Grammaticalization of heštan in Persian literary texts

In the Persian literary texts, the verb hesht and its present stem hel- have been used with mood's lexical meanings and grammatical function. On the other hand, the past stem of the verb is used in the form helid that is analogical formation. In this article, the root of the verb in the old period of Iranian languages; its main meaning, and other lexical meanings in three periods of Persian language has been examined and the process of semantic evolution and its change to grammatical form for representing modal concept has been described. Hištan is derived from root harz in Avestan Language to meaning “to abandon”, “to leave” and in Middle Persian and Persian literary texts besides "abandoning" mean, is used to mean "putting", "assigning", and "appointing" and also. Moreover, it has become a tool to express the permission modality in Middle Persian. In the Persian literary texts, gozāshtan has also represented the modal concept of permission. Gradually, the use of gozāshtan for denoting this concept has become dominant, and heštan has become eliminated.