This paper is an attempt to explore the prepositions used to encode the agent in Persian passive constructions. According to Givón (1983) the main function of the passive constructions is to defocus the agent. As the general trend in Persian is to omit this defocused agent, we will stylistically divide the passive constructions into two main sub branches, namely unmarked and marked passives according to whether or not the agent is included. Having analyzed the prepositions using in the passive construction (e.g. t { v { ssot-e, be d { st-e, b A , { z suy-e, { z t { r { f-e, and be v { sile-y-e) a complete semantic characterization of the type of agent that normally occurs with these prepositions will be provided. The results indicate that, in contrast to some linguists who treated the prepositions in the passive construction as stylistic forms, they are not always interchangeable; in fact they are meaningful which have a prototype for the type of agent that co-occurs with them.
