 On this basis, Avicenna deduces the properties of what is in itself necessarily existent. The first is being uncaused. It is in fact “evident” (ẓāhir: Ilāhiyyāt, I, 6, 38, 1) that the necessary has no cause: to have a cause means to exist by virtue of something else, and what exists by virtue of itself cannot exist by virtue of another, nor can it exist by virtue of itself and at the same time not exist by virtue of itself. The second property is uniqueness: the necessary has no “homologue”: there is nothing that—even if equivalent to it as regards its definition—could exist together with it and thus occupy the same rank of existence, without being either its cause or its effect. Two necessary beings would in fact either both be caused (and therefore both non-necessary), or refer to a cause that would make only one of them exist; but in the latter case, they could no longer be defined as equivalent or homologous (mutakāfī al-wuǧūd): one would be possible and caused, while the other—in the absence of another external cause—would be its cause (Ilāhiyyāt, I, 6, 39, 17–42, 7). Indeed, as shown by the discussion of the relations between form and matter (Ilāhiyyāt II, 4), and also soul and body (see the psychological part of the Book of the Healing, the Kitāb al-nafs; Avicenna’s De anima, V, 4), the co-existence of two things always implies the action of a cause that makes them exist (Lizzini 2004).