Avicenna et Aquinas: De Esse et Essentia Dei (summarium dissertationis philosophiæ)

This thesis undertakes a comparative analysis of the philosophical contributions of Avicenna and Aquinas, focusing on the influence of Avicenna's Sufficientia on Aquinas' De Ente et Essentia, Summa Contra Gentiles, and Summa Theologiae. The central theme of this study is the transmission and adaptation of Avicenna's metaphysics, especially the distinction between essentia (مَاهِيَّة) and esse (وجود) within Aquinas' Sacra Doctrina. This Avicennian distinction, first integrated into De Ente et Essentia, became the basis for Aquinas' demonstration and proof of God's existence in his Summa Contra Gentiles I. and Summa Theologiae I. This thesis also investigates the bearing of Aristotle's Metaphysica on both Avicenna and Aquinas. It distinguishes between Aristotelian and Avicennian influences on Aquinas' metaphysical theology of Sacra Doctrina concerning the subject matter of metaphysics, the definition of God (or lack thereof), the essence and existence of God, the demonstration of God's existence, the proofs of God's existence, the unity and oneness of God, and divine thought and intellect. This thesis employed a rigorous methodology that combined historical textual analysis, philosophical exegesis, and comparative conceptual analysis, examined primary texts in Koine Greek, Arabic, and Latin, alongside authoritative English translations, and traced the transmission of Aristotle's and Avicenna's metaphysics in Aquinas' texts. Additionally, the study engaged extensively with both ancient and contemporary scholarly writings on Aristotle, Avicenna, and Aquinas, contextualized and interpreted their metaphysical arguments, and showed that Avicenna's metaphysics was integral to Aquinas' knowledge of the nature of God as the necesse esse (واجِبُ الوُجُود) and ipsum esse subsistens (أن يكون قائما بنفسه) whose essence is identical to His existence. These concepts informed Aquinas' doctrines on God's divine simplicity and unity and impacted the fundamental doctrines of the Roman Catholic Church's dogmatic and natural theology. This thesis contributed to comparative medieval philosophy by demonstrating the profound philosophical influence of Avicenna's Islamic philosophy on Thomism. The engagement between these two great philosophers reflects the universality of metaphysical inquiry and demonstrates its enduring relevance to Shia Islam and Western Christianity. Avicenna and Aquinas left an indelible mark on the development of medieval scholastic philosophy, proving that Peripatetic metaphysics transcends temporal, geographic, linguistic, cultural, and religious boundaries in the interest of the ultimate Truth.