Avicenna (d. 1037) famously held that God’s essence is existence itself. This rather opaque conception of God yielded a set of interpretations among his commentators that both proved decisive for the fields of philosophy and rational theology and opened the door to a striking challenge to God’s unity, one that could not be resolved under available frameworks. New, finer ontological distinctions in post-Avicennian metaphysics, like the distinction between God’s specific existence (wujūd khāṣṣ) and the general, equivocal concept of existence (wujūd ʿāmm) that it instantiates, or the distinction between the quintessence (kunh) of a thing and its aspect (wajh), paved the way for arguments in favor of the possibility of a second God. In this paper, I show how the problem of God’s unity elicited a bold reinterpretation of Avicenna on the part of Jalāl ad-Dīn Dawānī (d. 1501/2), perhaps the most important scholar of the rational sciences in the lead up to the turn of the Islamic millennium. By his lights, Avicenna meant that God is existence itself, such that only he really exists and all other things can only be said to exist metaphorically and insofar as they stand in some connection to him. This idea has antecedents in the works of Ibn ʿArabī (d. 1240) and his commentators, but I will sketch out how Dawānī motivates it within the discourse of the rational sciences. Honing in on Dawānī’s commentary on Suhrawardī’s (d. 1191) "Temples of Light" and his "New Treatise on the Establishment of the Necessary Existent," I show how he unfolds a new set of concepts out of his rereading of Avicenna in order to disarm arguments for the possibility of a second God, concepts which would frame rational inquiry into God and his attributes from the Ottoman to the Mughal world in the following centuries. By way of conclusion, I point to how Dawānī’s conception of God as existence itself raises a new set of worries concerning the relation between technical and ordinary language. Whether we take him to be a philosopher or a rational theologian, Dawānī stumbles on the age-old problem of how metaphysics might justify its departures from ordinary speech—why we should be convinced that when we say something other than God exists we really only mean existence metaphorically.