From Old European
Today, the reconstruction of consonantal sounds to explain what was reconstructed before as uncertain vocalic schwa indogermanicum or schwa primum is firmly accepted in Indo-European (IE) studies in general, and there is a general agreement on where laryngeals should be reconstructed[Keiler 1970].
Even the number and quality of those laryngeals is today a field of common agreement, although alternative number of laryngeals and proposals for their actual phonemic value do actually exist. Reconstructed laryngeals are valid only for the oldest reconstructible stage using comparative grammar, i.e. Middle Proto-Indo-European or Proto-Indo-Hittite[Kloekhorst 2016][Schmidt 2011][Jasanoff 2003], and potentially also Indo-Uralic[Hyllested 2009][Kloekhorst 2008].
These laryngeals are in most cases notated as *h₁, *h₂, *h₃ but sometimes also with their assumed realization *ha, *he, *ho, or phonetic inventory, *ʔ/*h, *χ, *ʕʷ. A more traditional representation is found in *a₁, *a₂, *a₃, or *ə₁, *ə₂, *ə₃. Sometimes, a vocalic quality is assumed, *Ae, *Ee, *Oe.
Their evolution during Late Proto-Indo-European (LIE), after the separation of Anatolian, is often assumed as a loss or deletion with certain common outputs in the daughter branches or proto-languages[Adrados 1998][Bomhard 2015][Koch 2013]. However, it has also been stated that the three laryngeals might have survived until the final phase of LIE[Rasmussen 1999]. A certain support is found for the survival of laryngeals until after the separation[Cogwill 1960], but the general view is that they disappeared completely, leaving only indirect traces in historical languages[Sanker 2015].
As Clackson[Clackson 2007] sums up: “Particularly puzzling is the paradox that laryngeals are lost nearly everywhere, in ways that are strikingly similar, yet apparently unique to each language branch. We can of course assume some common developments already within PIE, such as the effect of the laryngeals *h₂ and *h₃ to change a neighbouring *e to *a or *o, but the actual loss of laryngeals must be assumed to have taken place separately after the break-up of the parent language (…) it would have seemed a plausible assumption that the retention of *h₂, and possibly also *h₁ and *h₃, is an archaism of Anatolian, and the loss of the laryngeals was made in common by the other languages.”
Chronologically, there is no commonly agreed scheme as to the maintenance of laryngeals in daughter languages. Whereas there is some common ground whereby laryngeals were lost by the time when Late Indo-European languages were written down[Rasmussen 1999][Sukač 2014], its survival has been supported for certain late proto-languages, e.g. for Slavic as late as Charlemagne’s times[Kortlandt 1975].
- [Adrados 1998] ^ Adrados, F.R. 1998. La reconstrucción del indoeuropeo y de su diferenciación dialectal. In Manual de lingüística indoeuropea, edited by F. R. Adrados, A. Bernabé and J. Mendoza. Madrid: Ediciones clásicas.
- [Bomhard 2015] ^ Bomhard, Allan R. 2015. A Comprehensive Introduction to Nostratic Comparative Linguistics. With special reference to Indo-European. Second revised, corrected and expanded edition (as of May 2017) ed. 4 vols. Vol. 1. Charleston, SC.
- [Clackson 2007] ^ Clackson, James. 2007. Indo-European Linguistics. An Introduction. Cambridge: Cambridge University Press.
- [Cogwill 1960] ^ Cogwill, Warren. 1960. Greek ou and Armenian oč. Language 36 (3):347-350.
- [Hyllested 2009] ^ Hyllested, Adam. 2009. Internal reconstruction vs. external comparison: the case of the Indo-Uralic larnygeals. In Internal reconstruction in Indo-European: Methods, results and problems. Section papers from the XVIth International Conference on Historical Linguistics held at the University of Copenhagen, edited by J. E. Rasmussen and T. Olander. Copenhagen: Museum Tusculanum.
- [Jasanoff 2003] ^ Jasanoff, Jay H. 2003. Hittite and the Indo-European Verb. Oxford, New York: Oxford University Press.
- [Joseph 2000] ^ Joseph, B. D. 2000. Hittite andurza “inside, indoors” and the Indo-Hittite Hypothesis. In The Asia Minor Connexon: Studies on the Pre-Greek Languages in Memory of Charles Carter, edited by Y. L. Arbeitman. Chicago: Peeters Publishers.
- [Kazaryan 2017] ^ Kazaryan, V. K. 2017. The Tense/Aspect system of the Indo-European verb and the Indo-Hittite hypothesis. Paper read at Indo-European Linguistics and Classical Philology - XXI Proceedings of the 21st Conference in Memory of Professor Joseph M. Tronsky, 26–28 June, 2017, at St. Petersburg.
- [Keiler 1970] ^ Keiler, Allan R. 1970. A phonological study of the Indo-European laryngeals. Edited by C. H. van Schooneveld. Vol. 76, Janua Linguarum. Studia memoriae Nicolai van Wijk dedicata. The Hague / Paris: Mouton.
- [Kloekhorst 2008] ^ Kloekhorst, Alwin. 2008. Some Indo-Uralic Aspects of Hittite. JIES 36 (1 & 2).
- [Kloekhorst 2016] ^ Kloekhorst, Alwin. 2016. The Anatolian stop system and the Indo-Hittite hypothesis. In Indogermanische Forschungen.
- [Koch 2013] ^ Koch, John T. 2013. Out of the flow and ebb of the European Bronze Age: Heroes, Tartessos, and Celtic. In Celtic From the West 2: Rethinking the Bronze Age and the Arrival of Indo-European in Atlantic Europe, edited by J. T. Koch and B. Cunliffe. Oxford: Oxbow Books.
- [Kortlandt 1975] ^ Kortlandt, Frederik. 1975. Slavic Accentuation. A Study in Relative Chronology. Lisse / Netherlands: The Peter de Ridder Press.
- [Rasmussen 1999] ^ 1 2 Rasmussen, E. J. . 1999. Selected Papers on Indo-European Linguistics: With a Selection on Comparative Eskimo. Vol. 1, Copenhagen Studies in Indo-European. Copenhagen: Museum Tusculanum Press.
- [Sanker 2015] ^ Sanker, Chelsea. 2015. Phonetic Features of the PIE “Laryngeals”: Evidence from Misperception Data of Modern Gutturals. In UCLA Indo-European Conference, 27th Annual Meeting. Los Angeles, California.
- [Schmidt 2011] ^ Schmidt, Karl Horst. 2011. Contributions from new data to the reconstruction of the proto-language. In Reconstructing Languages and Cultures, edited by E. C. Polomé and W. Winter. Berlin, Boston: De Gruyter Mouton.
- [Sturtevant 1942] ^ Sturtevant, Edgar Howard. 1942. The Indo-Hittite Laryngeals. Harvard: Linguistic society of America.
- [Sukač 2014] ^ Sukač, Roman. 2014. Introduction to Proto-Indo-European and Balto-Slavic Accentology. Newcastle upon Tyne: Cambridge Scholars Publishing.