Exu:
> However, -i is (as far as I know) a final vowel when used as a tense
> marker, and hence can not be a thematic vowel in the commonly used
> sense.
It depends on how you mean. It does appear that we have *i-stems as
alternates of *o-stems (the 'thematic stems') for whatever reason. In
that sense, *i-stems might be said to be another kind of thematic stem.
Of course 'thematic stems' are being used untraditionally here in a
sense more sensitive to the apparent etymology of these items and you're
correct that thematic stems are normally of the alternating-*e/*o kind.
However, considering that the thematic vocative in *-e would appear to
show a reflex of the thematic vowel in final position, your criterion
doesn't distinguish these *i-stems from the thematic stems alternating
between *-e- and *-o-.
= gLeN