This paper traces the process whereby lettrism (‘ilm al-huruf) became widely accepted as a universal science among the intellectuals of 15th century Iran, this largely through the efforts of Sa’in al-Din Turka (1369-1432) and his Isfahan circle. While various elements of lettrism had been vaunted in the Islamicate intellectual tradition from Jabir b. Hayyan (d. ca. 815) and the Ikhwan al-Safa’ (10th c.) onwards, Sa’in al-Din expresses the millenarian universalism endemic to his own day by synthesizing a new brand of intellectual lettrism. Most significantly, he awards this science supreme epistemological status by inverting its relationship to both mystical theory and philosophy: indispensable, all-encompassing matrix, not subsidiary tool. Sa’in al-Din’s subversion of the tradition through lettrism may be seen, for example, in his commentary on the Fusus al-Hikam of Ibn ‘Arabi; uniquely among the host of commentaries on this text, earlier and later, his is thickly veined with lettrist concerns. He also breaks with long and venerable precedent in striving to popularize intellectual lettrism among the Timurid elite, finding a receptive audience in Iskandar Mirza (r. 1409-14) and Baysunghur b. Shahrukh (d. 1433) in particular. This project necessarily involved a new disregard for the secrecy and circumspection so scrupulously observed by previous generations of occultist thinkers, and is thus symptomatic of the larger cultural shift toward a universalist openness that took place in the Islamicate heartlands during the 15th century. The effectiveness of Sa’in al-Din’s retooling of the tradition is reflected in the writings of subsequent Timurid-era thinkers. Two will be touched on here: Jalal al-Din Davani (d. 1503), the prominent illuminationist philosopher and theologian; and Husayn Va‘iz Kashifi (d. 1505), polymath and thoroughgoing occultist. In his concern to preserve the choice fruits of the intellectual tradition, Kashifi, unsurprisingly, penned no less than five lettrist works; his unfinished Javahir al-Tafsir, for example, appears to be the first — and last — lettrist tafsir of the Quran. More surprisingly, Davani treats of both the practical-magical and theoretical aspects of lettrism in two separate works, Tuhfa-yi Ruhani fi Khavass al-Huruf and R. Tahliliyya. While it is Kashifi’s catchall approach that serves to canonize the new importance of lettrism in intellectual circles, Davani’s unexpectedly high regard for the science — even he elevates it above both philosophy and mystical theory, that is to say, his own fields of expertise — stands eloquent testimony to the ubiquity of occult philosophy in 15th century Iran.