Much recent work investigates the role of syntax in regulating the distribution of φ-morphology (person, number and gender) in the nominal and clausal domains. Two main ideas are that the syntactic structure that introduces φ-categories in the two domains shows some degree of parallelism and that syntactic processes of agreement and cliticization affect the realization of φ-morphology. Here, the most fine-grained analysis of Classical Arabic φ-morphology to date reveals two strong parallels between the φ-morphology of nouns and verbs: (i) the same morphs are used on both, and (ii) these morphs appear in the same order. The parallels break down in third person: There are third person morphs on pronouns, but not on verbs. While (i) and (ii) are explained by syntactic parallelism, the status of third person is illuminated by the alternation between suffixal and prefixal person-morphology in perfective vs imperfective aspect. First and second person morphs can appear as prefixes or suffixes because they are clitics that are undergoing movement. A comparison of person morphs in pronouns indicates that third person morphs are not clitics, explaining their absence on verbs. These little analyzed data in Classical Arabic reveal a diversity of morphosyntactic processes in what might informally be called agreement.
