Kasravi is known for his solid and award-winning research on the ancient Azari language and origin of the Azerbaijani people. He showed that the ancient Azari language was an offshoot of Pahlavi language. Due to this discovery, he was granted membership of the London Royal Asiatic Society and American Academy. [احمد کسروی پژوهشگری،سرکشی و خرده نگری by: Khosro Naghed.]
Kasravi proved that the first language of the Azerbaijani people derived from the Persian language and the influx of Turkic words slowly began only much later in Iran's history during the Seljuq invasion. Ahmad Kasravi believed that the true national language of Iranian Azerbaijan was Persian and advocated the use of Persian as the original mother-tongue of Azarbaijanis. In 1927-1928 Ahmad Kasravi led the way in establishing the ancestry of the Safavid dynasty with the publication of three influential articles, and traced the 'official' Safavid family tree contained in the Safvat al-Safa. Kasravi convincingly showed that the ancestors of Shaykh Safi al-Din, who founded the Safavid Order (tariqa), were indigenous inhabitants of Iran and were of pure Aryan (Iranian) stock. Safavid historians have confirmed that the Safavid family hailed from Persian Kurdistan.
Today the consensus among all leading linguists, historians, and anthropologists is that Ahmad Kasravi's findings are the prevailing and accepted academic view that the original language of Azerbaijanis was an old Persian language that later in history took on a Turkish influence.
