Avicenna’s ‘Proof’ for the Existence of God

Author: Farbod Akhlaghi
Categories: Philosophy of Religion, Islamic Philosophy, Metaphysics, Historical Philosophy, Global Philosophy
Word Count: 999

If someone told you that they could prove that God exists simply because something—anything!—exists, would you believe them?

Probably not. But the Persian and Muslim philosopher, physician, and polymath Avicenna (980–1037) would.^[1] He argued that God’s existence can be established from the mere fact that anything exists at all.^[2]

This essay presents and explains what’s called Avicenna’s ‘proof’ for the existence of God.^[3] It is likely the most influential argument in the history of philosophy in the Islamic world.^[4]

1. Necessary and Contingent Existence

The argument relies upon a distinction between how something—an existent—can exist necessarily or contingently.^[5]

Sadly, it seems the world could have existed without you or me in it. So, we exist contingently. The same also seems true of tables, cats, this essay, and the rest of the physical universe. These things can and do exist, but they need not have.

Contingent things, Avicenna thinks, have essences or natures that do not guarantee their existence.^[6] This is true of you and me: after all, lots of possible humans do not exist!^[7] Contingent things require something to cause and sustain their existence.^[8]

A ‘necessary existent’ would have an essence that guarantees its existence. If so, then that entity’s existence is uncaused, and its continued existence depends upon nothing.^[9] Avicenna calls such a thing ‘necessary-in-itself.’^[10]

2. Why Proving the Existence of a Necessary Existent Allegedly Proves God Exists

Abrahamic faiths take God to have several divine attributes, including uniqueness, simplicity, perfection, and necessity.^[11]

For Avicenna, one divine attribute is special: necessity. He argues that God’s being a necessary existent is what entails that God is unique (there is only one God), simple (lacks proper parts^[12]), and more.^[13]

So, to establish God’s existence, Avicenna wants to show that something exists that is necessary-in-itself with his ‘proof.’ Then, he wants to show that all the other divine attributes follow from that entity existing necessarily.^[14]

3. The ‘Proof’

At its most simplified, the ‘proof’ is this:  

(1) Something exists;

(2) If something exists, then there is a necessary existent;

(3) So, there is a necessary existent.^[15]

Avicenna expands upon this argument in multiple ways.^[16] The version most often called his ‘proof’ is the following:

Suppose something exists. If it exists necessarily, then there is a necessary existent.^[17] If it exists contingently, then Avicenna considers the collection of everything that exists contingently—everything that exists but may not have—like you, me, and the rest of the universe. Call that collection ‘X.’^[18]

Next, Avicenna argues that either X exists necessarily—so there is a necessary existent^[19]—or contingently.

The latter would mean X’s existence has a cause. That cause will be a necessary or contingent thing.

If necessary, there is a necessary existent.

If contingent, then that cause must be a part of the collection of everything that exists but may not have, namely X. But this means X would be causing itself to exist!^[20] That is impossible.

So, if anything exists, it follows that something necessarily exists. Thus, something necessarily exists! 

More precisely:

(P1) Something exists. (1)

(P2) If something exists, then either that thing exists necessarily or contingently.

(P3) If that thing exists necessarily, then there is a necessary existent.

(P4) If that thing exists contingently, then the totality or collection of everything that exists contingently—X—exists.

(P5) If X exists, then it exists necessarily or contingently.  

(P6) If X exists necessarily, then there is a necessary existent.

(P7) If X exists contingently, then what causes X to exist is either necessary or contingent.

(P8) If the cause of X’s existence is necessary, then there is a necessary existent.

(P9) If the cause of X’s existence is contingent, then X must cause its own existence.

(P10) Nothing can cause itself to exist.

(C1) So, if X exists contingently, what causes X to exist is a necessary existent.

(C2) So, if something exists, then there is a necessary existent ((2)).

(C3) So, there is a necessary existent ((3)).^[21]

Whether Avicenna thought reason alone justifies (1) and (2)––or if experience was needed––is controversial.^[22] This complicates comparisons with other arguments for God’s existence. Still, Avicenna’s argument comes centuries before similar ‘contingency arguments for God’s existence’ from Aquinas (1225-1274) and Leibniz (1646-1716); avoids appealing to infinite regresses, unlike many ‘cosmological arguments’; and, unlike many ‘ontological arguments’, God’s perfection plays no role.^[23]

4. Three Objections

In general, a property enjoyed by every part of a whole is not always enjoyed by the whole itself. Think of a large building made of many small bricks: each brick is small, but the whole building is not! Thinking that what’s true of the parts must also be true of the whole is the fallacy of composition.

