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Simple is as simple does: Plantinga and Ghazālī on divine simplicity

Published online by Cambridge University Press:  06 May 2022

Jon McGinnis*
Department of Philosophy, University of Missouri, St. Louis, One University Blvd., St. Louis, MO 63121, USA
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This study considers the notion of divine simplicity, the idea that God is not a composite of more basic features, and the criticisms by al-Ghazālī (d. 1111) and Alvin Plantinga of that doctrine. What is shown is that most of the argumentation against divine simplicity frequently credited to Plantinga had been nearly perfectly anticipated by al-Ghazālī. Moreover, in responding to a stronger form of divine simplicity, which Avicenna (d. 1037) had presented, than the Thomistic version that Plantinga attacks, Ghazālī develops ‘new’ arguments and moves that are still valuable and informative to the discussion of divine simplicity today.

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In his now classic text Does God Have a Nature, Alvin Plantinga tackles two thorny issues concerning, broadly, God's relation to properties.Footnote 1 These issues are, first, what is God's relation to his essential properties, like omnipotence and omniscience, and, second, what is God's relation to those properties that are separate from him, like the property of being prime or a horse, and indeed God's relation to abstract objects more generally. For the purposes of this study, I consider only the problem of God's relation to his essential properties, that is to say, God's relation to his own nature.

The problem as Plantinga presents it arises when we consider God's aseity and sovereignty.Footnote 2 Aseity refers to God's being wholly self-sufficient and not dependent upon anything else, while divine sovereignty is that everything else depends upon God for its existence and is under God's control. Should God have a nature, or in other words, should God have certain properties that are essential to him, it looks as if God neither creates nor has control over what those essential properties are, nor whether those properties necessarily exist nor even what the character of those properties is, for example, what it is like to be omniscient. God is wholly dependent upon those properties that make up the divine nature, and thus God's aseity is challenged. Similarly, those properties are out of God's control, and thus God's sovereignty is challenged. In short, the issue is how one should understand the relation between God's essential properties and the divine self.

The traditional answer among theologians and philosophers to this question has been an appeal to a doctrine of divine simplicity.Footnote 3 God does have a nature, but that nature is absolutely simple – the property of being God, if you will – and so, the divine nature is not a composite of disparate properties out of God's control. Moreover, God is identical with that nature, and so while God is dependent upon his nature, the dependence is an innocuous case of self-dependence. Despite the simplicity of this answer, understanding divine simplicity has turned out to be, well, not so simple. Indeed, given the very complexity of divine simplicity, Plantinga counsels rejecting the doctrine outright for two reasons, which, as we shall see, were anticipated in the medieval Islamicate world. These reasons, to which I return below, are briefly: (1) divine simplicity flies in the face of the fact that God has several properties, such as knowledge, power, will; (2) even if these apparently distinct properties reduce to a single property, then if God is identical with that property, God is a property, not a person, which seems absurd.

The question of God's relation to his properties or attributes (ṣifāt) and the rejection of the classical doctrine of simplicity is not new. The question was among the central theological issues entertained by philosophers and theologians in the medieval Islamicate world.Footnote 4 Indeed, the renowned Muslim theologian Abū Ḥāmid al-Ghazālī (d. 1111) subjects the philosophical doctrine of simplicity and the grounds for accepting it to a scathing critique, which interestingly anticipates and goes beyond Plantinga's own critique.Footnote 5

Towards hopefully enriching the contemporary discussion of divine simplicity, in this article, I present how Plantinga's discussion and critique of divine simplicity tracks the medieval Islamic discussion, specifically as it appears in the works of Ghazālī, and how the medieval accounts contribute new resources to the discussion. I begin by considering Avicenna's (d. 1037) doctrine of divine simplicity, which is arguably stronger than the position that Aquinas (d. 1274) espoused, at least as Plantinga presents it and then rejects it. Avicenna's stronger version of divine simplicity can respond to some of Plantinga's objections, albeit at the cost of certain religious sympathies. I then turn to Ghazālī's critique of Avicennan simplicity, as that critique appears both in his negative and destructive philosophical work The Incoherence of the Philosophers and in his positive and constructive theological treatise The Economy of Belief.Footnote 6

Avicenna's doctrine of divine simplicity

Plantinga begins his account by simply asking, ‘Why simplicity?’Footnote 7 He then rightly notes that for traditional theists it is fundamentally the fear that a composite God, that is, a God having distinct properties, attributes, or the like, is in some way causally dependent upon those properties. This is certainly correct. A more important issue, however, is the nature of this dependency relation. Plantinga's own reconstruction of the reason for accepting simplicity draws upon his understanding of the Thomistic theory of participation and suggests that if God were not simple, he would depend upon properties like power, wisdom, blessedness, in the order of final causation.Footnote 8 Presumably, these properties would be ends that perfect God. I shall not rehearse that reconstruction here, but turn to Avicenna's characterization of the nature of the dependency relation, which is significantly different from the account as Plantinga presents it.Footnote 9

Avicenna's argument for divine simplicity draws upon his unique modal ontology and his conception of what it would even be like for something to be the Necessary Existent through itself (wājib al-wujūd bi-dhātihi), which Avicenna identifies with God.Footnote 10 At the very least, Avicenna notes, it could not exist through anything other than itself (bi-ghayrihi). Additionally, Avicenna makes three mereological assumptions about parts and part–whole compositions. The first assumption is that if God were to have distinct properties, these properties would stand to God as parts to a whole. While not everyone wants to include abstracta, like properties, within the field of ‘part’, the objections for doing so are frequently from nominalists, and Plantinga is no nominalist.

