<![CDATA[This article re-examines the relationship between the metaphysical systems of Avicenna (Ibn Sīnā) and Thomas Aquinas by questioning the widespread assumption of ontological continuity grounded in their shared distinction between essence and existence. While Avicenna’s māhiyyah–wujūd distinction is often treated as the conceptual foundation later appropriated by Aquinas, this study argues that such a reading obscures a decisive ontological divergence rather than illuminating a genuine metaphysical lineage. Employing the realist metaphysical framework developed by the Lublin School, particularly its emphasis on esse as the act that constitutes being as such, the article undertakes a conceptual and historical analysis of both systems to uncover their underlying ontological architectures. In Avicenna’s metaphysics, existence is understood as a determination received by essence through causal dependence on the Necessary Being, yielding an emanative model of reality structured by hierarchical necessity. By contrast, Aquinas situates existence as actus essendi, the fundamental act through which beings participate in actuality itself, thereby grounding a participatory account of the God–creature relation. The article demonstrates that this difference is not merely semantic or theological but reflects two incompatible ontological models, emanation and participation, that entail divergent accounts of causality, contingency, and divine transcendence. By foregrounding this metaphysical fault line, the study contributes to comparative philosophy by moving beyond narratives of influence or terminological borrowing. It also shows how the Lublin School’s realist criteria provide a rigorous methodological tool for evaluating metaphysical systems across traditions. Ultimately, the article argues that an explicitly ontological approach is indispensable for clarifying both inter-traditional dialogue between Islamic philosophy and Thomism and contemporary debates concerning the nature of existence itself.]]>
