Sandhi

Sandhi (सन्धि, ) is any of a wide variety of sound changes that occur at morpheme or word boundaries. Examples include fusion of sounds across word boundaries and the alteration of one sound depending on nearby sounds or the grammatical function of the adjacent words. Sandhi belongs to morphophonology.

Sandhi occurs in many languages, e.g. in the phonology of South Asian languages (especially Sanskrit, Tamil, Sinhala, Telugu, Marathi, Hindi, Pali, Kannada, Bengali, Assamese, Malayalam). Many dialects of British English show linking and intrusive R.

A subset of sandhi called tone sandhi more specifically refers to tone changes between words and syllables. This is a common feature of many tonal languages such as Mandarin Chinese.

Internal and external sandhi
Sandhi can be either
 * internal, at morpheme boundaries within words, such as syn- + pathy: sympathy, or
 * external, at word boundaries, such as the pronunciation "tem books" for ten books in some dialects of English. The linking process of some dialects of English ("I saw-r-a film" in British English) is a kind of external sandhi, as are French liaison (pronunciation of usually silent final consonants of words before words beginning with vowels) and Italian raddoppiamento fonosintattico (lengthening of initial consonants of words after certain words ending in vowels).

It may be extremely common in speech, but sandhi (especially external) is typically ignored in spelling, as is the case in English (exceptions: the distinction between a and an; the prefixes con-, en-, in- and syn-, whose n assimilates to m before p, m or b). Sandhi is, however, reflected in the orthography of Sanskrit, Sinhala, Telugu, Marathi, Pali and some other Indian languages, as with Italian in the case of compound words with lexicalised syntactic gemination.

External sandhi effects can sometimes become morphologised (apply only in certain morphological and syntactic environments) as in Tamil and, over time, turn into consonant mutations.

Tone sandhi
Most tonal languages have tone sandhi in which the tones of words alter according to certain rules. An example is the behavior of Mandarin Chinese; in isolation, tone 3 is often pronounced as a falling-rising tone. When a tone 3 occurs before another tone 3, however, it changes into tone 2 (a rising tone), and when it occurs before any of the other tones, it is pronounced as a low falling tone with no rise at the end.

An example occurs in the common greeting 你好 nǐ hǎo (with two words containing underlying tone 3), which is in practice pronounced ní hǎo. The first word is pronounced with tone 2, but the second is unaffected.

Celtic languages
In Celtic languages, the consonant mutation sees the initial consonant of a word to change according to its morphological or syntactic environment. Following are some examples from Breton, Irish, Scottish Gaelic, and Welsh:

English
In English phonology, sandhi can be seen when one word ends with a vowel, and the next begins with a vowel. An approximant is inserted between them based on the vowel ending the first word: if it is rounded, e.g. [ʊ], a [w] (voiced labial-velar approximant) is inserted. The vowels [iː], [ɪ], and [ɪː] (including [ɛɪ], [ɑɪ], and [ɔɪ]) take a sandhi of [j] (voiced palatal approximant). All other vowels take [ɹ] (voiced alveolar approximant) (see linking and intrusive R). For example, "two eggs" is pronounced [tuːw.ɛɡz], "three eggs" is [θɹiːj.ɛɡz], and "four eggs" is [fɔːɹ.ɛɡz].

In some situations, especially when a vowel is reduced to a schwa, certain dialects may instead use a glottal stop [ʔ]. For example, "gonna eat" may be pronounced as [ɡʌn.əw.iːt], reflecting the [uː] sound that has been reduced, or as [ɡʌn.əɹ.iːt], reflecting the schwa sound, which takes a sandhi of [ɹ], or as [ɡʌn.ə.ʔiːt], using a glottal stop to separate the words. Note that in this case the glottal stop occurs at the start of "eat" rather than at the end of "gonna". A glottal stop sandhi is especially done when wishing to avoid other, more noticeable, sandhi due to stress; if, in the above example, either the last syllable of "gonna" was stressed, or there was particular stress on the word "eat", a glottal stop would generally be the preferred sandhi.

French
French liaison and enchaînement can be considered forms of external sandhi. In enchaînement, a word-final consonant, when followed by a word commencing with a vowel, is articulated as though it is part of the following word. For example, sens (sense) is pronounced and unique (unique) is pronounced ; sens unique (one-way, as a street) is pronounced.

Liaison is a similar phenomenon, applicable to words ending in a consonant that was historically pronounced but that, in Modern French, is normally silent when occurring at the end of a phrase or before another consonant. In some circumstances, when the following word commences with a vowel, the consonant may be pronounced, and in that case is articulated as if part of the next word. For example, deux frères (two brothers) is pronounced with a silent, and quatre hommes (four men) is pronounced , but deux hommes (two men) is pronounced.

Japanese
In Japanese phonology, sandhi is primarily exhibited in rendaku (consonant mutation from unvoiced to voiced when not word-initial, in some contexts) and conversion of つ or く (tsu, ku) to a geminate consonant (orthographically, the sokuon っ), both of which are reflected in spelling – indeed, the っ symbol for gemination is morphosyntactically derived from つ, and voicing is indicated by adding two dots as in か／が ka, ga, making the relation clear. It also occurs much less often in renjō (連声), where, most commonly, a terminal on one morpheme results in an  (or ) being added to the start of the next morpheme, as in 天皇: てん ＋ おう → てんのう (ten + ō = tennō), meaning "emperor"; that is also shown in the spelling (the kanji do not change, but the kana, which specify pronunciation, change).

Korean
Korean has sandhi which occurs in the final consonant or consonant cluster, such that a morpheme can have two pronunciations depending on whether or not it is followed by a vowel. For example, the root 읽, meaning ‘read’, is pronounced before a consonant, as in 읽다 , but is pronounced like  before vowels, as in 읽으세요 , meaning ‘please read’. Some roots can also aspirate following consonants, denoted by the letter ㅎ (hieut) in the final consonant. This causes 다  to become  in 않다, ‘to not be’.

Tamil
As Tamil is strongly characterised by diglossia : there are two separate registers varying by socioeconomic status, a high register and a low one. This in turn adds an extra layer of complexity forming Sandhi. Tamil employs Sandhi for certain morphological and syntactic structures.

Vowel position
The vowel sandhi occurs when words or morphemes ending in certain vowels are followed by morphemes beginning with certain vowels. Consonant glides (ய் and வ்) are then inserted between the vowels in order to 'smooth the transition' from one vowel to another.

"The choice of whether the glide inserted will be (ய் and வ்) in Tamil is determined by whether the vowel preceding the glide is a front vowel such as இ, ஈ, எ, ஏ or ஐ or a back vowel, such as உ, ஊ, ஒ, ஓ, அ or ஆ."

Sandhi following back vowels
In rapid speech, especially in polysyllabic words: இந்த்யாவுலேருந்து may become — இந்த்யாலெருந்து, which may then be further simplified to இந்த்யாலெந்து.

Elision
In Spoken Tamil the final laterals, nasals or other sonorants may lose the final position. The final retroflex laterals for pronouns and their PNG markers for example ள் of (female gender marker) are deleted: (To indicate the omitted stop-consonant is covered in parantheses): அவ(ள்) போறா(ள்).

Noun cases
In some nouns, sandhi is triggered by the addition of a case ending to the stem.