Avicenna's second mereological assumption is that parts (or at least proper parts) taken individually are other than or different from the whole taken collectively. I assume that Plantinga would accept something like this assumption. That is because if he allows that the whole taken collectively is no different from a part taken individually, he implicitly has accepted the doctrine of simplicity, for as Plantinga notes for God to be absolutely simple is just for God's existence to be identical with his properties, like being the Necessary Existent through itself.Footnote 11

Avicenna's third mereological assumption is perhaps the most controversial (but then all composition principles are controversial). It is that wholes are causally dependent upon their parts. Here, however, unlike Aquinas, or to be exact Plantinga's Aquinas, the order of causation is not final causation (at least not in one sense)Footnote 12 but more akin to material causation, although Avicenna does not say as much explicitly. To be sure, I do not mean by material here gross, physical matter, which exists only as extended in three dimensions; rather, I am taking material in the general sense that Avicenna defines it in his Metaphysics. ‘By “material” (ʿunṣuriyya) [I mean] the cause that is a part of something's subsistence by which the thing potentially is what it is (huwa mā huwa)’ (Avicenna (2005), 6.1 [2]). Here the Arabic huwa mā huwa indicates the ‘what it is to be’ a particular thing, and so corresponds with a thing's essence or nature. Thus, a whole is causally dependent upon its parts in that the parts constitute the whole, somewhat in the way that the Axiom of Extensionality entails that a set is identical with its elements. Understood thus, I take there to be some reason for Plantinga to accept a version of Avicenna's third mereological assumption.

Give these three assumptions, and particularly the second and the third, Avicenna argues for the simplicity of the Necessary Existent through itself like this.Footnote 13 It is simply a contradiction for something to exist both through itself and through another; it is tantamount to saying that something's existence depends on nothing and depends on something. Now, if the Necessary Existent through itself were a composite of properties, those properties are parts that constitute the whole of what it is to be the Necessary Existent through itself (from the first and the third assumptions); however, the parts are other than the whole (from the second assumption). Thus, the Necessary Existent through itself as a whole exists through something other than itself, namely, through its parts. Consequently, the whole of the Necessary Existent through itself exists both through itself (by definition) and through another (its parts), but we said that to exist through oneself and through another is a contradiction. Therefore, the Necessary Existent through itself, that is, God, cannot be a composite and if he is not a composite yet he exists, God's existence is simple.

Given divine simplicity, Avicenna subsequently maintains that God's sole property – which in fact is identical with God's self (dhāt) and so perhaps not strictly a property – is necessary existence through itself.Footnote 14 Every other property purportedly ascribed to God – whether it be knowledge, power, goodness, immateriality, etc. – is in fact either just another way of describing necessary existence through itself or some negation (salb) or some relation (iḍāfa) said of God.Footnote 15 Different negative and relative properties can be ascribed of God, Avicenna asserts, because they do not entail differences or multiplicity in God; they preserve divine simplicity. In the case of negative attributions, Avicenna's point is clear enough: one is merely saying that such and such a property does not exist in God. I shall say no more about negative properties, since Plantinga himself does not broach the subject and instead I turn to relational properties.

Concerning relational properties, Plantinga begins by first arguing that God has accidental properties, which seem to correspond to Avicennan relational properties.Footnote 16 As I have noted, Avicenna believes that relational properties do not threaten divine simplicity, whereas Plantinga thinks that they do. Why? For Avicenna, purportedly relational properties are not really properties at all, at least not in the sense of constitutive features. While Plantinga is willing to grant that relations need not be properties, they are, he insists, characterizations, which God may or may not have had. Moreover, maintains Plantinga, possessing a given characterization does make God ‘different from what he would have been had it not characterized him’ (Plantinga (Reference Plantinga1980), 43). Plantinga's examples of such accidental characterizations are creating Adam and knowing Adam sinned, which happen to be paradigmatic relational properties in Avicenna's own discussion.

