Abstract

The idea that defines quiddity – independence or neutrality in relation to the modalities of existence – allows Avicenna not only to speak of a duality in the being of existing things, but also to use apparently logically incompatible notions to qualify quiddity: that of reality, on the one hand, and that of possibility, on the other. The very conception of the independence of quiddity – which lets us consider quiddity as a separate element in the existing thing – can be recognized in the resolution of the doubt that concludes the Maqāla fī l‑tawḥīd of Yaḥyā ibn ‘Adī. A comparison between Avicenna’s discussion of quiddity in his Metaphysics and the discourse of Yaḥyā ibn ‘Adī confirms the idea that this Christian philosopher and theologian who was active in Baghdad in the tenth century could have played an important formative role in the ontology of the great Persian philosopher.