This monograph presents a morpho-syntactic investigation on modality, aspect, and negation by concentrating on Persian, and is designed to contribute to theoretical linguistics and the study of Iranian languages. The analysis is based on the Minimalist program. This research challenges the idea that the syntactic structure maps on the semantic interpretation or vice versa. The discussion presented in this monograph shows that the syntactic structure of Persian modals is uniform no matter if the modals are interpreted as having root or epistemic readings. Although it is claimed that modals are raising constructions in different languages, modals in Persian, which does not have subject-raising constructions, show a different syntactic behavior. Furthermore, the structural analysis of the interaction of Persian modals and negation shows that because of the scope interaction of negation and modals, the syntactic structure of modals with respect to negation mostly corresponds to the semantic interpretation of modals.