Tone sandhi

Tone sandhi (Sandhi is from Sanskrit meaning, "putting together") refers to the pitch change in tones when different tones come together. For example, in Mandarin Chinese the most common tone sandhi rule is that a low-tone syllable (third tone) is changed to a rising tone (second tone) when it is followed by another low tone. This is demonstrated in the phrase nǐhǎo (pinyin, Chinese characters 你好), the most common Mandarin greeting, which is actually pronounced níhǎo. These tone-changing processes are active in all tonal languages, but they seem to be more common in some than in others.

While certain languages (such as Mandarin in the above example) exhibit a fairly constant set of rules for Tone Sandhi, other forms, such as Hakka, are more complex. Southern Min is still more complex, with the most complex systems found in Wu and Jin.

"Tone sandhi", which is compulsory as long as the environmental conditions are met, is not to be confused with tone changes that reflect derivational or inflectional morphology. For example, in Cantonese when 糖 is pronounced "tong4", it means 'sugar', whereas when it is pronounced "tong2", it means "candy". In Taiwanese (Min Nan) morphemes, kiaⁿ (afraid) and lâng (person) may combine to form the word kiaⁿ-lâng, whose meaning varies according to the tone change. When pronounced "kiaⁿ7-lâng", it means "to be afraid of people". When pronounced "kiaⁿ1-lâng", it means "frightful".

Cherokee has a robust tonal system in which tones may be combined in various ways, following subtle and complex tonal rules that vary from community to community.

Sandhi rules are also found in many of the Oto-Manguean languages of Mexico.