  This may lead the reader to believe that Khayyam was the first Muslim philosopher to support the theory of the principality of essence, but a more careful reading reveals an interesting twist: namely, that Khayyam’s understanding of how essences came to be casts doubt on his belief in the principality of essence. Towards the end of the Risālah fi'l-wujūd he uses the Neoplatonic scheme of emanation to explain the origin of essences and states: “Therefore, it became clear that all substances  (dhāt)10 and essences (māhiyyah) emanate from the essence of the First Exalted Origin, in an orderly fashion, may glory be upon Him.” The traditional Neoplatonic scheme, at least in Ibn Sīnā’s version, clearly considers this succession to be existential, whereby levels of existence emanate from the One. Khayyam replaces essence with existence here and the question is whether he equates them and thereby deviates from his teacher Ibn Sīnā. Khayyam furthermore explains that “they [essences] are all good in themselves and there is no evil in them in any form or fashion” (Ḍarūrat al-taḍād fi'l-‘ālam wa'l-jabr wa'l-baqā‘, 130). This deviates from the standard definitions of an essence and is much closer to Plato’s forms than the traditional notion of māhiyyah.