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In historical linguistics, phonological change is any sound change which alters the number or distribution of phonemes in a language. In a typological scheme first systematized by Henry M. Hoenigswald, 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== Purely phonetic change involves no reshuffling of the contrasts of a phonological system. All phonological systems are complex affairs with many small adjustments in phonetics depending on phonetic environment, position in the word, and so on. For the most part, phonetic changes are examples of allophonic differentiation or assimilation, that is, sounds in specific environments acquire new phonetic features or perhaps lose phonetic features they originally had. For example, the devoicing of the vowels and in certain environments in Japanese, the nasalization of vowels before nasals (commonplace, though not universal), changes in point of articulation of stops and nasals under the influence of adjacent vowels. "Phonetic" means 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 would not qualify as phonological change as long as all of these phones remained in complementary distribution. Many phonetic changes provide the raw ingredients for later phonemic innovations. In Proto-Italic, for example, intervocalic */s/ became *(). This was a phonetic change, a mild and superficial complication in the phonological system only, but when this *() merged with */r/, the effect on the phonological system was greater. (This 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 only occurred in this 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. That is, the difference became phonemic. (This "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 do not as a rule 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 whatever on preceding velar stops. A potential incipient example of allophones producing phonological change can be seen in child acquisition of English. In American and some varieties of British English, the phoneme has a distinctly ''rounded'' pronunciation at the onset of a stressed syllable, particularly at the beginning of a word, regardless of the following vowel. (Some rounding would be expected before a round vowel.) That is, the words ''round, rich, reason, rat'' all begin with a labialized ar .〔Indeed, in a dialect heard around New York City, is pronounced , that is, the labialization has become the primary articulation, a voiced labiodental fricative but with coarticulated tongue-bunching such that ''real'' and ''veal'' remain distinct, though outsiders might well take them for homophones.〕 In many English dialects this rounding is salient enough that many small children, and even some adult native speakers, have only a vestigial bunching of the tongue body in such words, or none at all, so that the rounding is all that remains. The effect is that for such speakers ''rich'' and ''witch'' are very similar or even identical in pronunciation. This is the "Elmer Fudd" effect: ''I'll get that wascally wabbit,'' and so on. This rounding feature is the product of the merger of two earlier phonemes, a rounded ''r'' and a plain ''r'' , dating from Old English. This contrast was only found in word-initial position, and survived late enough in Middle English to become enshrined in our standard spelling, as ''wretch'' vs ''retch,'' ''wring'' vs ''ring,'' and so on. In the mid-15th century we start finding spelling confusions indicating that the contrast between and had been lost, as initial acquired rounding. That is, what were originally two different phonemes found themselves in complementary (mutually exclusive) distribution, a single phoneme pronounced in initial and stressed positions and in other positions. Thus the features of English ''r''-phonetics are in part due to phonemic merger, not mere change in pronunciation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Phonological change」の詳細全文を読む スポンサード リンク
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