The verbal system of Beja, the sole North-Cushitic language, possesses several indicative and modal verb paradigms whose precise semantic values and syntactic uses are still ill-known. The fact that almost each linguist developed its own terminology (with fortunately some commonalities), does not help clarify the situation and the analyses are often different and controversial for some TAM. This paper focuses on one of the Beja paradigms, the so-called Optative, as labeled by Roper(1928), in its negative form on the basis of spontaneous narrative data that I recorded in Sinkat (Sudan) between 2004 and 2007. Their analysis, which confirmed in their great lines previous studies, nevertheless brought to light particular syntactic uses and modal values of capacity and necessity that have never been mentioned before. Section 2 presents a brief overview of the main Indicative (2.1) and Mood (2.2) paradigms in order to give the reader the basic knowledge required to better understand the morphology and the semantics of the Optative within the verbal system. Section 3 is dedicated to the analysis of the Optative Negative as an optative in independent clauses (3.1), as a dependent verb form in relative (3.2), completive (3.3) and conditional (3.4) clauses, and as a modality marker of capacity and necessity in exclamatory utterances (3.5). Section 4 proposes a tentative semantic map of the Optative Negative.