 The background of this distinction is Aristotelian. In a very broad sense its origin can be discovered in Aristotle’s Posterior Analytics (II Β 92b10)—where the question that asks “if a thing exists” is separate from the one that asks “what a thing is”—in the Metaphysics (Δ V.5, 1015a20–b15; 7, 1017a7–b10; but also Ε and Z)—where the various meanings of “being” are differentiated and the question of essence (ousia, to ti en einai) is posed—and in De interpretatione 11 21a25–8; Lizzini 2003; Menn 2013). Moreover, although original in its development Avicenna’s distinction uses terms and concepts that can be found in both the philosophical and the theological traditions of classical Islam: in al-Fārābī’s Book of Letters (K. al-Ḥurūf; cf. Menn 2008), in Yaḥyā ibn ʿAdī’s discussion of natures (Rashed 2004; Benevich 2018 and 2019; Janos 2020) and also in the distinctions of Muʿtazilite Kalām, in which a “thing” was conceived of as separate from existence (Jolivet 1984; Wisnovsky 2003a).