<p>This study examines the interaction of negation and mood in Afaan Oromoo, a Cushitic language in the Afroasiatic phylum. It focuses on the morphosyntactic features of negation and mood about the perfective and imperfective aspects. The data sources include written web corpora, native speakers of Western (Macha) variety and introspection. In the language, the distinct nature of negation is showcased through morphological negation, negative verbs and lexical elements. This highlights the language’s direct approach to conveying negation within clauses. For mood/modality, the study classifies the types as imperative, interrogative and jussive, which have different inflectional properties. Furthermore, it reveals the use of modal auxiliaries, such as <i>k’aba</i> ‘should be’, <i>taɁa</i> ‘could be’, <i>taɁinnaa</i> ‘may become’, <i>laata</i> ‘may be’, <i>dandaɁa</i> ‘can/be able’, mala ‘must be’, etc., in the expression of modality in everyday practice. The study has great contribution to the fields of language documentation, typological studies, and theoretical linguistics, serving as a critical resource for scholars, educators and language enthusiasts interested in the exploration and preservation of Afaan Oromoo. The study shows that certain negated structures involving double negation trigger mitigated interpretations and may influence processing complexity. This contributes to debates on how languages encode polarity and modality, and how such systems impact cognitive processing and language comprehension.</p>