 In the context of the epistemological reshaping of the metaphysics, Avicenna shows first that the subject-matter of this science conforms to all the different characteristics that Aristotle assigns to it in the Metaphysics. Thus, metaphysics is a study of the First Causes and God (cf. Metaph. Α, 1, 981b28–29; Α, 2, 982b9–10), since the First Causes and God are its “goal”. But it is also a study of “the existent” (cf. Metaph. Γ, 1, 1003a20–26), since “the existent qua existent” is its subject-matter. Finally, metaphysics is a study of immaterial and unmoved things (cf. Metaph. Ε, 1, 1026a13–23), since both the First Causes and God, and “the existent qua existent” are realities of this kind. This harmonization of Aristotle’s different points of view is undertaken with the intent of conforming metaphysics to the epistemological canons of the Posterior Analytics, which posit the subject-matter as the fundamental element of every science. Avicenna is the first thinker in the history of philosophy to have devoted a distinct and articulated treatment to the issue of the subject-matter of metaphysics, whose later impact on Arabic and Latin philosophy has been enormous, insofar as it settled the issue of how metaphysics can be both an ontology and a philosophical theology. The other aspects of the scientific reform of metaphysics introduced by Avicenna are also the result of applying the epistemological requirements of the Posterior Analytics to this discipline. In this way, Avicenna bestows on metaphysics an articulated and coherent structure, based on the main elements that the Posterior Analytics spell out as fundamental to every science: the parts, properties, and principles of its subject-matter, and a method that is, as much as possible, demonstrative, in keeping with the Posterior Analytics’ claim that demonstration is the most perfect type of proof.