By the 4th century BCE, the late Achaemenid period, the inscriptions of Artaxerxes II and Artaxerxes III differ enough from the language of Darius' inscriptions to be called a "pre-Middle Persian," or "post-Old Persian." Old Persian subsequently evolved into Middle Persian, which is in turn the ancestor of New Persian. Professor Gilbert Lazard, a famous Iranologist and the author of the book Persian Grammar states:

Persian , also known by its endonym Farsi (فارسی, Fārsī, [fɒːɾˈsiː] (listen)), is a Western Iranian language belonging to the Iranian branch of the Indo-Iranian subdivision of the Indo-European languages. Persian is a pluricentric language predominantly spoken and used officially within Iran, Afghanistan and Tajikistan in three mutually intelligible standard varieties, namely Iranian Persian (officially known as Persian), Dari Persian (officially known as Dari since 1964) and Tajiki Persian(officially …