Plantinga's point is well noted. It is thus worth mentioning a distinction that medieval Islamicate philosophers and theologians made when considering relational properties. That is the distinction between properties that characterize the divine person or self (dhāt), that is, those that are essential to God, and those that characterize God's action (fiʿl), or more precisely God's action relative to the effects it produces, that is, those properties that are relational or accidental. Both sides in the medieval debate agreed that God's ultimately numerous different actions or effects can be traced back to God;Footnote 17 however, they also insisted that those different effects of his action need not emanate from different essential properties or even necessarily from different ways of characterizing God. Maimonides gives the classic example that fire both bleaches and blackens, as well as both hardens and melts and does so in virtue of a single power within it; any differences in characterization are wholly owing to differences in the things affected, not fire.Footnote 18 In short, for these thinkers God's self does not have different characterizations, as Plantinga maintains; rather, his action relative to its effects have different characterizations. Thus, Plantinga's shift from properties to characteristics need not show that there are real differences within the divinity.

Moreover, Avicenna anticipates Plantinga's own examples of creating and knowing, and explicitly argues that God's knowledge of a thing is the ultimate cause of that thing's existence.Footnote 19 In other words, according to Avicenna for God to know the world, which includes Adam, is for God to create the world, which includes Adam. Knowing and creating are identical in God. The apparent differences in characterizations arises from assuming that God's mode of knowing is similar to our mode of knowing. In the case of humans, knowing is a type of potentiality we have, whereas on the traditional view of God, God is devoid of all potentiality and instead God is fully actual. Thus, God simply could not have any potential properties, like potentially knowing or not knowing that Adam would sin. Instead, any property or properties that God has must be actual.

This last point about potentiality and actuality leads to Plantinga's next move against divine simplicity. He challenges the claim that God has no potential properties, which he subsequently acquires.Footnote 20 For instance, a hundred years ago God did not have the property of being the creator of Alvin Plantinga, but now God has that property. A hundred years ago it was a potential property of God, which God subsequently acquired. Much of Plantinga's subsequent discussion of this point involves questioning the traditionalists' response that God is atemporal and outside time, which I shall not consider here.Footnote 21 Instead, I want to explore Plantinga's initial intuition for claiming that God has potential properties. The reason he gives for holding his preferred position is ‘it seems right to think that there are characteristics [God] lacks but could have had. It is natural to think, furthermore, that among these there are some he hasn't yet acquired but could acquire’ (Plantinga (Reference Plantinga1980), 44).

Given Plantinga's subsequent challenge to the traditionalists' assumption about God's relation to time, at least in Does God Have a Nature, he seems to understand ‘potential property’ in terms of temporal frequency: x has some potential property, P, just in case there is a time t1 when x does not possess P, and then some subsequent time t2 when x does possess P.Footnote 22 There is, however, another way to analyse potential properties that does not appeal to temporal frequency nor necessarily puts God in time, one that is at the fore of Ghazālī's own view of God's nature.

Ghazālī insists that all of God's relational properties involve God's volition, and that volition must involve choosing among different possible options.Footnote 23 Thus, in one sense relational properties are potential properties, if potential is taken in the general sense of being such that it may or may not be exemplified, that is, it is not necessary. Even if it is timelessly true that God wills that Alvin Plantinga comes to exist at some given time in history, presumably God likewise may have timelessly not willed that Plantinga come to exist. In modern jargon, there are possible worlds where God does not create Plantinga, so God must have some characteristics that are not necessary but merely possible, and while potentiality and possibility may not be identical, they are related. Moreover, there is a real difference in God's very self rather than merely his action, if in one possible world God has a will to create Plantinga and in another possible world God does not have that will.

Avicenna had anticipated this strategy and responded. In effect, he bites the proverbial bullet. For Avicenna, what proceeds from God does so of necessity.Footnote 24 The created order could not be otherwise than it is, for all of creation is just an overflowing of the order of the good that is God, according to Avicenna. Despite the necessity of this creative act, Avicenna maintains that creation nonetheless proceeds from God by volition.Footnote 25 Of course, Avicenna's conception of volition is not that of a free-will libertarian, which involves choosing among options. Instead for Avicenna an action is free if, (1) that action is not forced as a result of something outside of the agent; (2) the agent recognizes that it is the source of its action; (3) the agent is content with and/or consents to (riḍan) the action. Since Avicenna believes all three of these conditions are met in the divine creative act, it is, by his lights then, a free and volitional act on the part of the divinity.

I suspect that, for many, this conception of free will will raise an eyebrow. It certainly did for Ghazālī and other theologians, who thought it so eviscerated the notion of will as to make God compelled, even if by his nature, and so not truly sovereign.Footnote 26 Still in defence of Avicenna, God's not acting other than his nature allows seem no different from the fact that Plantinga and I cannot act other than as human on account of our nature. Even if Plantinga and I can act like beasts and not live up to our full perfections, it is hardly a perfection of God that God should choose not live up to the full perfection of the divine nature.

