One thing in these discussions that's really only been alluded to is the
grammatical uses of ablaut. The ablaut displayed in the English strong verb
sing/sang/sung is grammatical.
At 5.3.6 in the 96 edition, Szemerényi writes:
Vowel gradation has a function in the Indo-European grammatical system
the importance of which cannot be overstated. In the verb system, for example,
full grade is for the most part associated with the present tense, zero grade
with the aorist, and o-grade with the perfect
Earlier on, at 5.3.2, he says
The monosyllabic short-vowel ablaut series came to be of unique
importance in Germanic. They form the foundation and framework for five of the
seven classes of the so-called strong verbs, which survive with extraordinary
tenacity right through to the modern Germanic languages.
Szemerényi speaks of noun ablaut at 126.96.36.199:
Originally ablaut alternations occured quite generally in the stem.
Basically the full grade had its place in nom. voc. acc. loc. s. and nom. voc.
acc pl. (strong cases), often with long grade in the nom s. of animate stems;
in the other cases there appears basically the zero grade (weak cases). For
example, *dónt-m 'tooth' (acc. s.) but *dnt-ós
(gen. s.) but *dnt-sú (loc. pl.). Where the zero
grade caused our would have cause difficult consonant groups, the vowel was
either not lost at all or soon restored. In the case of *ped- 'foot', for
example, the gen. s. *pd-ós (i.e. *bdós) was
hardly in use for very long.
It is only in very rare cases that a paradigm 'torn apart' by ablaut is
preserved, or at least fragmentarily.
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