Changing of Old Iranian Preverbs

old Iranian speakers limited the meaning of verbs through combining preverbs with them and herewith could make Particle Complex Verbs out of them. In the first phase of long term history of preverbs, different mechanisms were working in the case of grammaticalization to generate them from Proto-Indo-European particle adverbs. Next in the second phase, some other mechanisms made morphological, semantic and phonological changes. They changed preverbs to verbal prefixes and then to dead prefixes. Finally, Iranian languages made new preverbs through changing old adverbs and prepositions and started to use them instead of the old ones. These newly invented preverbs were used vastly in the middle Iranian languages and continued to be used with a few changes even in New Persian. The purpose of this paper is to investigate mechanisms involving the changes of old preverbs from Proto-Indo-European to old Iranian and then to middle Iranian languages.