Hanyu Pinyin is not an orthography where there is a one-to-one mapping of letters (graphemes) to sounds (phonemes). This is because of the several abbreviations that are made. These abbreviations make pinyin easier to use for those familiar with the system, but unintuitive for those who are new to it. A spelling in hanyu pinyin may mislead learners, and it's important to keep in mind when something is not pronounced as it's spelled.
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In three cases, an abbreviation is made by removing a letter:
- -iou = -iu
- -uei = -ui
- -uen = -un
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Where no ambiguity would arise, vowels with diacritics are written without a diacritic
for convenience. The sound [ɛ] (like English red) was originally represented by
ê, but everywhere that it occurs, it is replaced.
- -iê = -ie
- -iên = -ian
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If the initial is j, q, or x, replace ü with u.
- (jqx)-ü = -u
- (jqx)-üê = -ue
- (jqx)-üên = -uan
- (jqx)-ün = -un
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In most cases, if there is no initial, the spelling is altered to make syllable
boundaries unambiguous when syllables are written together. In the case when there's
no initial and there is an ü, replace ü with yu.
- ü = yu
- üê = yue
- üên = yuan
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If there's no initial and the vowel is i (with no diphthong), add a y:
- i = yi
- in = yin
- ing = ying
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If there's no initial and there is a diphthong beginning with i, replace i with y.
- iê = ye
- iên = yan
- iou = you
- ia = ya
- iao = yao
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If there's no initial and the final is just u, add a w:
- u = wu
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If there's no initial and there is a diphthong beginning with u, replace u with w.
- ua = wa
- uai = wai
- uei = wei
- uan = wan
- uen = wen
It's also important to remember that -i represents a different sound depending on whether the initial is one of {sh, ch, zh, r}, {z, c, s}, or {b, p, m, d, t, n, l, j, q, x}. There are other differences in the sound that one letter represents between different finals, but these are less misleading.