Persian was not the only language transformed by the demographic upheaval consequent to the formation of the Persian Empire. Other languages of the Iranic family, particularly Parthian and Bactrian, were reduced in ways quite similar to Middle Persian. Although we lack texts in those two languages contemporary with the Achaemenian Empire, this chapter argues that their uncanny similarity with Middle Persian in grammatical restructuring was due to similar demographic conditions and probably also by convergence through multilingualism. Counterexamples of Iranic languages later documented on the fringes of or outside of the former Persian Empire show that they were not affected by the same changes. The conditions prevailing in the Persian Empire were likely responsible for the similarity in type shared by Middle Persian, Parthian, and Bactrian.

This book is about the early evolution of the Persian language, specifically the emergence of Middle Persian from Old Persian in the time of the Achaemenian Persian Empire. The Introduction explains the project and defines critical terms. The concept of linguistic history is explained, followed by further notes on the critical use of certain terms and a sketch of the plan of the book.