In Indo-European languages with mobile paradigmatic accent, fixed oxytones and movable athematic stems are accented by the same rule. When applied to syllables as accentual units, this rule generates the Sanskrit accent patterns. When applied to moras, it generates the Greek accent patterns—including, as a special case of mobility, the paradigmatic alternation of acute and circumflex. A modification of the the same rule accounts for the extension of mobility to originally oxytone - o - and - ā -stems in Bal to-Slavic, and for the rise of the Balto-Slavic acute and circumflex accents.
Paul Kiparsky (Sat,) studied this question.
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