In this article, the behavior of pronominal clinics in Middle and Modern Persian as well as the historical change in their placement in the clause/ sentence is studied. In Middle Persian, the clitics obey the second-position system, and they always appear as the second constituent of the clause/ sentence. In Classical Modern Persian this system is reserved, although there are some changes in the system, including disappearance of the phenomenon of discontinuous constituency and also skipping over some constituents when determining the second-position. But, in this language, we can observe the development of a verbal system for clinics too. In fact, clinics move from the second position towards the verb, and they are attracted to the verb or attached to a constituent adjacent to it. In Contemporary Modern Persian, the second-position system has disappeared completely, and all the clinics obey the verbal system.