The following is from the tone sandhi section of a writeup on Wu I've been working on for Phonemica. It's a draft of a single section. The full version will appear on Phonemica in the near future. I've decided to post it here in its current form in case it proves useful to have a clearer explanation than some of the other sources on the topic.
Wu dialects typically have 7 or 8 tones which follow the traditional system of four tones (ping, shang, qu, ru) with two registers (yin and yang). Tone sandhi — the way in which tones interact with eachother — is remarkable in a number of dialects, most notably that spoken in urban Shanghai.
In Mandarin, tone sandhi is limited to a few specific combinations, such as when two dipping tones becoming a rising followed by a dipping tones, e.g. 老虎 lǎohǔ becomes láohǔ. However in dialects of Wu, specifically in the northern Taihu dialects which we’ll look at here, the tones follow a set pitch contour that runs throughout a whole multi-syllabic word or phrase. This contour can be determined in one of two ways.
First, for multisyllabic words, the contour is determined by the first syllable and follows a pattern based on the number of syllables in the word. The following is an example from the Changzhou Taihu dialect. Two four-syllable words are given below, the second having different syllable-level tones than the first. The numbers correspond to the tones of the characters in isolation, 1 being low and 5 being high, thus 24 indicates a rising tone while 55 is a high level tone.
大清老早 → 大24 清55 老45 早45
動手動腳 → 動24 手45 動24 腳55
Since it is the first or left-most syllable that determines the pattern, we say that word-based sandhi is left-prominent. In these cases, That is, the tones of the other syllables in the word are ignored in favour of those assigned by the phrase contour called upon by the first. Since both of these examples begin with a syllable having a mid-rising (24) tone contour, and since both are 4 syllables in length, the resulting contour for both phrases should be the same after sandhi changes, which are as follows:
大24 清55 老45 早45 → 大21 清21 老44 早21
動24 手45 動24 腳55 → 動21 手21 動44 腳21
Despite these two examples having different underlying tones, the left-prominent sandhi system assigns both words the same surface contours since they share a tone on the first syllable. In the dialect of Changzhou, a four-syllable word beginning in a yang-qu tone (the above 24 tone) will always result in a overall contour like that above, with the stress falling on the third syllable. For this reason, it is often said that Northern Wu isn’t a tonal language in the typical sense, but rather should be considered a pitch accent system like some dialects of Japanese and Korean. Of course, different Wu dialects have different ways of handling the tones. In most Northern Wu dialects, however, we should expect a system like that outlined above.
As mentioned above, for multi-syllabic words, the sandhi system is referred to as left-prominent. That is, only the left-most syllable matters for the overall contour. However for bi-syllabic phrases which themselves do not make up single words, the sandhi rules are different. In these multi-word phrases, the system is right-prominent. That is, the right syllable retains its original tone, while the left syllable is neutralised within its register (yin or yang, as mentioned above). Looking at and example from urban Shanghainese, we have the phrase 讀書 /dɤ sɿ/. These two characters have two different readings: to read a book and to study. Since to read a book is a phrase, it would have a different tone contour than the same syllables meaning to study, the latter being a single word in Shanghainese. The phrase would have application tone sandhi as follows based on word-based left-prominent sandhi and phrase-based right-prominent sandhi:
to read a book (right-prominent phrase)
讀12書53 → 讀22書53 / 12 53 → 22 53
to study (left-prominent word)
讀12書53 → 讀11書23 / 12 53 → 11 23
In the first example, to read a book, The tone on 讀 is 24 in isolation, however it is an entering tone and so it gets neutralised to 22. 書 retains its original tone of 53 because it’s the prominent word in the phrase. In the second example, to study functions as a single word, so that the tonal curve of the whole word is determined by 讀. Like the four-syllable example above, two-syllable words also have set contours, and the contour for such sentences beginning with an entering-tone syllable is 11.23. Thus, in the example of to study, the tone on both syllables is modified from the isolated tone, however it’s happening in a pattern determined by the first syllable.
In addition to the set word-level contours, there are set values for tone neutralisation in phrase-level sandhi. Specifically, yin tones neutralise to 44 while yang tones neutralise to 33. The exception is for the ru class of tones, in which case the tone is neutralised to 22 regardless of register..
This again is common in Northern Wu dialects, though each dialect will follow a set of sandhi rules unique to that dialect. For that reason we won’t go into more detail here.
- 朱曉農 Zhu Xiaonong，A Grammar of Shanghai Wu，Lincom Europa，München，2006