In Necessary Existence and the Doctrine of Being in Avicenna’s Metaphysics of the Healing Daniel De Haan explicates the central argument of Avicenna’s metaphysical masterpiece. De Haan argues that the most fundamental primary notion in Avicenna’s metaphysics is neither being nor thing but is the necessary (wājib), which Avicenna employs to demonstrate the existence and true-nature of the divine necessary existence in itself. This conclusion is established through a systematic investigation of how Avicenna’s theory of a demonstrative science is employed in the organization of his...