The study aims to explore negation in Mehri and provide a historical and theoretical account for the types of negation in Mehri. I begin with a diachronic analysis by adopting the grammaticalization theory and providing several examples illustrating how this process— grammaticalization —is taking place in Mehri. I also discuss the negative existential cycle suggested by Croft (1991) and I find Mehri language to be in Stage B > C. In addition, I propose an account of the negative copula in Mehri after I show examples for the reanalysis of a pronoun as a copula because of the grammaticalization process. I demonstrate how this pronoun ends in the head position of predicate phrase (PredP) and raises to attach to the negative l- /al and forms the negative copula. Regarding the theoretical account, I follow Laka (1994), Van Gelderen, (2011) and argue that a negative particle in bi-partite negative clauses was weakened and changed to Polarity Phrase (PolP). In other words, I assume that the preverbal negative (if any) is in the Tense Phrase (TP) layer, changed to a polarity phrase with a u-negative feature in need of checking by the new negative la, projected above TP. I also provide a morphological account by assuming that the preverbal negative particles are clitics that are picked by the subject or verb movement. This agrees with Chomsky (2001) and Boeckx and Stjepanović (2001) who find that head movement involves morphological components. To account for negation and negative polarity items (NPIs), I argue that NPIs such as nowah ‘never’ and ʃaagtaʕ ‘never’ merge with the negative element la to check the negative feature. Finally, I propose an account of negation associated with coordinates clauses, following van Gelderen (2006) who states “the speaker will only use —e.g., coordinates— for structures where a phrase is necessary” (P.6), similarly, Iassume that grammaticalization is not active in Mehri negative coordinates clauses because they are phrases. For this reason, I suggest a feature named W feature in the coordinate phrase that needs checking by the negative al-/l to form one unit with the following element.