This paper has a two-fold goal. First, it attempts to argue that the circumfixal nature of the negative morpheme in Moroccan Arabic supports the existence of impenetrable (cyclic) domains, as in Chomsky’s (2001) Derivation by Phase. The second goal is to propose a principled account of the long-standing puzzle of the co-occurrence restriction holding between the post-verbal negative marker {-ʃ} and negative polarity items in an adjacent domain. Applying the precepts of Distributed Morphology, my proposal consists of formalizing this restriction in the form of a
general constraint banning the realization of multiple negative morphemes in the same spell-out domain, with the effects being the deletion of the post-verbal negative marker. This is achieved via postulating post-syntactic morphological operations. I show that this prediction is not only borne