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Patrick:
I thought it might be helpful to delineate my assumptions concisely.
1. The earliest prevalent PIE root-form was *CACA, where *A is the
Ablaut-vowel, which can appear as *é/*o/*Ø.
2. The singular/punctual is expressed by penultimate stress-accentuation:
*CÁCA > *CéCA.
3. The earliest expression of stress-unaccented *A was *Ø: *CéCØ.
4. The plural/durative is expressed by ultimate stress-accentuation: *CACÁ
> *CØCé.
a. Any *e is the result of present or former
stress-accented *A.
5. The _next_ earliest expression of stress-_de_-accented *é was *o;
*CéCØ with ultimate stress-accentuation becomes *CoCé.
a. The origin of *o may have originally been purely
epenthetic.
6. In the _last_ earliest stage, stress-accentuation shifts do not occasion
deletion or quality change of vowels.
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