It appears that the early Nizari Ismailis showed a particular interest in the doctrine of the Imamate and concentrated their doctrinal investigations. Thus, Hasan bin Sabbah broached the doctrine of talim (authoritative teaching) to the Ismailis. The Sunni observers developed a distinct impression that the Ismailis of Alamut reflected a "new teaching" (al-dawa al-jadida). The new teaching of talimdid not however, entail the formulation of any sect of new doctrines, it was, rather, the reformulation of the fundamental principle of Shia Islam embodied in the doctrine of ilm imparted by Imam Jafar Sadik. Ibn Tughri Birdi (d. 874/1470) writes in his "al-Nujum al- Zahira fi Muluk Misr wa al-Qahira" (Cairo, 1929, 4th vol., p. 77) that, "During the Fatimid Caliphate in Egypt, al-Muizz and later, al- Mustansir had utilized the principle of talim to the fullest extent."
Hasan bin Sabbah, thus did not originate the doctrine of talim, but elaborated and interpreted the doctrine of ilm of Shia Islam abreast of the time. According to "The Cambridge History of Iran" (ed. by J.A. Boyle, Cambridge, 1968, 5th vol., p. 433), "But observers got the impression that there was a "new teaching" associated with the movement which could be contrasted with the old and thus would not be surprising. If there was, however, it was not a wholly new system but a new emphasis and development of a doctrine of long standing among Ismailis and indeed among Shiis generally: the doctrine of talim, authoritative teaching." According to Marshall Hodgson, "It was this doctrine of talim which was especially developed by Hasan-i Sabbah; he turned it into a sharp intellectual tool in keeping with his whole life and demeanor." (op. cit., p. 53)
Hasan bin Sabbah compiled a theological treatise in this context, entitled "Fusul-i Arba'a" (the Four Chapters), which was an Ismaili thesis and in its fully developed form, the doctrine of talim was expounded by him in an Iranian essay. Several writers have mentioned, notably summarized by Shaharistani. In the doctrine of talim, Hasan bin Sabbah consistently emphasized the role of the Imam, with the Prophet having been a link in the logical chain from God to Imam. It became so central to the Ismailis thought that its followers in Khorasan came to be known as the Talimiyya. Many Sunni writers assailed the doctrine of talim in view of their own sense of propriety in opprobrious words. The Abbasids also reacted and hired the famous theologian, Abu Hamid al-Ghazali (d. 505/1111), who tried to refute it in his "Kitab fada'ih al-Batiniyya wa fada'il al-Mustazhiriyya" and other treatises. According to Wilferd Madelung in "Religious Trends in Early Islamic Iran" (New York, 1988, p. 102), "In itself Hasan-i Sabbah's teaching was hardly a radical challenge to Islam. Like Fatimid Ismailism, he insisted on the validity and strict application of the Sharia."