While early linguists such as André Martinet and Morris Swadesh had seen the potential of substituting glottalic sounds for the supposed plain voiced stops of Proto-Indo-European, the proposal remained speculative until it was fully fleshed out simultaneously but independently in theories in 1973 by Paul Hopper of the United States[2] and by Tamaz V. Gamkrelidze and Vyacheslav Ivanov of the Soviet Union in the journal Phonetica in 1973.
"[3] The most recent publication supporting it is Allan R. Bomhard (2008 and 2011) in a discussion of the controversial Nostratic hypothesis, and its most vocal proponents today are historical linguists at the University of Leiden.
In the original Proto-Indo-European proposal, there was a fourth phonation series, voiceless aspirated *pʰ, *tʰ, *ḱʰ, *kʰ, *kʷʰ, which was assumed to exist on the basis of what is found in Sanskrit, which was then thought to be the most conservative Indo-European language.
However, it was later realized that the series was unnecessary and that it was generally the result of a sequence of a tenuis stop (*p, *t, *k, *ḱ, *kʷ) and one of the Proto-Indo-European laryngeal consonants: *h₁, *h₂, or *h₃.
Thirdly, a longstanding but unexplained observation of Indo-Europeanists about the distribution of stops in word roots is that it had long been noted that certain combinations of consonants were not represented in Proto-Indo-European words in terms of the traditional system: The constraints on the phonological structure of the root cannot be explained in terms of a theory of unlimited assimilation or dissimilation since they display a radical difference in patterning between three sets of consonants, the stops, that ought to behave identically.
The glottalic theory proposes different phonetic values for the stop inventory of Proto-Indo-European:[6] In his version of the glottalic theory, Hopper (1973) also proposed that the aspiration that had been assumed for the voiced stops *bʰ *dʰ *gʰ could be accounted for by a low-level phonetic feature known to phoneticians as "breathy voice".
Kortlandt also proposes word-final glottalization in English to be a retention and derives features such as preaspiration in Icelandic and Faroese and sporadically in Norwegian and certain instances of gemination in Swedish and High German from preglottalization as well.
The primary objection to the theory is the alleged difficulty in explaining how the sound systems of the attested dialects were derived from a parent language in the above form.
Taking them as identical but independent innovations would, according to traditional models of sound change, be an astonishing coincidence, and one which most linguists would find very hard to believe—ejectives tend to be quite stable, diachronically.
[16] However, this could be explained if it is assumed that—rather than Proto-Indo-European possessing broad uniformity—a putative shift from ejective to voiced stops was already present as variation at an early stage.
[17]) A compromise viewpoint would be to see the original formulation of glottalic theory, with ejective stops, as representing an earlier stage in the history of Proto-Indo-European, which would have undergone a period of internal evolution into a stage featuring unstable voiced glottalized stops, or even into the similarly unstable traditional system, before it branched out into the daughter languages.
One objection that has been raised against the glottalic theory is that the voiced stops are voiceless in some daughter languages: "unvoiced" in Tocharian and Anatolian and aspirates (later fricatives) in Greek and Italic.
That is based on the "voiced" series triggering length in preceding vowels in daughter languages, the glottalic closure before the stop acting in a manner akin to the laryngeals.
In other words, Kümmel has circled back to an exoticized version of one of the secondary characteristics of the traditional model the original glottalic theorists had objected to.
Nevertheless, proponents of a revised model like Weiss (2009) acknowledge the rarity of bilabial implosives, suggesting that they became *w before consonants, citing the strongest reconstructed roots containing *b (from pre-PIE [ɓ]) were pre-vocalic like *bel- "strong" and *bak- "stick" in contrast to the preponderence of PIE *wr-, *wl-.
That, he argues, is typologically more common than voiced aspirates without voiceless counterparts:[28] Schirru has also suggested that the voiced aspirated stops could be better analyzed as having the feature [+slack vocal folds] or [−stiff vocal folds]:[30] As mentioned above in "Direct and indirect evidence", Frederik Kortlandt in particular has argued for these traces of glottalization being found in a number of attested Indo-European languages or the assumption of glottalization explaining previously known phenomena, which lends the theory empirical support: Arguably, the minority status of most of the languages which provide the allegedly-certain direct evidence for the theory may be a rather large problem.[why?]
If Proto-Indo-European once showed glottalization, this circumvents the dispute by not requiring the assumption that we are dealing with an example of a sound law that affects deep phonological structure.
There is direct evidence for the traditional murmured series originating as an allophonic variation in the behavior of the voiceless stops in English and German, where they emerge as aspriates except after /s/ and especially to only word-initially.
Kortlandt follows this proposal, but also follows more recent versions of the theory in having no voiced consonants or treating voicing as non-distinctive, proposing that the pulmonic stops had phonemic length like vowels had:[10] It seems paradoxical for Kortlandt to posit that, on the one hand, there are daughter languages of Proto-Indo-European where certain instances of gemination are indirect evidence of former instances of glottalization, and on the other hand, gemination was already phonemic in Proto-Indo-European.
The solution to this seeming paradox is that Kortlandt is describing a stage of Proto-Indo-European after an original allophonic variation between glottalic and geminated pulmonic stops became phonemic.
The reason for this is that the mountain-dwelling Proto-Uralic people who would have migrated to what is presumed to have been the Proto-Indo-European homeland would have found the Caucasus Mountains a comfortable place to resettle, being similar to their home.
[dubious – discuss] This resettlement brought the Proto-Uralic people into contact with Proto-Caucasian languages, from which they borrowed ejectives, as allophones of which they subsequently innovated the geminated pulmonic stops.
If voiced aspirates ever existed at an ancient stage of any Indo-European languages other than Indic, they could have easily become fricatives either phonemically, as in Italic and ultimately in Greek, or allophonically, as in Germanic.
This direct evidence for the ease of occurrence for such a development renders Kortlandt's view that the two voiced series must have, however partially, collapsed back into one, in Albanian and Iranian[37] something of a paradox.
The paradox goes even deeper, many apparent instances of preglottalized stops in Kortlandt's view of late Proto-Indo-European may have been the result of a metathesis 'V/ʔV→V'/Vʔ equally to C'/Cʔ→'C/ʔC.