"Mark J. Reed" <[log in to unmask]> writes:
> Quick terminology question:
> I thought umlaut was a specific variety of ablaut - a consistent featural
> change.

Hmm, ablaut is a quite arbitrary shift of the stem vowel (at least
today).  I don't know what motivated it, but probably very ancient
phonology rules that inserted two different parenthetic vowels like in
Old Greek (e vs. o vs. consonantal stem variants).

Umlaut is newer.  Some kind of phonological harmony.  E.g. the German
umlaut is an i-umlaut technically as it shifted all preceding vowels
of the word to the front in front of an /i/ in an appended ending.

> But it doesn't seem to be; in German, for instance, while umlaut
> does always move a vowel from back to front,

Right.  In ancient times this happend because there was an /i/
following the umlauted vowels.

> it has an inconsistent effect on the height:  [e] is higher than a
> [A];  [9] is lower than o [o], while  [y] is the same height as u.
> Is there some other consistency here that I'm missing?

In Modern German the umlaut effect is lexicalised since the former
endings that contained the trigger /i/ have vanished or changed to
different vowels.  Further, I suspect that the vowels have shifted a
bit after umlauts first occured.  (BTW, the umlaut in German is
only uneven in /a/:

Regular umlaut by simple fronting:
     /u:/ -> /y:/
     /U/  -> /Y/
     /o:/ -> /2:/
     /O/  -> /9/

Shifted in Modern German:
     /a:/ -> /E:/
     /a/  -> /E/

If you have a look at Icelandic, the effect is more overt (more /i/s
are still visible), while many things are also lexicalised now.  To
see the effect, you have to look at Proto-(West?)Nordic (the
reconstructed ancester of Old-Westnordic).  (I don't know when this
effect happened to German).

> Is the effect perhaps consistent for a given vowel across languages
> that exhibit umlaut?

Well, i-umlaut occurs in quite the some form in Old Westnordic (Old
Icelandic).  Old Westnordic also has u-umlauts that result on a change
of /a/ to /2/ (at least) in Modern Icelandic.  For whatever reason. :-)