In Proto-Modern South Arabian there must have been at least three groups of verbs: 1) verbs with Imperfect, Conjunctive and Preterite forms differing in prefix and stem ablaut as well as ending, 2) verbs with Imperfect and Conjunctive differing in prefix and stem ablaut plus endings (including -an of the Energicus) but Preterite differing probably only by zero ending which could be augmented by Energic -an), 3) verbs with the same ablaut in all the three categories which differed only in endings. The Imperfect with long vowel or a diftong after the first root consonant goes back to originally multiplicative/intensive/causative *qatala/qatila class, a variant of qattala. *Qatala/qatila forms are used in Mehri with plural object like in Akkadian, Classical Arabic and Beja. Alleged 'conative' meaning of the derived *qatala verbs does not exist in MSA at all. Like in Ethiopic there is a separate derived form *aqatala which is causative and multiplicative/intensive. It is better to use the name 'Conjunctive' than 'Subjunctive' in MSA since this form is used also as Jussive. It is not true that MSA Energicus (surviving mainly but not exclusively in conditional clauses) goes back simply to Conjunctive since at least in Jibbali many verbs have Energicus (named 'Conditional' by Johnstone) with a special ablaut which cannot be explained as original umlaut due to the affixation of -Vn. The use of Energic *-an with the original Imperfect, Preterite and Conjunctive is an important isogloss connecting MSA with Sabaic and Minean. MSA Conjunctive has different origin in four groups of verbs: Old Preterite/Jussive yV-qtVl, Old Imperfect yV-qtVl-u, Present yV-qVttVl-u/yV-qatVl-u and Old Subjunctive yV-qtVl-a.
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