(P5) suggests that X itself is either necessary or contingent. But even if parts of X—e.g., you or me —can be necessary or contingent, why think the collection of all contingent things itself can? We should be careful here: if every brick was red, it would not be a mistake to say the whole building was red!^[24]

(P7) assumes that if something exists contingently, then something caused it to exist.^[25] Why couldn’t the universe exist contingently without a cause, and yet not be necessary? Avicenna thinks this is incoherent. Contingently existing things must be caused to exist because what they are (their essences) does not guarantee their existence. An alternative account of contingency is required to make this objection coherent.^[26]

Avicenna’s proof also suggests that God necessarily created the world. As God necessarily exists, God is always causing and sustaining the world: everything that, without God, would not exist. Creation thus becomes not a ‘freely willed, gratuitous, [or] generous’ divine act, but something God had to do.^[27] A Muslim might think this false, perhaps even heresy.^[28]

5. Conclusion

If Avicenna is right, God’s existence follows from a seemingly undeniable premise: something exists. His ‘proof’ promises to take us from the undeniable to one of the most controversial claims imaginable. If successful, this would be, mildly put, one of the greatest discoveries ever made.

Notes

[1] ‘Avicenna’ is a latinization of ‘Ibn Sīnā,’ from the full name ‘Abū ‘Alī al-Ḥusayn ibn Abdallāh Ibn Sīnā.’ He was arguably the most important philosopher in the history of the Islamic and Persianate world, and he was a physician of monumental significance to the history of medicine. He also left us a fascinating autobiography (Avicenna 1974 [ca. 1037]). See Adamson (2023) and Gutas (2025) for an overview of Avicenna’s life and work.

[2] Avicenna thought God’s existence was neither self-evident nor something you should believe without proof: ‘how can an existence which one despairs of demonstrating be legitimately admitted?’ (Avicenna 2005 [ca. 1020s]: Ch.1.1., §1.1.). Proving God’s existence, he insisted, was a job for metaphysics.

[3] Avicenna’s name for his ‘proof’ is ‘burhān al-siddīqīn.’ This is translated as ‘proof of the sincere’  (Legenhausen 2005), ‘the Demonstration of the Faithful’ (Adamson 2016: 126) and ‘the Proof of the Veracious’ (Rizvi 2019: §3.3.). Avicenna, in the last section of the fourth Class of his Remarks and Admonitions (see Zarepour 2022: 8 for translation of the relevant passage), sees two ways of proving God’s existence: arguing by appeal to God’s actions, or by reflection on existence itself. The latter, he claims, is the most secure and noble way to prove God’s existence, reflecting on existence itself and not indirectly through God’s creation and action. He calls this the way of the ‘sincere’ or ‘veracious,’ or those most ‘faithful.’ This raises the question of whether Avicenna’s argument is an ‘ontological’ or ‘cosmological’ argument. I return to this in §3.

[4] After Avicenna, it is very common for God to be described by Muslim philosophers and theologians by Avicenna’s term ‘necessary existent’ (wağib al-wuğud) found in his ‘proof.’ See Davidson (1987, Chs. IX and X), Legenhausen (2005), and Morvarid (2008; 2021) for the reception of the argument by philosophers, theologians, and others after Avicenna. 

[5] For an introduction to these what are called ‘modal’ concepts or categories, see Possibility and Necessity: An Introduction to Modality by Andre Leo Rusavuk.

[6] Avicenna (2005 [ca. 1020s]: Ch. 1.5., §§9–10). Often translated as ‘essence,’ Avicenna uses māhīya, dāt, ḥaqīqa, and on occasion tabī’a throughout his work. See Bertolacci (2012), Marmura (1980), and Morewedge (1972) for discussion of Avicenna’s distinction between the essence of something and whether that thing exists. Some find precursors of this distinction in Aristotle (e.g., in Posterior Analytics 2.1, 89b23–25), in Plotinus (Gerson 1994; Corrigan 1996), and in earlier Islamic philosophy (e.g., Adamson 2002 in al-Kindi) and theology or kalām (Winovsky 2003: Chs. 7–9). Avicenna undoubtedly introduced novel terminology to draw this distinction in its until-then most explicit form and wielded it pervasively in his metaphysics. See Adamson & Benevich (2023) for translations of some relevant passages from Avicenna, of many in the Islamic world who reacted to Avicenna’s essence-existence distinction, and for more general discussion of the existence-essence distinction in Islamic philosophy (also see Benevich 2025).

[7] Think of any fictional human character you like. It is part of the nature of that character to be human; without being human, they would be a different character. But their being human doesn’t seem to be enough for them to exist!

