A work, entitled Minhāǧ al-farāʾiḍ, is of questionable attribution, even if a copy of the ms clearly mentions al-qāḍī l-Nuʿmān as its author. This paper wants to re-affirm the paternity of al-Nuʿmān and the originality of the Ismaili jurisprudence. This short treatise is examined with reference to the legal writings of al-Nuʿmān. The comparative analysis of legal doctrines, both between the different works of al-Nuʿmān and between the Ismaili fiqh and the legal works of the different schools, leads to outline the development of the Ismaili law and the interrelations between jurists of different schools. It results that Minhāǧ al-farāʾiḍ represents the most ancient stage in the formation of the Ismaili jurisprudence.