សូរ (​ភាសាសាស្ត្រ​): Origin {{anchor|Origin}}

Origin 

André-Georges Haudricourt established that Vietnamese tone originated in earlier consonantal contrasts, and suggested similar mechanisms for Chinese.The seminal references are two Haudricourt articles published in 1954 and 1961 It is now widely held that Old Chinese did not have phonemically contrastive tone. The historical origin of tone is called tonogenesis, a term coined by James Matisoff. Tone is frequently an areal rather than a genealogical feature. That is, a language may acquire tones through bilingualism if influential neighboring languages are tonal, or if speakers of a tonal language shift to the language in question, and bring their tones with them. In other cases, tone may arise spontaneously, and surprisingly quickly: the dialect of Cherokee in Oklahoma has tone, but the dialect in North Carolina does not, although they were only separated in 1838.

Very often, tone arises as an effect of the loss or merger of consonants. (Such trace effects of disappeared tones or other sounds have been nicknamed Cheshirisation, after the lingering smile of the disappearing Cheshire Cat in Alice in Wonderland.) In a non-tonal language, voiced consonants commonly cause following vowels to be pronounced at a lower pitch than other consonants do. This is usually a minor phonetic detail of voicing. However, if consonant voicing is subsequently lost, that incidental pitch difference may be left over to carry the distinction that the voicing had carried, and thus becomes meaningful (phonemic). This is seen historically in Panjabi: the Panjabi murmured (voiced aspirate) consonants have disappeared, and left tone in their wake. If the murmured consonant was at the beginning of a word, it left behind a low tone; if at the end, a high tone. If there was no such consonant, the pitch was unaffected; however, the unaffected words are limited in pitch so as not to interfere with the low and high tones, and so has become a tone of its own: mid tone. The historical connection is so regular that Panjabi is still written as if it had murmured consonants, and tone is not marked: the written consonants tell the reader which tone to use.

Similarly, final fricatives or other consonants may phonetically affect the pitch of preceding vowels, and if they then weaken to /h/ and finally disappear completely, the difference in pitch, now a true difference in tone, carries on in their stead. This was the case with the Chinese languages: Two of the three tones of Middle Chinese, the "rising" and "departing" tones, arose as the Old Chinese final consonants  and  disappeared, while syllables that ended with neither of these consonants were interpreted as carrying the third tone, "even". Most dialects descending from Middle Chinese were further affected by a tone split, where each tone divided in two depending on whether the initial consonant was voiced: Vowels following a voiced consonant (depressor consonant) acquired a lower tone as the voicing lost its distinctiveness.

The same changes affected many other languages in the same area, and at around the same time (AD 1000–1500). The tone split, for example, also occurred in Thai, Vietnamese, and the Lhasa dialect of Tibetan.

In general, voiced initial consonants lead to low tones, while vowels after aspirated consonants acquire a high tone. When final consonants are lost, a glottal stop tends to leave a preceding vowel with a high or rising tone (although glottalized vowels tend to be low tone, so if the glottal stop causes vowel glottalization, that will tend to leave behind a low vowel), whereas a final fricative tends to leave a preceding vowel with a low or falling tone. Vowel phonation also frequently develops into tone, as can be seen in the case of Burmese.

Tone arose in the Athabascan languages at least twice, in a patchwork of two systems. In some languages, such as Navajo, syllables with glottalized consonants (including glottal stops) in the syllable coda developed low tones, whereas in others, such as Slavey, they developed high tones, so that the two tonal systems are almost mirror images of each other. Syllables without glottalized codas developed the opposite tone—for example, high tone in Navajo and low tone in Slavey, due to contrast with the tone triggered by the glottalization. Other Athabascan languages, namely those in western Alaska (such as Koyukon) and the Pacific coast (such as Hupa), did not develop tone. Thus, the Proto-Athabascan word for "water"  is toneless  in Hupa, high-tone  in Navajo, and low-tone tù in Slavey; while Proto-Athabascan  "knee" is toneless  in Hupa, low-tone  in Navajo, and high-tone  in Slavey. Kingston (2005) provides a phonetic explanation for the opposite development of tone based on the two different ways of producing glottalized consonants with either (a) tense voice on the preceding vowel, which tends to produce a high F0, or (b) creaky voice, which tends to produce a low F0. Languages with "stiff" glottalized consonants and tense voice developed high tone on the preceding vowel and those with "slack" glottalized consonants with creaky voice developed low tone.

The Bantu languages also have "mirror" tone systems, where the languages in the northwest corner of the Bantu area have the opposite tones of other Bantu languages.

Three Algonquian languages developed tone independently of each other and of neighboring languages: Cheyenne, Arapaho, and Kickapoo. In Cheyenne, tone arose via vowel contraction; the long vowels of Proto-Algonquian contracted into high-pitched vowels in Cheyenne, while the short vowels became low-pitched. In Kickapoo, a vowel with a following [h] acquired a low tone, and this tone later extended to all vowels followed by a fricative.

In Mohawk, a glottal stop can disappear in a combination of morphemes, leaving behind a long falling tone. Note that this has the reverse effect of the postulated rising tone in Mandarin derived from a lost final glottal stop.