Tone letter

Tone letters are letters that represent the tones of a language, most commonly in languages with contour tones.

A series of iconic tone letters based on a musical staff was devised by Yuen Ren Chao in the 1920s by adding a reference stave to the existing convention of the International Phonetic Alphabet. The stave was adopted by the IPA as an option in 1989 and is now nearly universal. When the contours had been drawn without a staff, it was difficult to discern subtle distinction in pitch. Only nine or so of the possible tones were commonly distinguished: high, medium and low level, [ˉa ˗a ˍa] (or as dots rather than macrons for 'unaccented' tones); high rising and falling, [ˊa ˋa]; low rising and falling, [ˏa ˎa]; and peaking and dipping, [ˆa ˇa], though more precise notation was found and the IPA specifically provided for mid rising and falling tones if needed. The Chao tone letters were originally x-height, but are now taller to make distinctions in pitch more visible.

Combinations of the Chao tone letters form schematics of the pitch contour of a tone, mapping the pitch in the letter space and ending in a vertical bar. For example, [ma˨˩˦] represents the mid-dipping pitch contour of the Chinese word for horse, 馬／马 mǎ. Single tone letters differentiate up to five pitch levels: ˥ 'extra high' or 'top', ˦ 'high', ˧ 'mid', ˨ 'low', and ˩ 'extra low' or 'bottom'. No language is known to depend on more than five levels of pitch.

These letters are most commonly written at the end of a syllable. For example, Standard Mandarin has the following four tones in syllables spoken in isolation:

For languages that have simple register tones in basic morphemes, or on short vowels, single tone letters are used for these, and the tone letters combine as the tones themselves do to form contours. For example, Yoruba has the three basic tones [˥ ˧ ˩] on short vowels and the six derived contour tones [˥˧ ˥˩ ˧˥ ˧˩ ˩˧ ˩˥] on long vowels, diphthongs and contractions. On the other hand, for languages that have basic contour tones, and among these are level tones, it's a common convention to use double tone letters for those level tones, and single tone letters for short checked tones, as in Taiwanese Hokkien [sã˥˥] vs [tit˥]. The tones [˥˥] and [˥] are generally analyzed as being the same phoneme, and the distinction reflects traditional Chinese classification; it also derives from the convention of numerically writing ⟨sã55⟩ for high level pitch vs ⟨sã5⟩ for tone #5. Regardless, this is not an IPA convention.

Chao tone letters are sometimes written before the syllable, in accordance with writing stress and downstep before the syllable, and as had been done with the unstaffed letters in the IPA before 1989. For example, the following passage transcribes the prosody of European Portuguese using tone letters alongside stress, upstep, and downstep in the same position before the syllable:

The two systems may be combined, with prosodic pitch written before a word or syllable and lexical tone after a word or syllable, since in the Sinological tradition the tone letters following a syllable are always purely lexical and disregard prosody.

Diacritics may also be used to transcribe tone in the IPA. For example, tone 3 in Mandarin is a low tone between other syllables, and can be represented as such phonemically. The four Mandarin tones can therefore be transcribed /má, mǎ, mà, mâ/. (These diacritics conflict with the conventions of Pinyin, which uses the pre-Kiel IPA diacritic conventions: ⟨mā, má, mǎ, mà⟩, respectively)