Consider Akkadian bētu vs. Hebrew bayit (בַּיִת) (meaning "house") and Akkadian daltu vs. Hebrew delet (דֶּלֶת) (meaning "door"). Are these endings known outside of Akkadian? If so, when did they disappear? Would they have been present in the language(s) of the Proto-Sinaitic inscriptions?
That Akkadian word-final -u is the Nominative case ending, the other case endings being -a for Accusative and -i for Genitive. Thus, the case forms of the noun bētu 'house' are:
Exactly the same case endings are still present in Literary Arabic (Modern Standard Arabic), although in most spoken Arabic dialects they are lost. The declension of the Arabic noun بَيْتُ (baytu) 'house', in the Construct state where no other suffix follows the case vowel:
Nom.: بَيْتُ (baytu)
Acc.: بَيْتَ (bayta)
Gen.: بَيْتِ (bayti)
As for Hebrew, it has no noun case category whatsoever, hence the absence of the case endings. Hebrew is a Northwest Semitic language. Case endings are found in Northwest Semitic languages in the second millennium BCE, but disappear almost totally afterwards.
So we can see that originally all the Semitic languages used to have case, but the tendency is to get rid of it, which was done in Hebrew first (no cases already in Biblical Hebrew), Arabic dialects lost it after the 7th century. Ge'ez, a dead liturgical South Semitic language (Arabic is also a South Semitic language) has (had) just two cases — unmarked Nominative, ቤት (bet) 'house', and Accusative with the suffix -a, ቤተ (beta), which is the same Accusative suffix as in Akkadian and Arabic.
As for the Proto-Sinaitic, it is definitely problematic to speak about vowels in Semitic consonantal alphabets.
* Sáenz-Badillos, Angel (1993). A History of the Hebrew Language. Cambridge University Press. Pages 36–38,43–44,47–50.
4@user17584 We know almost nothing about the language of the Proto-Sinaitic inscriptions, due to the scarcity of data. And as Yellow Sky mentioned, the inscriptions themselves offer no information about vowels, only consonants. Jun 12, 2020 at 17:17
1@user17584 - If the earliest Proto-Sinaitic inscriptions were really made in the early 2nd millennium BCE, and if their language is really Semitic, it is pretty possible that language did have the case endings, but not necessarily — since we know little about that language, it can well come out to be the first Semitic language to loose those endings, earlier than those inscriptions were made. To put it short, it's all just hypotheses. Jun 12, 2020 at 17:18
2@user17584 We can't say with any certainty what "Hebrew with case endings" would look like, because by the time Hebrew is attested, it had lost them. But if you want to know about different types of case-marking in Proto-Semitic, I'd recommend asking a separate question for that, since it's too elaborate a topic to explain in comments. Jun 12, 2020 at 17:35
1Actually, in Arabic it is (indefinite) baytun, baytan, bayti, (determined) albaytu, albayta, albayta.– fdbJun 12, 2020 at 19:48
1@fdb - I gave the forms in the Construct state where neither the nunation nor the definite article distracts attention from the case vowel suffix. Jun 12, 2020 at 19:51
The ending of the nominative singular -u, -un, -um is visible in Akkadian, Arabic, and Ugaritic. It was probably spoken in other languages (e.g. Ancient South Arabian, Ancient Aramaic), but not visible because of the consonantal script.
It can be noted that this system Sg -u (short), Pl -aw (> long u:) is also attested in Hieroglyphic Egyptian.
2What evidence is there that Hieroglyphic Egyptian had Sg -u (short)? There were no vowels marked in Hieroglyphic Egyptian. Jun 12, 2020 at 23:39
1It can be reconstructed from Coptic words, though it is not an easy job.– user23769Jun 13, 2020 at 6:03
3There are also a very few clay tablets from Tell el Amarna that transcribe Egyptian words in cuneiform, which are helpful for this. Jun 13, 2020 at 17:25
2It should be noted that Egyptian, while an Afro-Asiatic language, is not in the Semitic subfamily. This would be like asking a question about Romance languages and then answering, "Note that in Russian....". It's certainly interesting but not really an answer to the question asked Jun 14, 2020 at 11:36
1Egyptian supports the idea that Semitic -u /-aw is more ancient than Semitic. I never implied that Egyptian was a member of Semitic.– user23769Jun 14, 2020 at 12:43