Dari is the variety of the Persian language spoken in Afghanistan. Dari is the term officially recognized and promoted since 1964 by the Afghan government for the Persian language. Hence, it is also known as Afghan Persian in many Western sources. As defined in the Constitution of Afghanistan, it is one of the two official languages of Afghanistan; the other is Pashto. Dari is the most widely spoken language in Afghanistan, according the World Factbook spoken by 50% of the Afghan population, and it is the native language of approximately 25–33% of the population, serving as the country's lingua franca. The Iranian and Afghan types of Persian are mutually intelligible, with differences found primarily in the vocabulary and phonology. Originally, Dari was the name given to the Old Persian language at a very early date and widely attested in Arabic and Persian texts since the 10th century. In historical usage, Dari refers to the Middle Persian court language of the Sassanids.