Ghazālī's critique of Avicennan simplicity

This, then, is the view of simplicity to which Ghazālī must respond: God purportedly must be simple, otherwise he is causally dependent upon his parts by way of material causality, and so his aseity is challenged. Moreover, given this view of simplicity, all of the traditional properties associated with the deity are either simply ways of speaking of necessary existence through itself or are either negative or relative descriptions of necessary existence through itself. Consequently, God's existence is in every way necessary, and this necessity extends even to the divine creative act. In the remainder of this study, I comment what Ghazālī has to say in The Incoherence of the Philosophers against the philosophers' doctrine of simplicity, supplementing it occasionally with material from The Economy of Belief. Ghazālī's critique in The Incoherence moves roughly in two steps. The first step is to undercut the Avicennan arguments for divine simplicity, while the second is to attack directly the cogency and religious satisfactoriness of the doctrine.

Ghazālī's first step begins with his response to the question of whether a deity who has multiple attributes or properties, understood as parts, needs causally depend upon those parts. Avicenna's argument again is that God is the Necessary Existent through itself. If the Necessary Existent through itself were a whole composed of parts, it would be dependent upon those parts, since wholes exist through their parts. Parts, however, are other than the whole. Thus, the whole Necessary Existent through itself would be necessary through itself and necessary through another, namely, its parts, which is a contradiction.

Ghazālī's response to this argument is threefold.Footnote 27 First, he recasts the description of God's relation to his attributes or properties in terms of a self and attributes that characterize that self rather than in terms of a whole constituted by its parts. Second, he questions whether the Aristotelian notion of material causation is a genuine form of causation or just a term of art. In effect, as we shall see, Ghazālī suggests that the relation between the divine self and its attributes is a grounding relation rather than a causal relation. Third, he counsels doing away with describing God as the Necessary Existent through itself, since the most important description is that the divine is the eternally uncaused cause of everything else. Let us take each point in turn.

Avicenna had framed the discussion of the Necessary Existent through itself in terms of whole (jumla) and parts (ajzāʾ). In contrast, Ghazālī shifts the language of the discussion to that of a self (dhāt) and the attributes (ṣifāt) that characterize that self. The shift in language, while standard among Ashʿarite theologians, also gives Ghazālī a rhetorical advantage.Footnote 28 While in Arabic there is no single term that captures the full theological, legal, and sociological scope of the English term ‘person’, there are terms which, within the proper context, certainly evoke the notion of person. Said within the context of a rational agent, dhāt is decidedly one of those terms. The advantage of this shift is that one is no longer being asked to think about an impersonal whole–part composite when thinking of the deity, but about the characteristics of a person. Moreover, while one can concede that a whole's existence is dependent upon its parts in a way that the parts need not be dependent upon the whole, one's self and the attributes that characterize one's self do not seem to share the same dependence relation as wholes and parts. In The Incoherence, Ghazālī notes that all attributes must characterize something, that is, they are characterizations of a self or person, while in The Economy of Belief, he notes that every self or person has some characterization beyond merely being a self.Footnote 29 In other words, there is a reciprocal dependency relation between selves (or persons) and their characterizations, which is not obviously true of wholes and their parts.

This last point about dependency relations leads to the second part of Ghazālī's response to Avicenna. Avicenna had claimed that a complex God, who is a whole constituted of parts, would be causally dependent up those parts since he exists through those parts and needs those parts. God's aseity thus seems jeopardized. Ghazālī, like Plantinga after him, absolutely insists on God's aseity: God is absolutely uncaused and eternal. The issue for Ghazālī, instead, is what counts as a cause or causal dependency (ʿilla) as opposed to being grounded in another.

Ghazālī concedes that God's attributes need the divine self or person precisely as that which they characterize, whether that characterization is being a necessary existent, having power, knowing, willing, etc. Still, he continues, the fact that God's attributes need or are grounded in the divine self does not necessarily entail a causal relation between the two, certainly not in the sense of an efficient cause (ʿilla fāʿiliyya).Footnote 30 Here presumably Ghazālī intends Avicenna's own account of an efficient cause: x is an efficient cause of y just in case (1) x is extrinsic to y and (2) y has its existence from x.Footnote 31 Ghazālī then observes that there is nothing obviously impossible about the divine person and the set of attributes that characterize him both being eternal and uncaused, and so not having their existence from some extrinsic agent.Footnote 32 In that case, neither of them would have an efficient cause nor would the divine person or the set of attributes be the efficient cause of the other.Footnote 33

Ghazālī next turns to the charge that a relation of material causation exists between the two, for the divine self is that which is receptive of the attributes in the way that matter is receptive of form.Footnote 34 He responds by first observing that ‘receptive (or material) cause’ (ʿilla qābiliyya) is a technical term among the philosophers but is not thought of as a cause in normal parlance. More commonly, asserts Ghazālī, causation is associated with efficient causation, and we have seen that that form of causation does not hold here. Instead, claims Ghazālī, what is receptive (qābil) or the receptacle (maḥall) is merely that in which a series of attributes terminates, for there cannot be an actually infinite series of attributes (even for God).Footnote 35 For Ghazālī, there simply is no causation here anymore than a point that terminates a line would be a cause of the line. Instead, Ghazālī sees the relation between God's attributes and his self as a grounding relation (muḥtāj ilā ghayrihi, literally ‘what needs another’).Footnote 36

