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|Sound change and alternation|
Sandhi (Sanskrit: संधि saṃdhí "joining") is a cover term for a wide variety of phonological processes that occur at morpheme or word boundaries (thus belonging to what is called morphophonology). Examples include the fusion of sounds across word boundaries and the alteration of sounds due to neighboring sounds or due to the grammatical function of adjacent words. Sandhi occurs particularly prominently in the phonology of Indian languages (especially Telugu, Tamil, Kannada, Malayalam language, Marathi, Bengali and most importantly Sanskrit, which have complex sandhi rules), hence its name, but many other languages have it.
- Internal sandhi features the alteration of sounds within words at morpheme boundaries, as in sympathy (syn- + pathy).
- External sandhi refers to changes found at word boundaries, such as in the pronunciation tem books for ten books in some dialects of English. The linking r of some dialects of English is a kind of external sandhi, as is the process called liaison in the French language and raddoppiamento fonosintattico in Italian.
While it may be extremely common in speech, sandhi (especially for the external) is typically ignored in spelling, as is the case in English, with the exception of the distinction between "a" and "an" (sandhi is, however, reflected in the writing system of both Sanskrit and many other Indian languages, as also in Italian in the case of compound words with lexicalized raddoppiamento fonosintattico).
In Japanese phonology, sandhi is primarily exhibited in rendaku (consonant mutation from voiced to unvoiced 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, 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 /n/ on one morpheme results in an /n/ (or /m/) being added to the start of the next morpheme, as in 「天皇」 てん ＋ おう → てんのう (ten + ō = tennō); this is also shown in the spelling (as done here – the kanji do not change, but the kana, which specify pronunciation, do change). See 連声 for further examples.
Most tonal languages have tone sandhi, in which the tones of words alter according to pre-determined rules. An example is the behavior of tone 3 in Mandarin Chinese. Mandarin has four tones, and 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 occurring before any of the other tones, it is pronounced as a low falling tone, with no rise at the end. A simple example of this occurs in the common greeting nǐ hǎo (with two words containing underlying tone 3), which is normally pronounced as if written ní hǎo.
See also 
- Alternation (linguistics)
- Liaison (French)
- Linking and intrusive R
- Movable nu
- the pronunciation of the word "sandhi" is rather diverse among English speakers. In Sanskrit it is pronounced [sən̪d̪ʱi]. English pronunciations include // (identical with "Sunday" for some British English speakers), // (like the first name "Sandy"), and //.
- Harold F. Schiffman, A Reference Grammar of Spoken Tamil, Cambridge University Press, 1999, p. 20.