] changes, which occur in a language's sound system. On the other hand, "[[alternation (linguistics)|alternation]]" refers to changes that happen [[synchronic analysis|synchronically]] (within the language of an individual speaker, depending on the neighbouring sounds) and do not change the language's [[underlying representation|underlying system]] (for example, the ''-s'' in the [[English plural]] can be pronounced differently depending on the preceding sound, as in ''bet''[s], ''bed''[z], which is a form of alternation, rather than sound change). Since "sound change" can refer to the historical introduction of an alternation (such as postvocalic /k/ in the [[Tuscan dialect]], which was once [k] as in ''di'' [k]''arlo'' 'of Carlo' but is now [h] ''di'' [h]''arlo'' and alternates with [k] in other positions: ''con'' [k]''arlo'' 'with Carlo'), that label is inherently imprecise and must often be clarified as referring to either phonemic change or restructuring.

Research on sound change is usually conducted under 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 non-phonological factors like the meaning of the words that are affected. Apparent exceptions to regular change can occur because of dialect borrowing, grammatical analogy, or other causes known and unknown, and some changes are described as "sporadic" and so they affect only one or a few particular 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,<ref>Sihler, p. 50</ref> and the term "law" is still used in referring to specific sound rules that are named after their authors like [[Grimm's law]], [[Grassmann's law]], [[:Category:Sound laws|etc.]] Real-world sound laws often admit exceptions, but the expectation of their regularity or absence of exceptions is of great [[heuristic]] value{{explain |date=August 2024 |reason=unclear why acknowledging exceptions makes sounds changes less understandable or would prevent the application of the comparative method}} by allowing historical linguists to define the notion of ''regular correspondence'' by the [[comparative method]].{{citation needed|date=August 2024}}

Each sound change is limited in space and time and so it functions in a limited area (within certain [[dialects]]) and for a limited period of time. For those and other reasons, the term "sound law" has been criticized for implying a universality that is unrealistic for sound change.<ref>"The French phoneticians and the Fino-Ugric linguists" are examples according to Anttila, p. 85.</ref>

A sound change that affects the phonological system or the number or the distribution of its [[phonemes]] is a [[phonological change]].

==Principles==

The following statements are used as heuristics in formulating sound changes as understood within the [[Neogrammarian]] model. However, for modern linguistics, they are not taken as inviolable rules but are seen as guidelines.

'''Sound change has no memory''': Sound change does not discriminate between the sources of a sound. If a previous sound change causes X,Y > Y (features X and Y merge as Y), a new one cannot affect only an original X.

'''Sound change ignores grammar''': A sound change can have only phonological constraints, like X > Z in [[stress (linguistics)|unstressed]] [[syllables]]. For example, it cannot affect only [[adjective]]s. The only exception is that a sound change may recognise word boundaries, even when they are unindicated by [[prosody (linguistics)|prosodic]] clues. Also, sound changes may be [[regularization (linguistics)|regularized]] in [[inflectional paradigm]]s (such as verbal inflection), when it is no longer [[phonology|phonological]] but [[morphology (linguistics)|morphological]] in nature.<ref>See Hill, Nathan W. (2014) '[http://eprints.soas.ac.uk/18595/ Grammatically conditioned sound change].' ''Language and Linguistics Compass,'' 8 (6). pp. 211-229.</ref>

'''Sound change is exceptionless''': If a sound change can happen at a place, it will affect all sounds that meet the criteria for change. Apparent exceptions are possible because of [[analogy]] and other regularization processes, another sound change, or an unrecognized conditioning factor. That is the traditional view expressed by the Neogrammarians. In the past decades, however, this has been challenged by the theory of [[lexical diffusion]], which argues that sound change need not necessarily affect all possible words. However, when a sound change is initiated, it often eventually expands to the whole [[lexicon]]. For example, the [[Spanish language|Spanish]] fronting of the [[Vulgar Latin]] [g] ([[voiced velar stop]]) before [i e ɛ] seems to have reached every possible word. By contrast, the voicing of word-initial Latin [k] to [g] occurred in ''colaphus'' > ''golpe'' and ''cattus'' > ''gato'' but not in ''canna'' > ''caña''.

'''Sound change is inevitable''': All languages vary from place to place and time to time, and neither writing nor media prevents that change.