Of course, in this case there is a sense in which God's attributes need a receptacle in which to exist, namely, the divine self, and, conversely, that for God's self to be perfect, he needs the divine attributes. Thus, one might object that given that God is the Necessary Existent through itself, God cannot need anything for his existence and perfection. If God needs anything, then he is not absolutely self-sufficient (lā ghanīyan muṭlaqan) and so again his aseity seems jeopardized.Footnote 37 Ghazālī dismisses the objection as mere rhetorical flourish playing to the crowd. To say that one needs precisely that which one already possesses, and possesses inseparably and eternally, is just to be obtuse. It is equivalent, he thinks, to saying that a rich man is needy and in want because he needs his money in order to be rich, but of course the rich man is not needy and in want when he in fact possesses his wealth. As for God, divine self-sufficiency means nothing other than ‘the existence in himself of the attributes that negate need’ (Ghazālī (Reference Ghazālī2000b) discussion 6 [18]). It is in virtue of possessing all perfections that God is self-sufficient and neither his existence nor perfection are through another, in the sense of depending upon an efficient cause.

In the end, Ghazālī thinks that Avicenna's entire argument for divine simplicity rests on characterizing God as the Necessary Existent through itself. There appears to be an element of truth here. Avicenna indeed leans heavily on the through itself/though another (bi-dhātihi/bi-ghayrihi) distinction to argue for divine simplicity. The distinction also seems implicitly to assume that through means being causally dependent upon. If, however, there is a real distinction between a causal relation and a grounding relation, as Ghazālī claims, then to say that if God is not simple, he exists through himself and through another, namely, his parts, is potentially equivocal. Since for Ghazālī all the phrase, ‘Necessary Existent through itself’ means is an existent that is eternal and has no efficient cause for its existence, he counsels forgoing the language of ‘Necessary Existent through itself’ altogether, precisely because it can be misleading.Footnote 38 This completes the first step of his critique.

In the second step, Ghazālī is no longer on the defence but now on the offense and suggests that the doctrine of divine simplicity is simply incoherent. Again, the general doctrine is that there are no distinctions whatsoever within God. All the properties attributed to God really just are necessary existence or some negation of or relation to necessary existence. Ghazālī presents three arguments against the doctrine. Two of his arguments perfectly anticipate what Plantinga dubs the ‘substantial’ and ‘monumental’ difficulties with the doctrine of divine simplicity.Footnote 39 Ghazālī's third argument involves the distinction between God's self and his action, which we encountered when considering medieval responses to Plantinga's argument that God must have both essential and accidental properties. Interestingly, Ghazālī turns the distinction between God's self and his action against divine simplicity. Before considering Ghazālī's ‘new’ argument, let me begin with his riffs on Plantinga's substantial and monumental difficulties.

Plantinga identifies the ‘substantial’ difficulty as this:‘If God is identical with each of his properties, then each of his properties is identical with each of his properties, so that God has but one property. This seems flatly incompatible with the obvious fact that God has several properties’ (Plantinga (Reference Plantinga1980) 47). The difficulty is clear enough: we want and do attribute different seemingly positive and distinct properties of God – God has knowledge, God has power, God has will, etc. – however, God cannot have different positive distinct properties if God is absolutely simple. Seemingly, we must jettison either divine simplicity or our religious sensitivities and practices when talking about God.

Ghazālī shares the same view and brings it to the fore in his The Economy of Belief.Footnote 40 Such attributions as existing necessarily, knowing, willing, etc. all have different accounts, meanings, or senses (maʿānin) observes Ghazālī. To say that the account of all the divine predications is one and the same for all, like the sense or meaning of Avicenna's necessary existence in itself, is simply to fly in the face of this bit of common sense. Moreover, and here Ghazālī goes beyond Plantinga, the philosophers' conception of divine simplicity renders all knowledge of God empty or tautological. To say ‘God is God’ or ‘God is himself’ tells us nothing about God. In contrast, to learn that God is the Necessary Existent through itself is to learn something more or additional (zāʾid) about God. Additionally, if all the seemingly positive properties attributed to God simply are just ways of talking about one and the same thing, then Ghazālī complains:

Is what is understood by our saying ‘powerful’ the same as what is understood by our saying ‘knower’ or is it different from it? If it is exactly the same, then it would be as if we said that God is powerful powerful, which is sheer redundancy. If it is different, then that is what is desired. (Ghazālī (Reference Ghazālī2004, Reference Ghazālī2013), 2.2.1)

Given divine simplicity, maintains Ghazālī, all theological claims, in effect, are tautological truisms. Once we have a trivial bit of theological knowledge (expressed by ‘God is God’), we thereby know everything that is to be known about God. Instead of charging Avicenna with theological scepticism, Ghazālī charges him with endorsing theological omniscience.

