was only one voiced series and to explain at the same time later developments in some Indo-European dialects that became Greek, Latin, and Sanskrit, which pointed to some kind of aspiration in the voiced series. Hopper also treated the traditional palatalized and plain velar dichotomy as a velar-uvular contrast, disregarding the typological oddity of a system containing *k' vs *q and *ɢ. Gamkrelidze and Ivanov (1973, 1995:5-70) have posited that both non-ejective series (traditional and ) were fundamentally aspirated ( and , respectively) but had non-aspirated allophones ( and ). According to them, the non-aspirated forms occurred in roots with two non-ejectives because no more than one aspirate could be in the same root. To express the variability of aspiration, Gamkrelidze and Ivanov wrote it with a superscripted h: . Thus, an Indo-European (in which represents any non-ejective stop) might be realized as (attested in Indic and Greek) or as (attested in Latin). In contrast, traditional theory would trace a form attested as both and to an Indo-European . The advantage of the interpretation over the previous is circumventing the typological oddity of the language in having only voiced aspirates by identifying the voiceless non-aspirates of the traditional stop system () as voiceless aspirates (). Postulating the voiceless stops as aspirated finds support in helping to explain Grimm's Law, with these purported now-aspirated stops () evolving into Proto-Germanic . This would also be typologically similar to one of the more notable evolutions from Ancient to Modern Greek (with φ, θ, and χ respectively). Consequences The phonation system proposed by the glottalic theory is common among the world's languages. Moreover, the revised system explains a number of phonological peculiarities in the reconstructed system. The absence of a labial plain voiced stop in the protolanguage now becomes an absence of a labial ejective , proportionally a rather more common state of affairs. The theory also provides a completely-coherent explanation to the patterning of the stop series in roots (Hopper 1973): In many languages that have glottalized consonants, there is a phonetic constraint against two such consonants in the same root. The constraint has been found in many languages of Africa, the Americas, and the Caucasus. In Akkadian, the constraint affected borrowed and inherited roots, and one of the two heterorganic emphatics undergoes dissimilation and appears as a simple (unmarked) consonant, which is known as Geers' law. If the "plain voiced stops" were