 The Necessarily Existent is therefore absolutely one, indivisible and unique (Ilāhiyyāt, I, 7, 47, 6–9; cf. VIII, 4, 5) and the properties of the possible are deducible as opposite to these (e contrario) (Ilāhiyyāt, I, 7, 47, 10–19): the possible is caused and twofold (Ilāhiyyāt, I, 7, 47, 18–19); in itself it does not exist and therefore always receives existence from something else. The hypothesis of a possible existent thing, which can both exist and not exist, leads necessarily to positing a cause that makes it necessary (by virtue of another). If the possible were not rendered necessary by its cause, but—given the cause and its relationship to it—were still possible, it would be continuously in a state in which it could exist and not exist. But since it exists (the analysis concerns existing things), its relation to the cause must be necessary. Analogously, if the cause were in its turn possible, it would refer to a further cause that would explain the existence of both the caused thing and its cause. If even this further cause were possible, it would perforce have recourse to a third one, and so on. One could not proceed ad infinitum (as an Aristotelian, Avicenna accepts only a potentially infinite series of causes) and could consequently not explain the actual existence of a thing: the thing would still be possible and therefore non-existent.