The second problem that Ghazālī finds with the philosophers' conception of divine simplicity is what Plantinga dubbed the ‘monumental’ difficulty. Ghazālī himself puts the concern this way:

[The philosophers] were not content to deny of the First [i.e. God] the rest of the attributes nor to deny of him a true nature and quiddity such that self-subsistence is also denied of him, but reduced him to the true natures of accidents and attributes that have no self-subsistence. (Ghazālī (Reference Ghazālī2000b), discussion 6 [54])

The monumental issue, as Ghazālī sees it, is that the philosophers have denied that in the case of God there is some self or person that has the attribute or property of being the Necessary Existent; rather, God is identical with this single property. Consequently, God simply is an attribute or property, and a property or attribute hardly seems to be an object of worship, let alone something that would count as God. As Plantinga puts it, ‘if God is a property, then he isn't a person but a mere abstract object; he has no knowledge, awareness, power, love or life’ (Plantinga (Reference Plantinga1980) 47). Ghazālī wholly concurs.

In addition to having anticipated Plantinga's two difficulties, Ghazālī identifies a third difficulty, which applies to any classical theist who maintains both the doctrines of divine simplicity and God's omniscience. Ghazālī's argument begins with the following question: Does God know things other than himself? Ghazālī realizes that there are philosophers, such as Aristotle (Metaphysics Λ (XII), 9), who deny that God knows anything other than himself. To these philosophers Ghazālī simply says, ‘Shame on you!’ (nāhīkum khiziyan) (Ghazālī (Reference Ghazālī2000b) discussion 6 [48]). Such a view entails that the knowledge of creatures is greater than God's, for creatures not only know themselves, but they additionally know others as well. Consequently, in God, who is supposedly perfect, there is ignorance of the world, but ignorance is an imperfection. Thus, what is purportedly most perfect and without imperfection is imperfect, a contradiction. In the end, Ghazālī remarks, ‘what difference is there between him and the dead, except his knowledge of himself’ (Ghazālī (Reference Ghazālī2000b), discussion 6 [49]).

If, conversely, one asserts that God knows things other than himself, as Avicenna did,Footnote 41 then, claims Ghazālī, one implicitly has given up divine simplicity. That is because the knowledge of oneself is distinct and different from the knowledge of another. For Ghazālī this claim is just self-evidently obvious. Consequently, within God there are at least two distinct things, namely, his knowledge of himself and additionally his knowledge of the other, that is, the world. Avicenna had attempted to avoid this conclusion by saying that God's knowledge of others is identical with his knowledge of himself.Footnote 42 That is because, as absolutely perfect, God's knowledge of himself must be absolutely perfect. Since he is the cause of the world, he must absolutely perfectly know himself as the cause of the world; however, to know a cause absolutely perfectly is to know the effects of that cause, which in the case of God again just is the world. Thus, God knows the world simply through his absolute and perfect knowledge of himself as cause.

Ghazālī responds: causation involves a relation (iḍāfa), namely, between the cause and the effect.Footnote 43 Consequently, if God knows that he is the cause, continues Ghazālī, he likewise must know this relation. Now the relata that go into a relation are other than the relation itself. Thus, for God to know himself, that is, one of the relata, and to know that this causal relation exists again requires that within God there are at least two distinct things, namely, God's knowledge of himself and additionally his knowledge of this causal relation.

Ghazālī further motivates this distinction between the divine self and its causal relation to the world by having us imagine ourselves and our being caused, and so being related to another. He notes that it is possible for one to know oneself without also knowing any other, and so not knowing one's relation of being caused. In contrast, it is impossible, indeed a contradiction, for one to know oneself without also knowing oneself. Now the possible is different from the impossible, and so knowledge of the self and knowledge of the self's relation to another must be different. This difference remains, continues Ghazālī, even if the relation is one of being the cause of another rather than being caused by another, and so it applies equally to God's knowledge of himself as cause. Consequently, if God knows that he is causing – and recall that Avicenna's own account of divine volition required that God does know that he is acting – and God's causing is different from God, as Ghazālī believes he has shown, there must be multiplicity in the divine knowledge. God's knowledge, however, is purportedly identical with the divinity itself, and consequently there is multiplicity in God. In short, concludes Ghazālī, divine simplicity is incompatible with God's omniscience. For Ghazālī, if one must decide between the two, the decision is obvious: anything worthy of the title God must be omniscient, whereas it is not at all obvious that it must be simple.


