preterite-tense formation (yajlis-) into a present tense. The elimination of other prefix-conjugated mood/aspect forms (e.g., a present tense formed by doubling the middle root, a perfect formed by infixing a after the first root consonant, probably a jussive formed by a stress shift) in favor of new moods formed by endings attached to the prefix-conjugation forms (e.g., -u for indicative, -a for subjunctive, no ending for jussive, -an or -anna for energetic). The development of an internal passive. There are several features which Classical Arabic, the modern Arabic varieties, as well as the Safaitic and Hismaic inscriptions share which are unattested in any other Central Semitic language variety, including the Dadanitic and Taymanitic languages of the northern Hejaz. These features are evidence of common descent from a hypothetical ancestor, Proto-Arabic. The following features can be reconstructed with confidence for Proto-Arabic: negative particles * ; * to Classical Arabic G-passive participle prepositions and adverbs , , , , a subjunctive in - -demonstratives leveling of the - allomorph of the feminine ending complementizer and subordinator the use of - to introduce modal clauses independent object pronoun in vestiges of nunation On the other hand, several Arabic varieties are closer to other Semitic languages and maintain features not found in Classical Arabic, indicating that these varieties cannot have developed from Classical Arabic. Thus, Arabic vernaculars do not descend from Classical Arabic: Classical Arabic is a sister language rather than their direct ancestor. History Old Arabic Arabia boasted a wide variety of Semitic languages in antiquity. In the southwest, various Central Semitic languages both belonging to and outside of the Ancient South Arabian family (e.g. Southern Thamudic) were spoken. It is also believed that the ancestors of the Modern South Arabian languages (non-Central Semitic languages) were also spoken in southern Arabia at this time. To the north, in the oases of northern Hejaz, Dadanitic and Taymanitic held some prestige as inscriptional languages. In and parts of western Arabia, a language known to scholars as Thamudic C is attested. In eastern Arabia, inscriptions in a script derived from ASA attest to a language known as Hasaitic. Finally, on the northwestern frontier of Arabia, various languages known to scholars as Thamudic B, Thamudic D, Safaitic, and Hismaic are attested. The last two share important isoglosses with later forms of Arabic, leading scholars to theorize that Safaitic and Hismaic are in fact early forms of Arabic