140 - By All Means Necessary: Avicenna on God

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Avicenna’s proof of the Necessary Existent is ingenious and influential; but does it amount to a proof of God’s existence?



Further Reading

• P. Adamson, “On Knowledge of Particulars,” Proceedings of the Aristotelian Society 105 (2005), 273-294.

• P. Adamson, “From the Necessary Existent to God,” in P. Adamson (ed.), Interpreting Avicenna (Cambridge: 2013).

• A. Bertolacci, “Avicenna and Averroes on the Proof of God’s Existence and the Subject-Matter of Metaphysics,” Medioevo 32 (2007), 61-98.

• M.E. Marmura, “Some Aspects of Avicenna’s Theory of God’s Knowledge of Particulars,” Journal of the Americal Oriental Society 82 (1962) 299-312.

• M.E. Marmura, “Avicenna’s Proof from Contingency for God’s Existence in the Metaphysics of the Shifā’,” Medieval Studies 42 (1980), 337-52.

• T. Mayer, “Avicenna’s Burhān al-Siddiqīn,” Journal of Islamic Studies 12 (2001), 18-39.

• M.S. Zarepour, Necessary Existence and Monotheism: an Avicennian Account of the Islamic Conception of Divine Unity (Cambridge: 2022).


In reply to by Jonathan

Peter Adamson on 6 November 2016

Avicenna's proof

Hi, glad that you liked the episode. I would say no, he doesn't presuppose that the universe is eternal. He does seem to presuppose that something exists (at some point). As long as you have even just one contingent thing, of any duration, preponderated to exist, you can use his proof to derive a Necessary Existent (of course he presupposes a large aggregate of contingents, but it would work if the aggregate only had one thing in it). 

Note that he also doesn't need to assume that all possibilities are realized at some point in time, at least not for these purposes. Your idea that everything will fail to exist at some point, if this could in principle happen, is invoked by Aquinas in his third of the Five Ways, but not by Avicenna.

Nidhal on 23 December 2016



 thanks for this deep and impressive episode.

I would like to get some clarification related to the proof of uniqueness, that is, what prevents the 'NE' from being multiple identical nessecary existents? In your terms, what prevents the 'NE' from being many identical 'Charlies' without any differences at all ?

In reply to by Nidhal

Peter Adamson on 24 December 2016


Good question. Really Avicenna is here just tacitly depending on a principle sometimes called the "identity of indiscernibles": different things must have at least some distinguishing feature, or to put it the other way around, if A has every single property that B has, and vice-versa, then A and B are identical. This is not obvious but it is pretty plausible - in general, when we discover that A and B share all the same features, we tend to think A is B (like, if Clark Kent is never in a different place than Superman, and has all his powers, etc then we can conclude that he is Superman).

In reply to by Nidhal

S.G. on 12 June 2019

Oneness of the Necessary Existent

I think there can be another reply as well: Assume there are two necessary and perfectly identical "Charlies". Then the set of these two, namely {Charlie1, Charlie2}, is also a necessary existent, but different from each of these. So, again, we would have two "Charlies" and a "Buster" (namely the set), and we can apply Avicenna's argument.
On the other hand, an opponent might argue that this set is not necessary, since it is caused by our two "Charlies".

In any case, assuming that Avicenna's argument for a Necessary Existent (or more) is correct (which I do), and that there could in principle be many identical NE's (which I don't, because of Peter's Superman argument), we could still apply my favorite philosophical argument: Ockham's razor. If there is one Charlie, it's useless to assume he has ten thousand identical twins.

Haer on 20 February 2017

Proof of the Truthful on Wikipedia

Hi Professor, I recently added a Wikipedia entry on this proof (titled "Proof of the Truthful", apparently I can't post actual URLs in the comment section). It cites a lot from this chapter and from your other work in "Interpreting Avicenna". Anyway, just want to let you know, but if you're interested feel free to look at it, give feedback or even edit it yourself (it's very easy to do!).

And thanks for doing a podcast on this interesting topic!

Matt on 14 March 2018


Hello professor. First of all, thank you for the podcasts, I have been really enjoying them! 

My question is this. In Avicenna’s proofs for the oneness of the necessary existent he says that two things that are the same, which in this case are the necessary existent, are in fact one thing. (ok, this I understand). But then he says that if a third thing comes along and effects one of the two previously mentioned things, that third thing is the necessary existent, because it caused the difference in the two other things. 

This part is where I am lost. Does this proof of oneness not leave us wondering what caused the two first things mentioned to exist? Where did they come from? I understand that in part they come from the third thing, but for the third thing to be relevant, then it must be interacting with the first two, right? 

Maybe I am completely thinking about this in the wrong way, but I would love it if you could help me understand.

Thanks again,


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