East Semitic languages stand apart from other Semitic languages, which are traditionally called West Semitic, in a number of respects. Historically, it is believed that the linguistic situation came about as speakers of East Semitic languages wandered further east, settling in Mesopotamia during the 3rd millennium BC, as attested by Akkadian texts from this period. By the early 2nd millennium BC, East Semitic languages, in particular Akkadian, had come to dominate the region.
Modern understanding of the phonology of East Semitic languages can be derived only from careful study of written texts and comparison with the reconstructedProto-Semitic. Most striking is the reduction of the inventory of back consonants, the velar and pharyngealfricatives, as well as glottals. Akkadian preserves *ḫ and (partly) *ḥ only as a single phoneme transcribed ḫ and usually reconstructed as a voiceless velar or uvular fricative. All of the sounds *ʾ, *h, *ʿ, *ġ have been lost. Their elision appears to give rise to the presence of an e vowel where it is not found in other Semitic languages (for example, Akk.bēl 'master' < PS.*ba‘al). It also appears that the series of interdental fricatives became sibilants (for example, Akk.šalšu 'three' < PS.*ṯalaṯ). However, the exact phonological makeup of the languages is not fully known, and the absence of features may have been the result of the inadequacies of Sumerian orthography to describe the sounds of Semitic languages, rather than their real absence.
Huehnergard, J. (1995). "Semitic Languages". In Sasson, Jack (ed.). Civilizations of the Ancient Near East. New York. pp.2117–2134.{{cite book}}: CS1 maint: location missing publisher (link)