With this last argument I conclude. On the historical side, much of the argumentation against divine simplicity credited to Plantinga and other contemporary philosophers of religion, had been anticipated and developed by Ghazālī in interesting ways nearly a thousand years earlier. On the philosophical side, I simply note that much of what Avicenna and Ghazālī have to say about divine simplicity is still philosophically relevant today and can, and indeed should, inform the contemporary discussion among philosophers of religion. Finally, it is important to note that the initial problems for which simplicity was put forth still remain: what is the relation between God's essential properties and his aseity and sovereignty, if God is not absolutely simple? It appears that God neither creates nor has control over his essential properties, nor whether those properties necessarily exist nor even what the character of those properties is. Until these issues are resolved, I fear, understanding the divine nature is not simply as simple as rejecting simplicity.


I am grateful to Billy Dunaway and Hashim Morvarid for discussions and comments on an earlier version of this article. I also want to thank two anonymous Religious Studies referees for their insightful comments and suggestions. Finally, I wish to acknowledge the generous support of the John Templeton Foundation, which allowed me to do the research for this article.


1. Does God Have a Nature has created its own cottage industry of criticisms and defences. The following is only a very limited sampling of that literature, primarily with an eye to divine simplicity: Byerly (Reference Byerly2012), Dewan (Reference Dewan1989), Leftow (Reference Leftow2006), Mann (Reference Mann1982), and Stump (Reference Stump1983).

2. Plantinga (Reference Plantinga1980), 1–10.

3. Augustine (1955), XI, 10, Avicenna (2005) 8.4–5 and Thomas Aquinas (Reference Aquinas2012), ST I q. 3, aa3–4.

4. Classic studies of the debate in the medieval Islamicate world of the divine attributes include Wolfson (Reference Wolfson1976), ch. 2, Frank (Reference Frank1978), Gimaret (Reference Gimaret1990), II, 3–6, and Rudolph (Reference Rudolph1997), 8.2.5.

5. Ghazālī (Reference Ghazālī2000b), discussions 5–8 and Ghazālī (Reference Ghazālī2004, Reference Ghazālī2013), treatise II, especially part 2; I give subsequent references to ‘Ghazālī (Reference Ghazālī2004 Reference Ghazālī2013)’ in capital roman numerals for ‘treatise’, Arabic numeral for ‘part’, and lower-case roman numeral for subsection. For contemporary discussions of Ghazālī's views on divine simplicity see Moad (Reference Moad2015) and Martin (Reference Martin2017).

6. It should be noted that these two works both come from an earlier period of Ghazālī's life before his ‘spiritual crisis’, which led him to embrace Sufism and to compose works that are frequently more Avicennan in character. For Ghazālī's autobiography and his own account of his religious crisis see Ghazālī (Reference Ghazālī2000a); for the ground-breaking studies on Ghazālī's Avicennism see Frank (Reference Frank1992) and Idem (Reference Frank1994).

7. Plantinga (Reference Plantinga1980), 28.

8. Ibid., 30–32.

9. While I am hesitant to say that Avicenna has a stronger conception of simplicity than Aquinas himself (see ST pars 1, q. 3), rather than Plantinga's Aquinas, Thomas is committed to there being a plurality of persons within God (see ST pars I, qq. 30–31), which at least at first blush appears inconsistent with Avicenna's conception of simplicity. Still, without a careful comparison of Aquinas' views on the Trinity with those of Avicenna on simplicity (which is well beyond the scope of the present article) I remain agnostic on this issue.

10. Avicenna (2005), 1.6–7 and Idem (1985), ‘metaphysics’, 2.1–5 and 12–13 with translations in McGinnis and Reisman (Reference McGinnis and Reisman2007), 211–216.

11. Plantinga (Reference Plantinga1980), 27.

12. At Avicenna (2009) 1.10 [7], he does say that in composites the parts are for the sake of the composite, in which case the composite or whole is the parts' end or final cause. Compare this understanding with Plantinga's interpretation of Thomas' theory of participation, whereby God's individual properties apparently are the final cause for God's having a property or properties; see Plantinga (Reference Plantinga1980), 31–32.

13. Avicenna (2005), 1.6–7, Idem (1985), ‘metaphysics’, 2.4–5 with translation in McGinnis and Reisman (Reference McGinnis and Reisman2007), 213–214.

14. A frequent translation of dhāt among Islamicists is ‘essence’. There are reasons for avoiding that translation, at least as applied to the use of dhāt during the classical period of Islamic philosophy and theology. Richard Frank argued that at most dhāt might refer to an individual essence, more like a haecceity, indicating the existence of the thing, but certainly not in the broad sense of essence as in animality or humanity (Frank (Reference Frank1999, Reference Frank, Morélon and Hasnawi2004)). Frank counselled rendering dhāt either ‘entity’ or even preferably as the pronoun – which is exactly what it is – like auto in Greek. (The exception is in prepositional phrases used adverbially, like bi-dhāt, ‘essentially’ which like kath’ hauto in Greek or per se in Latin is often translated ‘essentially’, yet neither heauto nor se is rendered ‘essence’.) Frank's advice is sage particularly when presenting medieval Islamicate thought to contemporary analytic philosophers, where an essence is usually understood as a necessary and unique property (cf. Plantinga (Reference Plantinga2003), 78–79, 140), whereas for our medieval Muslim thinkers dhāt is decidedly not a property but the bearer of properties.

