I had been interested in the idea that tone contours are due to practical limitations in following an underlying target path that is always a straight line, as proposed by Xu. However, this theory seems to me to imply that the citation forms will be the same or nearly the same as the underlying targets, which is demonstrably not the case. I posted about that here but didn’t get any response, so have put Xu's approach on one side for now.
As I understand autosegmental theories, each segment of the rime is supposed to carry a unitary instruction or gesture like ‘up’ or ‘down’.
I know that in Thai, there are some words whose rimes consist of a short vowel but which nevertheless have a falling tone. Examples would be ก็ or ค่ะ. This as I understand it requires two instructions (up then down), but as far as I can see there is only one segment. Can an autosegmental theory accommodate this, and if so how?
Similarly, in Vietnamese the hook tone would seem to have three changes of direction in its citation form (up, down, back up a bit). Does that mean that a vowel like the one in khoẻ has to be analysed as having three segments?
I believe the duration of a final sonorant will be greater when it follows a short vowel, as in phẩn, but on first impression it seems clunky to me to say that this difference in length is due to the final consonant having two segments rather than one. Would that be the autosegmental approach?