==Formal notation==
{{See also|Phonological rule}}
A statement of the form

::{{code|A > B}}

is to be read as "Sound A changes into (or is replaced by, is reflected as, etc.) sound B". Therefore, A belongs to an older stage of the language in question, and B belongs to a more recent stage. The symbol ">" can be reversed, B < A, which also means that the (more recent) B derives from the (older) A":

::POc. *t > Rot. f

:means that "[[Proto-Oceanic language|Proto-Oceanic]] (POc.) *t is reflected as {{IPA|[f]}} in [[Rotuman language|Rotuman]] (Rot.)".

The two sides of such a statement indicate only the start and the end of the change, but additional intermediate stages may have occurred. The example above is actually a compressed account of a ''sequence'' of changes: *{{IPA|[t]}} first changed to {{IPA|[θ]}} (like the initial consonant of [[English language|English]] ''thin''), which has since yielded {{IPA|[f]}} and can be represented more fully:

:: t > {{IPA|θ}} > f

Unless a change operates unconditionally (in all environments), the context in which it applies must be specified:

::A > B /X__Y

:= "A changes to B when it is preceded by X and followed by Y."

For example:

::It. b > v /[vowel]__[vowel], which can be simplified to just
::It. b > v /V__V (in which the V stands for any vowel)

:= "Intervocalic [b] (inherited from [[Latin]]) became [v] in [[Italian language|Italian]]" (such as in ''caballum, dēbet'' > ''cavallo'' 'horse', ''deve'' 'owe (3rd pers. sing.)'

Here is a second example:

::PIr. [&minus;cont][&minus;voi] > [+cont] /__[C][+cont]

:= "A preconsonantal voiceless non-continuant (voiceless stop) changed into corresponding a voiceless continuant ([[fricative consonant|fricative]]) in [[Proto-Iranian]] (PIr.)" when it was immediately followed by a continuant consonant (a [[resonant consonant|resonant]] or a fricative): [[Proto-Indo-Iranian]] *''pra'' 'forth' > [[Avestan language|Avestan]] ''fra''; *''trayas'' "three" (masc. nom. pl.)> Av. ''θrayō''; *''čatwāras'' "four" (masc. nom. pl.) > Av. ''čaθwārō''; *''pśaws'' "of a cow" (nom. *''paśu'') > Av. ''fšāoš'' (nom. ''pasu''). The fricativization did not occur before stops and so *''sapta'' "seven" > Av. ''hapta''. (However, in the variety of [[Iranian languages|Iranian]] that led to [[Old Persian]], fricativization occurred in all clusters: Old Persian ''hafta'' "seven".)

The symbol "#" stands for a word boundary (initial or final) and so the notation "/__#" means "word-finally", and "/#__" means "word-initially":

::Gk. [stop] > ∅ /__#

:= "Word-final stops were deleted in [[Greek language|Greek]] (''Gk.'')".

That can be simplified to

::Gk. P > ∅ / __#

in which P stands for any [[plosive consonant|plosive]].

==Terms for changes in pronunciation==

In [[historical linguistics]], a number of traditional terms designate types of phonetic change, either by nature or result. A number of such types are often (or usually) sporadic, that is, more or less accidents that happen to a specific form. Others affect a whole phonological system. Sound changes that affect a whole phonological system are also classified according to how they affect the overall shape of the system; see ''[[phonological change]]''.

