The Proof of God’s Existence and the Science of Metaphysics

Peter Adamson has emphasized the special place the proof of God’s existence has in Ibn Sīnā’s philosophical thought: “[i]f one were asked to name Avicenna’s greatest contribution to the history of philosophy, one might reasonably choose his proof of God’s existence” (Peter Adamson, “From the necessary existent to God,” in Interpreting Avicenna: Critical Essays, ed. Peter Adamson, 170–189). He is concerned with establishing what kind of existence out of the three kinds of existence that characterize the entirety of beings describes God. The natural science has a subject-matter […] and that subject-matter is the body insofar as it is moving and resting […]. As for the enquiry about whether the body is made up of atoms, whether it is finite or not, whether every body has extension and form or not, this relates to the science that is after nature (ʿilm mā baʿdal-ṭabīʿa) [i.e., metaphysics] for these are states of the body insofar as it is an existent, not insofar as it is subject to change, and this is the enquiry about the kind of its existence which is characteristic of it (baḥth ʿan naḥwwujūdihi alladhī yakhaṣṣuhu), that is, [the question of] which existence is characteristic of it (ayy wujūd yakhaṣṣuhu) [my emphasis] (Abū ʿAlī Ibn Sīnā, al-Taʿlīqāt, ed. ʿAbdal-Raḥmān Badawī (al-Qāhira: al-Hayʾa al-Miṣriyya al-ʿĀmma li’l-Kitāb, 1973), 171–172). The discussion of whether the body is made up of atoms is the discussion of the kind of its existence (naḥwwujūdihi), and so is the discussion of whether it is made up of matter and form. This is not related to physics. […] Movement belongs to the accidents of the subject matter of physics, which is the body insofar as it is moving or resting, therefore to establish these accidents has to take place in physics. But these do not belong to the parts of the body insofar as it is made up of form and matter, therefore establishing them belongs to metaphysics (Ibn Sīnā, al-Taʿlīqāt, 172).

1. The Twofold Division of Existence—Proving God’s Existence?
2. Ibn Sīnā writes: every existent—when you consider it in terms of its essence (dhāt), not considering anything else than that—existence is either necessary for it or not. If it is necessary, it is the truth by virtue of its essence (al-ḥaqq bi-dhātihi), the necessarily existent by virtue of its essence (al-wājib al-wujūd min dhātihi), it is the self-subsisting (al-qayyūm). If it [i.e., its existence] is not necessary, it may not be said that it is impossible by virtue of its essence (mumtaniʿ bi-dhātihi), since it has been posed as existent. Rather, if a condition is coupled with it, when its essence is considered, such as the condition that its cause does not exist, it becomes impossible, or such as the condition that its cause exists, it becomes necessary. If no condition is coupled with it, neither the existence of a cause nor its non-existence, only a third option remains when considering its essence: possibility (al-imkān). It is, thus, when considering its essence, the thing which is not necessary nor impossible. Every existent is, then, either necessarily existent by virtue of its essence or possibly existent by virtue of its essence (mumkin al-wujūd bi-dhātihi). In the subsequent discussion, Ibn Sīnā adds that “the existence of everything that is possible is due to another” (Ibn Sīnā, al-Ilāhiyyāt min al-Ishārāt, 20), even in the case of an infinite chain of causes and effects which are all possible in themselves and which has to terminate in an ultimate cause which is not itself an effect (Ibn Sīnā, al-Ilāhiyyāt min al-Ishārāt, 21 and 26). A similar version of this twofold division of existence also appears in Ibn Sīnā’s al-Najāt. There he writes: the necessarily existent (al-wājib al-wujūd) is the existence which when assumed to be non-existent—an absurdity arises.

The possibly existent (al-mumkin al-wujūd) is […] that which is not necessary in any respect (lā ḍarūra fīhi), that is, in terms of its existence and its non-existence. […] Every possibly existent by virtue of its essence, if its existence manifests itself (ḥaṣala), it is necessarily existent due to another (bi-ghayrihi). Ibn Sīnā writes: there is no doubt that there is existence. Every existence is either necessary or possible. If it is necessary, the existence of the necessary is assured (ṣaḥḥa). This is what is sought. If it is possible, we shall show that the possible ends, in terms of its existence, in a necessarily existent. […] We pose that every cause in an aggregate [of causes and effects] (jumla) is possibly existent, so the [ultimate] cause is then external to the aggregate and it is necessarily existent by virtue of its essence. This means that the possible things end in a cause which is necessarily existent, and it is not the case that every possible thing has a cause that is [also] possible ad infinitum.