It consists of the clearly defined sub-groups: Modern South Arabian, Old South Arabian, Ethiopic, Arabic, and Northwest Semitic (this including Hebrew, Aramaic, and the extinct Amorite and Ugaritic languages).
Ethiopic and South Arabian show particular common features, and are often grouped together as South Semitic. The proper classification of Arabic with respect to other Semitic languages is debated. In older classifications, it is grouped with the South Semitic languages. However, Hetzron and Huehnergard connect it more closely with the Northwest Semitic languages, to form Central Semitic. Some Semiticists continue to argue for the older classification, based on the distinctive feature of broken plurals. Some linguists also argue that Eteocypriot was a Northwest Semitic language spoken in ancient Cyprus.
P. Haupt (1878) first recognized that the qatala past tense found in West Semitic was an innovation, and that the Akkadian prefixed past tense must be archaic. It was F. Hommel, however, who recognized the implications of this for the subgrouping of Semitic; cf. Hommel(1883: 63, 442; 1892: 92-97; 1926: 75-82).