The Optative negative of Beja is a multifunctional paradigm which encodes optative, hortative and jussive grammatical meanings, depending on the person, as well as participant-internal and participant-external modalities of impossibility and unnecessity. It is also the sole paradigm licensed in balanced embedded clauses. Based on a large corpus of naturalistic first-hand data, this study analyses the various uses of the paradigm, provides an account of its evolution from the premodal stage to the post-modal stage on the basis of language internal morpho-syntactic cues, and proposes a diachronic semantic map, based on van der Auwera and Plungian (1998) model. It shows that semantic maps are not only useful for typological purposes, but also for language internal studies, helping understand the semantic shifts that occurred in the grammar of unwritten languages with no recorded history.