Pronominal Clitic System in the Course of Persian History and the Causes of its Change

«Syntactic change should not arise، unless it can be shown to be caused» (Longobardi، 2001:278). Historically placed in second position of the clause، Persian Pronominal Clitics behave differently today and appear in three different structural-typological patterns: a) preposition + clitic assigned oblique case; b) nominal + clitic assigned genitive case; and c) immediate adjacency of a transitive verb assigned accusative case. Aiming to discover the causes of Persian''s achievement to this trio of patterns، this study was conducted in the framework of Generative Grammar. The diachronic analysis shows that a sequence of some factors has been involved in changing Persian’s historical second position Clitic System: firstly، some morphological changes and the speaker’s attempt to remove the ambiguities have paved the ground for other structural changes to happen. Secondly، after particular morphological feedings، patterns a & b have been established as a result of analogical generalization of pre-existing linguistic structures. Pattern c has gradually come to existence by frequently reanalyzing the position of clitics in the sentence. This pattern can be a part of the grammaticalization process of Persian clitics that has been accelerated by morphological changes and Reanalysis. As a final step، linguistic contact to Arabic was recognized as an accelerating factor in applying this trio of patterns in Persian Standard Language.