Re: Three vowel grades

To get you thinking outside of Indo-European languages, here is the
inventory of tones in Mandarin Chinese:

Peking Mandarin has only four contrastive tones.  In general, Mandarin
dialects have fewer tones than non-Mandarin dialects spoken in South China.
The first tone is the level, relatively high tone.  The second is a high
rising tone; it starts somewhat below the register of the first tone and
rises in pitch to the level of the first tone.  The third is a relatively
low falling-rising tone, and the fourth is a high falling tone.  The first
and third tones are also relatively longer in duration than the other two.

The so-called neutral tone which appears in some weakly stressed syllables
(usually on the second syllable of a compound word or disyllabic morpheme)
is realised in different ways depending on the tone of the preceding
syllabe.  In general it is realised as a short, level (or nearly so) tone
which is mid to low in register.

A tone three syllable preceding another tone three syllable changes its
tone to tone two, but this change (called tone sandhi) is contrained by
syntactic considerations such as whether the two syllables in question are
immediate constituents.  Tone three before a syllable with tone other than
three loses its rising portion.

Note that high vowels [i], [y] (a high front rounded vowel), and [u] when
not preceded by a consonant are pronounced with an initial homorganic glide.

Thus, Mandarin Chinese has many vowels, about 35.  Their romanised phonetic
representations are as follows:

i
in
ian
iang
ing
ie
iu
iao
ia

u
un
uan
uang
ong
uo
ua
uai
ui

Ü
un
uan
iong
ue,ÜE

a
an
ang
ao
ai

e
en
eng
ei
er

o
ou

I couldn't post the symbols.  I recommend checking out the sketches of this
language, Mandarin Chinese, and others in "An Introduction to the Languages
of the World".  It's a book, but I forget who wrote it.  It's not very big.

I hope this helps a bit.

--a.i