One step back to look at the general picture.
I have said that the BS accent system goes back to a
simplified PIE system, with the following accentual
paradigms:
athematic: barytonic / mobile
thematic : barytonic / oxytonic (mesotonic)
The essential innovation in Balto-Slavic was the extension
of mobility to the thematic declensions/conjugations.
In the nouns/adjectives, the driving force was the barytonic
accentuation of the accusative. The oxytonic thematics
became mobile because they _could_ retract the accent in the
accusative (*draugám, *draugó:ns -> *dráugam, *dráugo:ns).
The result was a system with barytonic (a.p. a) and mobile
(a.p. c) stems. Only the neuter o-stem nouns remained
oxytonic (a.p. b).
In the verb, the developments were different. It was the
_barytonic_ thematic verbs which become mobile. Given the
paradigms:
ath. bar. ath. mob. them. bar. them. oxy.
*bódmi *ésmi *béro: *be:gnó:
*bódsi *ési *béresi *be:gnési
*bództi *ésti *béreti *be:gnéti
*bódmes *esmés *béremes *be:gnémes
*bództes *estés *béretes *be:gnétes
*bódn.ti *sónti *béronti *be:gnónti,
it is likely that the trigger for the shift of barytonic
thematics to mobile accentuation was the plural (béremes,
béretes, béronti > beremés, beretés, berónti [later:
berontí]). Epecially if the 3pl. had at first not yet
shifted to lateral mobility, it is clear that for the
oxytonic thematic verbs, there was less reason to shift to
mobility, which is why they remained a.p. b. In the verb,
the three pre-BS accentual paradigms remained: a.p. a (ath.
bar.), a.p. b (them. oxy.) and a.p. c (ath. mob. + them.
bar.). The barytones must have formed only a very small
category, but they were "saved" by Hirt's law.
=======================
Miguel Carrasquer Vidal
mcv@...