* [[Assimilation (linguistics)|Assimilation]]: One sound becomes more like another, or (much more rarely) two sounds become more like each other. Example: in Latin the prefix *''kom''- becomes ''con''- before an [[Apical consonant|apical stop]] ({{IPA|[t d]}}) or {{IPA|[n]}}: ''contactus'' "touched", ''condere'' "to found, establish", ''connūbium'' "legal marriage". The great majority of assimilations take place between contiguous segments,{{Citation needed|date= September 2012}} and the great majority involve the earlier sound becoming more like the later one (e.g. in ''connūbium,'' ''m- + n'' becomes ''-nn-'' rather than ''-mm-''). Assimilation between contiguous segments are ([[diachronics|diachronically]] speaking) exceptionless sound laws rather than sporadic, isolated changes.{{Citation needed|date=September 2012}}
* [[Dissimilation]]: The opposite of assimilation. One sound becomes less like another, or (much more rarely) two sounds become less like each other. Examples: Classical Latin ''quīnque'' {{IPA|/kʷiːnkʷe/}} "five" > Vulgar Latin *''kinkʷe'' (whence French ''cinq'', Italian ''cinque'', etc.); [[Old Spanish language|Old Spanish]] ''omne'' "man" > Spanish ''hombre''. The great majority of dissimilations involve segments that are {{em|not}} contiguous, but, as with assimilations, the great majority involve an earlier sound changing with reference to a later one. Dissimilation is usually a sporadic phenomenon, but [[Grassmann's Law]] (in Sanskrit and Greek) exemplifies a systematic dissimilation. If the change of a sequence of fricatives such that one becomes a stop is dissimilation, then such changes as [[Proto-Germanic language|Proto-Germanic]] *hs to {{IPA|/ks/}} (spelled ''x'') in English would count as a regular sound law: PGmc. *''sehs'' "six" > [[Old English]] ''siex'', etc.
* [[Metathesis (linguistics)|Metathesis]]: Two sounds switch places. Example: Old English ''th'''ri'''dda'' became Middle English ''th'''ir'''d''. Most such changes are sporadic, but occasionally a sound law is involved, as Romance *''tl'' > Spanish ''ld'', thus *''kapitlu, *titlu'' "chapter (of a cathedral)", "[[tittle]]" > Spanish ''cabildo, tilde''. Metathesis can take place between non-contiguous segments, as Greek ''amélgō'' "I milk" > Modern Greek ''armégō.''
* [[Lenition]]: "Weakening" of a consonant from one that takes more effort to pronounce (and more constriction in the vocal tract) to one that takes less, e.g. a [[stop consonant]] becoming an [[affricate]] or [[fricative]].
* [[Fortition]]: the opposite of lenition, "strengthening" a consonant, e.g. an [[approximant]] becoming an affricate or fricative.
* [[Vowel reduction|Reduction]]: Whereas the weakening of consonants is called ''lenition'', the weakening of vowels is called ''reduction''. For example, in most varieties of English, unstressed vowels often reduce to a [[schwa]], such as the two a's in ''arena''.
* [[Tonogenesis]]: Syllables come to have distinctive [[pitch contour]]s.
* [[Sandhi]]: Conditioned changes that take place at word-boundaries but not elsewhere. It can be [[morpheme]]-specific, as in the loss of the vowel in the enclitic forms of English ''is'' {{IPA|/ɪz/}}, with subsequent change of {{IPA|/z/}} to {{IPA|/s/}} adjacent to a voiceless consonant ''Frank's not here'' {{IPA|/ˈfræŋksnɒtˈhɪər/}}. Or a small class of elements, such as the assimilation of the {{IPA|/ð/}} of English ''the, this'' and ''that'' to a preceding {{IPA|/n/}} (including the {{IPA|/n/}} of ''and'' when the {{IPA|/d/}} is elided) or {{IPA|/l/}}: ''all the'' often {{IPA|/ɔːllə/}}, ''in the'' often {{IPA|/ɪnnə/}}, and so on. As in these examples, such features are rarely indicated in standard orthography. In a striking exception, Sanskrit orthography reflects a wide variety of such features; thus, ''tat'' "that" is written ''tat'','' tac'','' taj'','' tad'','' ''or ''tan'' depending on what the first sound of the next word is. These are all assimilations, but medial sequences do not assimilate the same way.
* [[Haplology]]: The loss of a syllable when an adjacent syllable is similar or (rarely) identical. Example: Old English ''Englaland'' became Modern English ''England'', or the common pronunciation of ''probably'' as {{IPA|[ˈprɒbli]}}. This change usually affects commonly used words. The word ''haplology'' itself is sometimes jokingly pronounced ''haplogy''.
* [[Elision]], [[Apheresis (linguistics)|aphaeresis]], [[Syncope (phonetics)|syncope]], and [[apocope]]: All are losses of sounds. Elision is the loss of unstressed sounds, aphaeresis the loss of initial sounds, syncope is the loss of medial sounds, and apocope is the loss of final sounds.
** Elision examples: in the southeastern United States, unstressed schwas tend to drop, so "American" is not {{IPA|/əˈmɛɹəkən/}} but {{IPA|/ˈmɚkən/}}. Standard English is ''possum'' < ''opossum''.
** Syncope examples: the Old French word for "state" is ''estat'', but the ''s'' disappeared, yielding ''état''. Similarly, the loss of {{IPA|/t/}} in English ''soften, hasten, castle'', etc.
** Apocope examples: the final -''e'' {{IPA|[ə]}} in Middle English words was pronounced, but is only retained in spelling as a [[silent E]]. In English {{IPA|/b/}} and {{IPA|/ɡ/}} were apocopated in final position after nasals: ''lamb, long'' {{IPA|/læm/, /lɒŋ ~ lɔːŋ/}}.
* [[Epenthesis]] (also known as anaptyxis): The introduction of a sound between two adjacent sounds. Examples: Latin ''humilis'' > English ''humble''; in Slavic an -l- intrudes between a labial and a following yod, as *''zemya'' "land" > Russian ''zemlya'' (земля). Most commonly, epenthesis is in the nature of a "transitional" consonant, but vowels may be epenthetic: non-standard English ''film'' in two syllables, ''athlete'' in three. Epenthesis can be regular, as when the Indo-European "tool" suffix *-''tlom'' everywhere becomes Latin -''culum'' (so ''speculum'' "mirror" < *''speḱtlom'', ''pōculum'' "drinking cup" < *''poH<sub>3</sub>-tlom''). Some scholars reserve the term ''epenthesis'' for "intrusive" vowels and use ''excrescence'' for intrusive consonants.
* [[Prothesis (linguistics)|Prothesis]]: The addition of a sound at the beginning of a word. Example: word-initial {{IPA|/s/}} + stop clusters in Latin gained a preceding {{IPA|/e/}} in Old Spanish and Old French; hence, the Spanish word for "state" is ''estado'', deriving from Latin ''status''.
* [[Nasalization]]: Vowels followed by nasal consonants can become nasalized. If the nasal consonant is lost but the vowel retains its nasalized pronunciation, nasalization becomes [[phoneme|phonemic]], that is, distinctive. Example: French "-in" words used to be pronounced {{IPA|[in]}}, but are now pronounced {{IPA|[ɛ̃]}}, and the {{IPA|[n]}} is no longer pronounced (except in cases of [[liaison (French)|liaison]]).

