語音降階
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Revision as of 20:25, 25 March 2006
在語音學上，語音降階(downstep) is a phonemic or phonetic downward shift of tone between the syllables or words of a tonal language. It is best known in the languages of West Africa, but the pitch accent of Japanese (a non-tonal language) is quite similar to downstep in Africa. Downstep contrasts with the much rarer upstep. The symbol for downstep in the 國際音標 is a superscript down arrow, ↓, which is not yet supported by Unicode. It is common to see a superscript exclamation mark, !, used instead.
Phonetic downstep may occur between sequences of the same phonemic tone. For example, when two mid tones occur together in Twi, the second is at a lower pitch than the first. Thus downshift plays a vital role in downdrift and tone terracing.
Phonemic downstep may occur when a low tone is elided, or occurs as a floating tone, and leaves a following tone at a lower level than it would otherwise be. An example occurs in 班巴拉語. In this language, the 定冠詞 is a floating low tone. With a noun in isolation, it docks to the preceding vowel, turning a high tone into a falling tone: [bá] river; [bâ] the river. However, when it occurs between two high tones, it downsteps the following tone: [bá tɛ́] it's not a river; [bá ↓ tɛ́] it's not the river.
Japanese pitch accent is similar. About 80% of Japanese words have an evenly rising pitch, something like French, which carries over onto following unstressed grammatical particles. However, a word may have a drop in pitch between moras, or before the grammatical particle. An example is
| /ka↓ki/ | /kaki↓/ | /kaki/ |
| [kákì] | [kàkí] | [kàkí] |
| oyster | fence | persimmon |
In isolation like this, the first word has a high-low pitch, whereas the second and third are homonyms with a low-high pitch. However, all three are distinct when followed by the so-called "subject" particle ga:
| /ka↓kiga/ | /kaki↓ga/ | /kakiga/ |
| [kákìgà] | [kàkígà] | [kàkīgá] |
| oyster | fence | persimmon |
