In historical linguistics, phonological change is any sound change that alters the distribution of phonemes in a language. In other words, a language develops a new system of oppositions among its phonemes. Old contrasts may disappear, new ones may emerge, or they may simply be rearranged. Sound change may be an impetus for changes in the phonological structures of a language (and likewise, phonological change may sway the process of sound change). One process of phonological change is rephonemicization, in which the distribution of phonemes changes by either addition of new phonemes or a reorganization of existing phonemes. Mergers and splits are types of rephonemicization and are discussed further below.
Types In a typological scheme first systematized by Henry M. Hoenigswald in 1965, a historical sound law can only affect a phonological system in one of three ways: Conditioned merger (which Hoenigswald calls "primary split"), in which some instances of phoneme A become an existing phoneme B; the number of phonemes does not change, only their distribution. Phonemic split (which Hoenigswald calls "secondary split"), in which some instances of A become a new phoneme B; this is phonemic differentiation in which the number of phonemes increases. Unconditioned merger, in which all instances of phonemes A and B become A; this is phonemic reduction, in which the number of phonemes decreases. This classification does not consider mere changes in pronunciation, that is, phonetic change, even chain shifts, in which neither the number nor the distribution of phonemes is affected.
Phonetic vs. phonological change Phonetic change can occur without any modification to the phoneme inventory or phonemic correspondences. This change is purely allophonic or subphonemic. This can entail one of two changes: either the phoneme turns into a new allophone—meaning the phonetic form changes—or the distribution of allophones of the phoneme changes.
For the most part, phonetic changes are examples of allophonic differentiation or assimilation; i.e., sounds in specific environments acquire new phonetic features or perhaps lose phonetic features they originally had. Some examples are these: the devoicing of the vowels and in certain environments in Japanese, the nasalization of vowels before nasals (common but not universal), and changes to the place of articulation of stops and nasals under the influence of adjacent vowels.
Phonetic change in this context refers to the lack of phonological restructuring, not a small degree of sound change. For example, chain shifts such as the Great Vowel Shift (in which nearly all of the vowels of the English language changed) or the allophonic differentiation of /s/, originally , into , do not qualify as phonological change as long as all of the phones remain in complementary distribution.
Many phonetic changes provide the raw ingredients for later phonemic innovations. In Proto-Italic, for example, intervocalic */s/ became *[z]. It was a phonetic change, merely a mild and superficial complication in the phonological system, but when *[z] merged with */r/, the effect on the phonological system was greater. (The example will be discussed below, under conditioned merger.)
Similarly, in the prehistory of Indo-Iranian, the velars */k/ and */g/ acquired distinctively palatal articulation before front vowels (*/e/, */i/, */ē/ */ī/), so that came to be pronounced and , but the phones and occurred only in that environment. However, when */e/, */o/, */a/ later fell together as Proto-Indo-Iranian */a/ (and */ē/ */ō/ */ā/ likewise fell together as */ā/), the result was that the allophonic palatal and velar stops now contrasted in identical environments: */ka/ and /ča/, /ga/ and /ǰa/, and so on. The difference became phonemic. (The "law of palatals" is an example of phonemic split.)
Sound changes generally operate for a limited period of time, and once established, new phonemic contrasts rarely remain tied to their ancestral environments. For example, Sanskrit acquired "new" /ki/ and /gi/ sequences via analogy and borrowing, and likewise /ču/, , /čm/, and similar novelties; and the reduction of the diphthong */ay/ to Sanskrit /ē/ had no effect at all on preceding velar stops.
Merger
Phonemic merger is a loss of distinction between phonemes. Occasionally, the term reduction refers to phonemic merger. It is not to be confused with the meaning of the word "reduction" in phonetics, such as vowel reduction, but phonetic changes may contribute to phonemic mergers. For example, in most North American English dialects, the vowel in the word lot and vowel in the word palm have become the same sound and thus undergone a merger. In most dialects of England, the words father and farther are pronounced the same due to a merger created by non-rhoticity or "R-dropping".
Conditioned merger Conditioned merger, or primary split, takes place when some, but not all, allophones of a phoneme, say A, merge with some other phoneme, B. The immediate results are these: there are the same number of contrasts as before. there are fewer words with A than before. there are more words with B than before. there is at least one environment in which A, for the time being, no longer occurs, called a gap in the distribution of the phoneme. if inflection or derivation results in A sometimes but not always being in the environment in which it has merged with B, an alternation in that environment between A and B may develop.
Example from Middle English
For a simple example, without alternation, early Middle English after stressed syllables followed by became : > mother, father, > weather. Since was already a structure-point in the language, the innovation resulted merely in more and less and a gap in the distribution of (though not a very conspicuous one). Note 1: thanks to borrowing, from dialects as well as other languages, the original distribution has been disturbed: rudder, adder in Standard English (but forms with are attested in nonstandard dialects). Note 2: one who knows German can figure out which cases of English were originally and which changed from . Original corresponds to in German, and original corresponds to . Thus, leather = German , brother = , whether = , wether = Widder, pointing to original in English; weather = German , father = , mother = pointing to original . Note 3: alternation between and would have been a theoretical possibility in English, as in sets like hard, harder; ride, rider, but any such details have been erased by the commonplace diachronic process called morphological leveling.
