 The so-called distinction between essence and existence reveals an unavoidable modal characterization of being. The starting-point of Avicenna’s metaphysics is the existent, but the analysis Avicenna applies to it (see Ilāhiyyāt, I, 6) does not concern what exists insofar as it is existent (the existent is indefinable: Ilāhiyyāt, I, 2, 13, 8–13), but instead concerns the modality that explains the relation that what exists has to its own existence: an existent can be either necessary in itself (ḍarūrī; wāǧib: it is then also necessarily one) or possible (mumkin) in itself (this is the case of every existent with the exception of the First Principle: Ilāhiyyāt, I, 6, 37, 7–10). These distinctions thus reveal the inner complex of relations that explain existence: not only are the notions of existent and thing primary, but so are those of unity, necessity and—to some extent—possibility (Ilāhiyyāt, I, 5, 29, 5–6; 30, 3–4; 35, 3–4; 36, 4–5). If, on the one hand, the primacy of these notions ultimately leads to positing the transcendentals (de Libera 1994; Aertsen 2008; Bertolacci 2008a; Koutzarova 2009), on the other hand they reveal that, in the world, being is always the being of something, so that the notions of existence (unity and necessity), although separate from that of the thing, can never be isolated from the thing or from the relation that it has to existence itself. A crucial point is that the division between necessity and possibility regards something that exists. Avicenna speaks, in fact, precisely of what is “necessarily existent” or of what is “necessary as far as existence is concerned” (al-wāǧib al-wuǧūd), and of what is “possibly existent” or “possible as far as existence is concerned” (al-mumkin al-wuǧūd). What is considered is the quiddity (māhiyya) or essence (ḏāt) of what exists: the modality of existence depends, in fact, not on existence (which would be impossible), but on essence (although in the case of the Principle there is no essence different from its own existence; see  Section 2.4).