--- In qalam@yahoogroups.com, "Richard Wordingham" <richard@...>
wrote:

>For example, Lanna
> has all the extra consonants and vowels that Thai has.

Correction: Unlike Thai and Lao, it doesn't modify the Indic <t> to
distinguish /t/ and modern /d/ (formerly preglottalised); instead, it
uses Indic <.d> just as modern Khmer does for implosive /d/ with
series 2 vowels.

Modern Khmer uses Indic <.t> for implosive /d/ with series 1 vowels,
the usual accompaniment of implosive /d/. The Lanna use of <.d> had
been puzzling me, but I think I can now see the reason for its using
<.d> rather than <.t>.

When the is no tone mark, live syllables, i.e. those not ending in an
occlusive, starting with /d/ are pronounced with the same tone as
formerly voiced consonants - the 'low' consonants, corresponding to
Khmer series 2. (Of the three original tones on live syllables, the
one written without a tone mark is naturally the commonest of the
three.)

With a tone mark, live syllables starting with /d/ are pronounced
with the same tone as the formerly voiceless consonants,
corresponding to Khmer series 1. This irregularity is shared by Tai
Khuen, Northern Thai and Lao; Tai Lue pronunces live syllables
starting with /d/ with the same tone as formerly voiceless
consonants. The consonants with this behaviour are called mid
consonants, and Lao (and Siamese) have more of them than Tai Khuen
and Northern Thai.

There are a few words that breach these rules, but they are few and
far between. The problem of representing their tones is resolved by
additional tone marks, analysable as a tone class shifter in New Tai
Lue.

One curiosity is that Siamese pronounces Indic <.d> as /d/ in a few
words of Indic origin, although the normal pronunciation is /th/.

Richard.