Natural languages go through two major cycles in their diachronic change. A high synthetic marking characterizes the first cycle, and a high analytic marking characterizes the second. This thesis investigates an emerging analytic passive in Modern Standard Arabic (MSA), representing the analytic cycle. This construction is designated periphrastic passive since two grammatical morphemes mark the passiveness. The older morphological passive construction in Classical Arabic (CA) and MSA, representing the synthetic cycle, is juxtaposed with the periphrastic passive. Given the inconsistent passive characterization in the literature, the comparison between the two passive forms is couched in the prototypical passive analysis. This thesis seeks to show that the periphrastic passive in MSA has grammaticalized to perform the passive function. It argues that the main verb in the periphrastic passive, i.e., tamma/yatimmu, has grammaticalized to a passive auxiliary. The corpus data of CA and MSA about tamma/yatimmu complementation, the subjectverb agreement, and the frequency of tamma/yatimmu show the grammaticalization of the periphrastic passive. The lexical source of the auxiliary tamma/yatimmu, i.e., ‘finish,’ is also attested to perform the passive function in Colloquial Icelandic (CI). The commonality between the lexical sources in the two passive constructions in MSA and CI suggests that the lexical source ‘finish’ could serve as a lexical source of passive constructions.