[8] By ‘cause’, Avicenna means something stronger than what we typically mean by physical causation: ‘X causes Y if and only if Y’s existence is bestowed by and dependent on X’s existence’ (Zarepour 2022: 16). So while your parents physically caused you to exist, they are not the cause of your existence in Avicenna’s sense because your continued existence doesn’t depend upon them. See Richardson (2013) for Avicenna’s notion of an ‘efficient cause.’ 

[9] ‘Necessary existent’ is Avicenna’s term—wağib al-wuğud—meaning something that necessarily exists. His term for contingent things is ‘possible-in-itself.’ It is admittedly unclear if Avicenna thought that necessary entities are uncaused or cause themselves to exist. This article follows Zarepour (2022: §3.5) and takes Avicenna to think that (a) a necessary existent has an essence, and (b) a necessary existent is an uncaused entity, the essence of which guarantees it exists and depends upon nothing to continue existing. See Zarepour (2022: §3.5) for discussion of these and other details concerning how to read Avicenna’s account of a necessary existent.

[10] A subtle but important point: Avicenna distinguishes between being ‘necessary-in-itself’ or ‘necessary-through-another’. Whilst you and me contingently exist, we are, Avicenna argues, ‘necessary-through-another’ because something makes us exist and sustains our existing, since our essences do not guarantee our existence. Avicenna wants to prove that something exists that is ‘necessary-in-itself,’ which he calls a ‘necessary existent.’ Interestingly, since everything for Avicenna is either necessary-in-itself, or possible-in-itself but necessary-through-another, Avicenna maintained that everything exists necessarily (even if only one thing, which will turn out to be God, exists necessarily because of its own essence). A contemporary defender of a version of the view that everything exists necessarily, called necessitism, is Williamson (2013).

[11] On a traditional concept of God, see The Concept of God: Divine Attributes by Bailie Peterson. Also see Schlesinger (1988); Hestevold (1993), and Zarepour (2022: §2).

[12] X is a proper part of Y if X is a part of Y but not vice versa. For example, my arm is a proper part of me because my arm is a part of my body, but my body is not a part of my arm.

[13] Compare Avicenna with Anselm of Canterbury (1033/4-1109) on God’s attributes: see The Ontological Argument for the Existence of God by Andrew Chapman. Anselm thinks there is a special divine attribute, but it is not necessity: it is perfection. It is special because God’s being perfect is taken to entail that he is necessary, simple, and more (see Zarepour 2022: §2 for the Anselm-Avicenna comparison; see Nagasawa (2017) for a contemporary defense of Anselm’s view).

[14] So ‘proof’ here and throughout refers to Avicenna’s argument for at least one necessary existent, not his arguments that this necessary existent uniquely possesses the divine attributes (i.e., is God). See Adamson (2013; 2016, Ch. 18) and Zarepour (2022: §5) on how Avicenna argues that the divine attributes follow from God’s necessary existence. Of particular concern for Avicenna was establishing the uniqueness and simplicity of the necessary existent. This is because the central Islamic doctrine of tawhīd— the ‘oneness’ of God—is often interpreted as the claim that God is unique (there is exactly one God) and that God’s nature does not admit of multiplicity (that God lacks proper parts).

[15] Recall here and throughout that, since Avicenna argues elsewhere that a necessary existent would be God, ‘necessary existent’ ultimately means ‘God’ for Avicenna. But, again, the argument called his ‘proof’ is, strictly speaking, for the existence of something that exists necessarily. You could, in principle, agree that his argument demonstrates that something necessarily exists and reject his other arguments for thinking that a necessary existent would be God.

[16] Zarepour (2022: §4) identifies four argument types in Avicenna for a necessary existent (also see Morvarid 2022). They appeal variously to the idea of a necessary being and Avicenna’s account of necessity, the nature of necessitation, the impossibility of actual infinities, and the version I will present here that is found in the Metaphysics section of The Salvation (al-Nağāt, Avicenna 1985 [ca. 1030s]; see Zarepour 2022: 37–38 for a translation of the crucial passage).

[17] To be clear: Avicenna does not think that any random thing you pick—like you or me—is necessary-in-itself, since our essences do not guarantee our existence (e.g., being human does not guarantee that we are existing humans; again, recall any fictional human you like!). He is trying to show how assuming the existence of anything will lead to acknowledging the existence of at least one necessary existent, before giving independent arguments to think that if something is a necessary existent, then it has all the divine attributes.

[18] X is a whole, the parts of which are every contingently existing thing. If only one contingent thing exists, then X is a whole made up of only one part. If more than one contingent thing exists, then X is a whole where all its proper parts are things that exist contingently.

