The Hindi–Urdu controversy arose in 19th century colonial India out of the debate over whether the Hindi or Urdu languages should be chosen as a national language. Hindi and Urdu are mutually intelligible as spoken languages, to the extent that they are sometimes considered to be dialects or registers of a single spoken language referred to as Hindi-Urdu or sometimes Hindustani. But they are written in very different scripts: Devanagari (for Hindi) and a modified Perso-Arabic script (for Urdu), each of which is completely illegible to readers literate only in the other.