The Divine Substance as Aristotle’s Substantia Prima: Yaḥyā b. ʿAdī and his Trinitarian Doctrine

The famous Miaphysite and Arab Christian philosopher and theologian Yaḥyā Ibn 'Adī (d. 974) wrote various apologetical works in defence of the Trinitarian dogma against Muslim understanding of the Christian Trinity as Tritheism. In dealing with this challenge, however, Yaḥyā Ibn 'Adī, offers a new approach to the Trinitarian doctrine where the focus is on the oneness of the subject and the multitude of its definitions. In this contribution I aim to present the Trinitarian doctrine of Yaḥyā in his work against Abū 'Īsā al-Warrāq (d. 994) ‒ as well as in his other Trinitarian writings ‒, highlighting the importance of his use of the 'analogy of Zayd' and the 'analogy of intellect', as a key to understanding his metaphysical system. In addition, this study aims to argue the possible relationship between Yaḥyā’s doctrine and his Miaphysite predecessors, who in the sixth century had to face the so-called 'Tritheism' of John Philoponus (d. 570) and his followers.