A question that has driven much of the current research in formal syntax is whether it is the lexicon or the syntax that determines the argument structure of a verb. This dissertation attempts to answer this question with a focus on Arabic, a language that has received little attention in the literature of argument structure. In this dissertation, argument structure realization is examined in relation to three different components, namely the root, the CV-skeleton and the structure around the verb. I argue that argument structure is not determined on a root level in Arabic. I also show that only few CV-skeletons (verb patterns) are associated with certain argument structures. Instead, the burden of determining argument structure lies on elements around the structure of VP. The determinants of inner aspect in Arabic and the relation between eventuality types and argument structure are also examined. A cartographic model is provided to show how elements around the VP play a role in determining the inner aspect. This model also represents a relationship between argument structure and eventuality types. The question of what determines argument structure is further addressed through the investigation of the causative/inchoative alternation in Arabic in light of recent semantic and syntactic accounts. I argue that most Arabic verbs that undergo the alternation are non-agentive change-of-state verbs. Although certain lexical characteristics may account for which verbs alternate and which do not, exceptions within a language and/or across languages do exist. I point to a range of phenomena that can be only explained from syntactic points of view.