[19] It may seem strange to imagine Avicenna ending the argument there. It sounds like Avicenna would, in principle, accept that the universe—X—is God! Avicenna, however, denies that X exists necessarily. For it seems implausible that a group composed of things that only contingently exist itself exists necessarily. Remember, Avicenna also independently argues that if something is a necessary existent, then it has all the divine attributes.

[20] Avicenna claims that ‘a cause of the totality is a fortiori a cause of the existence of its parts.’ (Avicenna 1985 [ca. 1030s]: 567–8, translated by Zarepour 2022: 38). So, if some contingent entity causes the collection of all contingent things, X, to exist, then it is a cause of the existence of every contingent thing that makes up that collection—which would include itself!

[21] My reconstruction is indebted to a longer, detailed reconstruction by Zarepour (2022: §4.4.) that he calls ‘Argument D.’ Notice that no claims about infinite regresses or the impossibility of actual infinities are involved in this argument. It is worth noting that the argument is sometimes presented like this: we can ask if the cause of X’s existence is part of X or not. If it is not, then it necessarily exists, since X is the collection of all contingent things. If it is part of X, then it is contingent. But if so, then X would be causing itself to exist and that is impossible. So, the cause of X’s existence must not be a part of X. Since X just is the collection of all possible things, that means that the cause of X’s existence is a necessary existent!

[22] Each view roughly corresponds to whether the argument is an ontological or a cosmological argument, respectively. For the former view, see Morewedge (1970), Johnson (1984), and Zarepour (2022: §4.5.); for the latter, see Davidson (1987). Mayer (2001) and McGinnis (2010) think it a ‘hybrid.’ The argument might look obviously like a cosmological argument since ‘something exists’ sounds like an empirical observation. But there are reasons to think Avicenna may have thought that you could know something exists by reason alone. Avicenna could suggest that you know the claim ‘I exist’ by reason alone via his famous ‘Flying Man’ thought experiment of a man without sense perception and no experimental data, and ‘I exist’ entails ‘something exists.’ See Zarepour (2022: §4.5.) for this suggestion and related discussion.

[23] Note that Aquinas was influenced by Avicenna (see Adamson 2013). See Cosmological Arguments for the Existence of God by Thomas Metcalf, The Ontological Argument for the Existence of God by Andrew Chapman, and Modal Ontological Arguments for the Existence of God for the details of many related arguments for God’s existence.

[24] Zarepour (2022: 39–40; 2025) directly responds to the charge that Avicenna commits the fallacy of composition in his proof.

[25] Zarepour (2022: 24) calls this a version of the ‘principle of sufficient reason’ he labels ‘PSR*’: ‘every existent whose existence is not necessary in itself has a cause.’ Also see Bäck (1992) and Richardson (2014). (For discussion of the principle of sufficient reason in Leibniz, see Gottfried Wilhelm Leibniz’s Principle of Sufficient Reason by Marc Bobro). If it is false that everything that is not necessary-in-itself has a cause, then it looks like the proof fails. 

[26] Adamson (2016: 131). There are, of course, many other views of the metaphysics of modality, that is, of necessity, contingency, and possibility. The point is simply that the force of this objection depends in part on the provision of a specific, plausible account of contingency that makes sense of something existing contingently without a cause and yet without thereby being necessary.

[27] Adamson (2016: 131).

[28] In particular, this was the view of the Persian, Muslim philosopher and theologian Abu Hamid al-Ghazālī (2000 [1095]). In that book, The Incoherence of the Philosophers (Tahāfut al-Falāsifa), al-Ghazālī examines twenty doctrines associated with Avicenna and maintains that three of them—that the universe is necessarily created; that God only knows particulars ‘in a universal way’; and that only soul-based resurrection and not bodily resurrection will occur—constitute heresy in Islam. Misunderstanding the title of this book, and its contents, has created seemingly-still-pervasive myths that al-Ghazālī thought that what we call ‘philosophy’ today was incoherent, or that he somehow ended philosophy the subject in the Islamic world. These are nothing but myths. The term ‘falāsifa’ here refers to those who held a specific set of doctrines and claims and not the subject we call ‘philosophy.’ See Griffel (2021) and Hadisi (2025) for further helpful discussion.

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About the Author

Farbod Akhlaghi is Assistant Professor in Moral Philosophy at Trinity College Dublin. Previously, he was Stipendiary Junior Research Fellow in Philosophy at Christ’s College, University of Cambridge, and received his DPhil in Philosophy from the University of Oxford. His primary research interests are in moral philosophy, metaphysics, and their intersections, with wider interests including the philosophy of religion, culture, epistemology, political philosophy, meta-philosophy, and the history of philosophy. farbodakhlaghi-g.weebly.com

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