 The causal chain is the key idea of the argument by means of which Avicenna, in Ilāhiyyāt VIII, 1–3, posits a First Cause, in accordance with—at least partly—a cosmological scheme. Indeed, according to some scholars, this is the only place to track down a demonstration of the existence of the Principle in the Metaphysics of the Book of the Healing (Bertolacci 2007; De Haan 2016). As an Aristotelian, Avicenna establishes formal, material, efficient and final causes. Consequently, in order to demonstrate the existence of a First absolute Principle, he must show not only that “for every causal order there is a first principle” (Ilāhiyyāt, VIII, 1, 327, 9) but also that causal chains are all based on the same First Principle. The demonstration of the finiteness of the agent causes, from which every other series derives is an exemplar and serves as a general proof. Avicenna deduces the finiteness of all series (Ilāhiyyāt, VIII, 1, 329, 5–9) from the finiteness of an unqualified causal series: thus all series refer to a First Principle that is both an agent (ʿilla fāʿiliyya) and a final or completive (ʿilla tamāmiyya) cause (Ilāhiyyāt VIII, 1–3; Wisnovsky 2003a).