There is a strange persistence in many Western studies of the religious history of Islamic Iran to be concerned almost solely with small sects and extremist religious movements. A notable feature of the Islamization of Iran that is reflected in the work of the Persian scholars, who were concerned with the religious sciences is strong opposition to the Zanādiqa and similar heterodox groups. The sciences dealing with the Quran are divided traditionally into those dealing with the recitation of the Book and those dealing with commentary upon it and the meaning of its content. The Quran itself provides in many places intellectual evidence and demonstration for its arguments and is the example for all later developments of Islamic religious sciences in which rational arguments are provided for articles and principles of faith. The efforts of Persian scholars in helping to lay the foundation of many of the Islamic sciences during the early period continued into the Saljuq and Timurid periods.