==Examples of specific sound changes in various languages==

* [[Ingvaeonic nasal spirant law|Anglo-Frisian nasal spirant law]]
* [[Canaanite shift]]
* [[Cot-caught merger]]
* [[Dahl's law]]
* [[Grassmann's law]]
* [[Great Vowel Shift]] (English)
* [[Grimm's law]]
* [[High German consonant shift]]
* [[Kluge's law]]
* [[Onbin]]
* [[Phonetic change "f → h" in Spanish]]
* [[Ruki sound law]]
* [[Slavic palatalization (disambiguation)|Slavic palatalization]]
* [[I-mutation|Umlaut]]
* [[Verner's law]]

==See also==
* [[Glossary of sound laws in the Indo-European languages]]

==Notes==
{{Reflist}}

==References==
* Anttila, Raimo (1989). ''Historical and Comparative Linguistics''. John Benjamins.
* Campbell, Lyle (2004). ''Historical Linguistics: An Introduction''. The MIT Press.
* Hale, Mark (2007). ''Historical Linguistics: Theory and Method''. Oxford, Blackwell
* Hock, Hans Henrich (1991). ''Principles of Historical Linguistics''. Mouton De Gruyter.
* McDorman, Richard E. (1999). ''Labial Instability in Sound Change''. Organizational Knowledge Press.
* Morley, Rebecca (2019). ''Sound Structure and Sound Change: A Modeling Approach''. Berlin: Language Science Press. {{ISBN|978-3-96110-191-7}}. {{doi|10.5281/zenodo.3264909}}. Open Access. http://langsci-press.org/catalog/book/251
* Sihler, Andrew L. (2000). ''Language History: An Introduction''. John Benjamins.
{{Historical linguistics}}
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[[Category:Historical linguistics]]
[[Category:Phonology]]
[[Category:Sound changes|*]]