Devoicing of voiced stops in German A trivial (if all-pervasive) example of conditioned merger is the devoicing of voiced stops in German when in word-final position or immediately before a compound boundary (see: Help:IPA/Standard German):
*hand "hand" > (cf. plural /ˈhɛndə/) "wrist" *bund "league, association" > (cf. plural /ˈbʏndə/) *gold "gold" > (cf. "golden" ) *halb "half" > // (cf. "to halve" ) halbamtlich "semi-official" *berg "mountain" (cf. plural ) *klug "clever, wise" > (cf. fem. )
There were, of course, also many cases of original voiceless stops in final position: "bed", "colorful", "(walking) stick, cane". To sum up: there are the same number of structure points as before, , but there are more cases of than before and fewer of , and there is a gap in the distribution of (they are never found in word-final position or before a compound boundary).
Note 1: this split is easily recoverable by internal reconstruction because it results in alternations whose conditions are transparent. Thus "bunch" (as of keys) has a plural in contrast to "colorful" with in all environments (feminine /, neuter and so on). In a neutralizing environment, such as a voiceless stop in word-final position, one cannot tell which of two possibilities was the original sound. The choice is resolved if the corresponding segment can be found in a non-neutralizing position, as when a suffix follows. Accordingly, a non-inflected form like "and" is historically opaque (though as the spelling hints, the was originally */d/).
Note 2: unlike most phonological changes, this one became a "surface" rule in German, so loan-words whose source had a voiced stop in the devoicing environment are taken into German with a voiceless one instead: "club" (association) from English club. The same goes for truncated forms: (for formal "boy") is . Note 2a: the surface alternation is what allows modern German orthography to write stops morphophonemically, thus "loaf", "hand", "way", all with voiceless final stops in the simplex form and in compounds, but in inflected forms. In Old High and Middle High German, all voiceless stops were written as pronounced: hleip, hant, uuec and so on.
Note 3: the same distribution holds for vs. , but it arose by a completely different process, the voicing of original */s/ between vowels: *mūs "mouse" > , *mūsīz "mice" (for earlier *mūsiz) > . Original long (now short) ss does not voice medially, as in "to kiss" , nor does /s/ from Proto-West-Germanic *t, as in "water" , "kegs" plural of (= English vat), "idle" . German , as in "fish", reflects original *sk (in native words) and does not become voiced in any environment: "fisherman" . (German has only in loanwords: "genius", "salary".)
Rhotacism in Latin More typical of the aftermath of a conditioned merger is the famous case of rhotacism in Latin (also seen in some Sabellian language spoken in the same area): Proto-Italic *s > Latin between vowels: *gesō "I do, act" > Lat. (but perfect < *ges-s- and participle < *ges-to-, etc., with unchanged *s in all other environments, even in the same paradigm).
This sound law is quite complete and regular, and in its immediate wake there were no examples of /s/ between vowels except for a few words with a special condition ( "wretched", "bushy hair", diser(c)tus "eloquent": that is, rhotacism did not take place when an /r/ followed the *s). However, a new crop of /s/ between vowels soon arose from three sources. (1) a shortening of /ss/ after a diphthong or long vowel: "lawsuit" < *kawssā, "house' < *kāssā, "poured, melted" < *χewssos. (2) univerbation: (nisī) "unless" < the phrase *ne sei, (quasī) "as if" < the phrase *kʷam sei. (3) borrowings, such as "rose" /rosa/, from a Sabellian source (the word is clearly somehow from Proto-Italic *ruθ- "red" but equally clearly not native Latin), and many words taken from or through Greek (, etc.).
Nasal assimilation and "gn" in Latin
A particular example of a conditioned merger in Latin is the rule whereby syllable-final stops, when followed by a nasal consonant, assimilated with it in nasality, while preserving their original point of articulation:
*supimos > *supmos > summus "highest" *sabnyom > Samnium "Samnium" (a region in the southern Apennines) *swepnos > somnus "sleep" *atnos > annus "year"
In some cases, the underlying (pre-assimilation) root can be retrieved from related lexical items in the language: e.g. superior "higher"; Sabīni "Samnites"; sopor "(deep) sleep". For some words, only comparative evidence can help retrieve the original consonant: for example, the etymology of "year" (as *atnos) is revealed by comparison with Gothic aþna "year".
According to this rule of nasal assimilation, the sequences *-g-n and *-k-n would become , with a velar nasal : *dek-no- > dignus [diŋnus] "worthy" *leg-no- (*leǵ- "gather") > lignum [liŋnum] "firewood" *teg-no- (*(s)teg- "build") > tignum [tiŋnum] "timber" *agʷnos > *ag-nosThe same PIE root *H₂egʷnós yielded Greek ἀμνός "lamb". In Latin, PIE labiovelars were regularly delabialized before another consonant: "left behind" < *likʷ-to- (cf. "leave behind", Greek ). > agnus [aŋnus] "lamb"
The sound was not a phoneme of Latin, but an allophone of before .