  Although the distinction between the principality of wujūd (aṣālat al-wujūd) and the principality of māhiyyah (aṣālat al-māhiyyah) can be found among early Muslim philosophers, the subject matter became particularly significant in later Islamic philosophy, especially through the School of Iṣfahān and the work of its most outstanding figure, Mullā Ṣadrā. This is important for our discussion since Umar Khayyam may simply have presented the arguments for and against the priority and posterity of essence and existence without attaching much significance to their philosophical consequences, as was the case in later Islamic philosophy.