Avicennas Proof from Possibility

The proof of the existence of the Necessary of Existence through Itself appears in Chapter 4 of the Physics and Metaphysics of the Ishdrdt (11.4.9-15). Following a discussion of causation, Avicenna introduces the concepts possible existent and necessary existent , and submits that every existent must be either possible of existence in itself, or necessary of existence in itself Ishdrdt 11.4.9). A thing that is possible in itself is predisposed as such to neither existence nor nonexistence. So if such a thing becomes existent, there must be something other than itself that tips the balance and renders its existence preponderant to its nonexistence. Therefore, the existence of a possible thing must be caused by another Ishdrdt 11.4.10). What Avicenna intends by cause here is a metaphysical efficient cause (that is, a cause of existence), as opposed to a physical efficient cause (that is, a cause of motion). As such, the cause of a possible existent must coexist with its effect  

1 Avicenna, Ishdrdt, 3, 19 27. For a discussion of the proof as it appears in the Najdt, see McGinnis, Avicenna, 163-168. 

5 This reading finds explicit confirmation in the Ncydt (567 cf. Davidson, Proofsfor Eternity, 299 ff.). In his commentary on the proof as it appears in the Ishdrdt, al-EazI rightly points out that it lacks a vital ingredient—namely, an indication of whether the series of successive causes possible of existence are ordered temporally, or are simultaneous. He writes that 

it is obvious that possible existents do actually exist. Each possible existent must be caused either by another possible existent, or by an existent necessary through itself. As the existence of the latter has yet to be demonstrated, the argument proceeds on the assmnption that the cause is a possible existent. If this second possible existent is caused by yet another possible existent, which is caused by yet another possible existent, then the series of successive causes possible of existence may be either infinite or finite. The next passage Ishdrdt 11.4.11), therefore, begins with the disjimctive either (immd), although Avicenna here only considers the former disjimct, namely that the series is infinite (which is why, in what follows, 1 have replaced either with if ). He writes  

If [the series of causes possible of existence] regresses ad infinitum, then each imit in this series will be possible in itself The whole (Jumla) is dependent on these [emits]. Therefore, it too is not necessary, but must be necessitated by another.  

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Discussed in Chapter 5. In Ishdrdt II.4.9-15, Avicenna proves the existence of the Necessary of Existence through Itself starting from the existence of possible existents. An outline of the argument is provided below, and shall not be reproduced here. Suffice it to say that in the course of the proof, Avicenna opines that if we suppose an infinite series of possible existents, each being an efficient cause that brings the next item in the series into being, the series taken as a whole (Jumla) will be possible of existence, and hence caused by an efficient cause external to the series. 

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