In my previous post, I explained that I recently pondered on how Syncope would have affected inanimate thematic noun stems. If I'm right that many animate thematic stems in Mid Indo-European (MIE) were preserved by resisting Syncope due to phonotactic reasons such as avoiding awkward syllable codae, then one should expect that inanimate thematic stems should have behaved similarly.
After pondering on a potential Semitic loan *qárnu "horn" and its likely path of borrowing into PIE, I came to the conclusion that inanimate thematic nouns indeed did survive into early Late IE (eLIE) but that they were endingless in the nominative and accusative. This means that this would have resulted in wordforms such as *kérnə "horn" in the nomino-accusative. I fleetingly mentioned at the end of my last post that if these stems had survived unmolested, Indo-Europeanists would be speaking of *e-stems (i.e. **kérne). Instead however, this thematic stem appears to be reconstructed as *krnóm. This and other inanimate thematic stems exhibit interesting effects such as the curious disappearance of *m in the locative case (e.g. *yugóm "a yoke" but *yugó-i "among a yoke") which leads many to assume that this was a functional ending rather than the product of misanalysis and missegmentation by early Indo-European speakers. So I take it that these endingless stems must have been converted by adding the genitive ending *-óm by analogy with inanimate thematic adjectives but were reanalysed as thematics ending in *-ó- with a pseudo-ending *-m in the nominative and accusative cases. I don't think that the final nasal stop had anything to do with the accusative case ending which was restricted to the animate stems anyway.
Yet, if these stems were "converted", surely the process wasn't entirely complete, was it? Could there be still some evidence of bare thematic stems in the language that failed to be converted? So now I'm starting to wonder whether this might explain the curious shape of the numeral *pénkʷe "5". If this numeral had been originally treated as a collective inanimate noun in Mid IE, its failure to be converted would be natural if it came to be solely understood as a numeral rather than a generic noun. Thus MIE *kérna "horn" > eLIE *kérnə > *kr̥n-ám (conversion) > *ḱr̥nó-m (missegmentation) yet MIE *pénkʷa > eLIE *pénkʷə > *pénkʷe (no conversion in numerals). Word-final schwa in early Late IE is expected to become PIE *-e# since it only becomes *-o- word-medially in the presence of a following voiced segment and this then explains the thematic vocative case which ends in *-e (i.e. the vocative case was endingless causing this Pre-IE schwa to be word-final).