I noticed that sometimes certain finals in Chinese sound differently when combined with different initials. For e.g., what is spelled "u" sometimes is pronounced "ü". Other times, I think the final "i" sounds differently when combined with different initials. Is there a list of rules explaining all of these differences within standard Mandarin?
The pronunciations of finals do not change when used after different finals, with perhaps only one exception: 'i'. It has three variations: 'zi ci si', 'zhi chi shi ri', and all others.
NOTE: Not many Chinese know the differences, but you can compare:
English pinyin Lee li she shi (the two consonants are also different) see si
The three english /ee/ in the above word are the same, but the three Chinese i are all different.
However, the spellings of the finals do change when used after different initials. The details can be found in 汉语拼音方案 (the Scheme for the Chinese Phonetic Alphabet), which is the official standard for Chinese pinyin.
For the example mentioned by the OP, 'ü' will be written as 'u' after 'j' 'q' and 'x'. ('u' will never be used after 'j' 'q' or 'x')
I think one of the reasons is the loss of tone and/or stress in the syllable. But see this table, "Chinese (Mandarin)/Pronunciation of Finals", it provides a good summary of the changes.
One of the easiest ways to hear the different pinyin sounds is to look on YouTube. The trickiest ones for me to learn were the different pronunciations of "i". Here are some videos that explain the differences:
- zhi, chi, shi, r sound a bit like English "sure".
- ji, qi, xi sound a bit like English "she".
- zi, ci, si sound a bit like the vowel at the end of "visa".
There are lots more YouTube videos about pinyin sounds.
'U' is pronounced 'Ü' with the initials J, Q, X and the pseudo-initial 'Y'. Otherwise it is always pronounced 'U'.
Something that might help one remember it, is that J, Q and X are also pronounced with the same tongue-position but with slightly varying flow of air. So J, Q and X are basically one pronunciation.
I like to think that the inventors of pinyin wanted to save some trouble, and decided to spare the writers of pinyin the hassle (and ink) of writing the umlaut above the 'U', when it is not absolutely necessary. (It does pose a challenge for learners though).
Some pinyin charts can help you remember it by visualization. On the chart below you'll see the 'Ü' pronunciation is grouped regardless of how it is written ('Ü' or not)
My mothertongue teacher suggested the following "Pinyin false friends list". She spoke about the "7+3+5" false friends:
- The 7 are
z c s zh ch sh r, after which
iis pronounced, she said, as "silence"; this, as I said in a comment, equates to either always /ɨ/ or, more accurately, a trailing syllabic voiced fricative, i.e.
zi ci si zhi chi shi ri=
/tsz̩ tsʰz̩ sz̩ tʂʐ̩ tʂʰʐ̩ ʂʐ̩ ɻʐ̩/, or one may say
/ʐʐ̩/, that varies from speaker to speaker;
- The 3 are
j q x, after which
uis pronounced like
üin any case; that is because
j q xare alveolo-palatal, and are thus never used before non-palatal sounds like u; that also explains why
z c s zh ch sh rhave the above sounds with
-i: i is palatal, they are not; in fact, what used to be
*/tsi/etc. "collapsed" into modern
jietc., and so did
*gietc, according to Wikipedia; this is why
Beijing: it used to be
*Beigingand got Wade-Giles
Pei-king, and lost the
ifor "English phonetic representation";
- The 5 are
ui iu ian üan o, which are pronounced as
uei iou ien üen werespectively.
Now I do not agree to the
o. Or rather, it needs specifications.
o by itself is, AFAIK, only present in the 4 characters
哦喔噢嚄, which are interjections and exclamative particles, and which I would pronounce
/o/ – I'm not a native though, so this must be taken cum grano salis, and they are sometimes rendered as
o is a syllable final (e.g.
bo po mo fo, actually those are the only examples, as elsewhere you find
uo) it is usually pronounced
/wo/. Wikipedia has this table and note three in this one agreeing with this view. Also, this Wiktionary entry, for example, translates
/-u̯o/, which is essentially
/-wo/. With this, I think the 7+3+5 rule is a good mnemonic for these spelling-sound discrepancies.
See also here for further reading and comparisons with other Romanizations such as Wade-Giles.
There is also another thing: tone sandhi (Chinese
连续变调). Basically, third tones often change. Base rule: 3+3 -> 2+3, i.e. nǐhǎo is pronounced níhǎo. For sequences, see here and linked questions. There are also tone variations of
不, which are sometimes marked, but often not marked. For those, if you are not satisfied with this, I suggest you ask another question.