15. Avicenna (2005), 8.4 [2].

16. Plantinga (Reference Plantinga1980), 39–44.

17. Here a qualification is necessary. For Avicenna, from God only one immediate effect proceeds – ‘from the One only one proceeds’ (Avicenna (2005) 9.4 [5]) – however, from that one effect, which is an immaterial intellect, a plethora of effects cascade, all of which are ultimately dependent on God for their conservation and their continued existence at every moment that they exist. For a discussion of the principle ‘from the one, only one proceeds’ and its subsequent reception in the Islamicate worlds, see Amin (Reference Amin2020).

18. Maimonides (Reference Maimonide2010) I.53, with translation in Idem (Reference Maimonides1963), vol. 1, p. 120.

19. Avicenna (2005), 8.7.

20. Plantinga (Reference Plantinga1980), 44–46.

21. The question of God's relation to time was another hotly debated issue in the medieval Islamicate world. One reason put forth by both theologians and philosophers alike for thinking that God must essentially be outside time is that time itself is part of the created order. Add to this thought that of certain theologians, namely that whatever has been created must have been created at some first point in time in the finite past. Consequently, God considered independent of creation, must be outside of time, or at the very least God can/does exist when there is no time. Unfortunately, in English we cannot speak of God's existence independent of creation without introducing tense and temporal particles, like ‘before’, ‘prior to’, and the like, which are not necessarily required when discussing this issue in Arabic. For a contemporary discussion of God's relation to time see Craig (Reference Craig2001).

22. I am not suggesting that Plantinga does not have other resources beyond appealing to temporal frequencies to explain potential properties. He does. Must obvious is his notion of possible worlds understood in terms of maximal sets of compossible propositions – world books; see, for example, Plantinga (Reference Plantinga1970) and Idem (Reference Plantinga1976). Thus, while God as a necessary being would exist in every possible world, God's accidental properties would be different contingent upon which world book characterizes a given possible world. Still, in On Does God Have a Nature, Plantinga does not avail himself of these sources, and instead appeals exclusively to properties that God is yet to have, now has or will have, all temporal indicators.

23. See Ghazālī (Reference Ghazālī2000b), discussions 1 [41–64] and 11; and Idem (Reference Ghazālī2004, Reference Ghazālī2013), II.1.iv, ‘on will’.

24. The issue of whether Avicenna was a determinist, compatibilist, or otherwise is a vexed one in the literature; for the historiography and a discussion see Ruffus and McGinnis (Reference Ruffus and McGinnis2015).

25. Avicenna (2005), 9.4 [2–4].

26. At Ghazālī (Reference Ghazālī2000b), discussion 3, he raises his concerns, which almost exactly anticipate the so-called ‘modal collapse argument’, which purports to show that divine simplicity entails that everything exists necessarily. Contemporary versions of the objection can be found in Moreland and Craig (Reference Moreland and Craig2003), 525 and Mullins (Reference Mullins2013). Recently, Christopher Tomaszewski (Reference Tomaszewski2019), followed by Joseph Schmid (Reference Schmid2022), have questioned the logical validity of the argument, claiming that it involves an invalid substitution into a modal context.

27. Ghazālī (Reference Ghazālī2000b), discussion 6 [3–12].

28. While Ghazālī's shift in language does give him a rhetorical advantage, it also potentially begs the question against Avicenna. In effect, Ghazālī's reformulation smuggles in the suggestion that the reciprocal dependence of self and characterizations is innocuous, whereas Avicenna's aim is to show that there is one self or entity (dhāt) that is free of any dependence, other than perhaps the trivial property of self-dependence. Thus, the issue is whether the reciprocal dependence of self and characterizations poses a threat to divine aseity: Ghazālī believes no; Avicenna believes yes. I am grateful to an anonymous reviewer for this observation.

29. Ghazālī (Reference Ghazālī2000b), discussion 6 [7 and 12]; and Idem (Reference Ghazālī2004, Reference Ghazālī2013) II.2.i.

30. Ghazālī (Reference Ghazālī2000b), discussions 5 [5–7] and 6 [8].

31. Avicenna (1985), ‘metaphysics’, 1.12, translation in McGinnis and Reisman (Reference McGinnis and Reisman2007), 209.

32. Ghazālī (Reference Ghazālī2000b), discussion 6 [8].

33. One might argue that if God is a composite of a self and attributes, then there must be a cause that provides composition to the divine self and its attributes, and so explains God's unity as well as all of God's attributes' acting in a unified way. In such a case, this unifying cause might appear equivalent to an efficient cause. Ghazālī's response is that to be an existent just is to be a unity. Existence is co-extensive with unity. Thus, just as God's self and the attributes predicated of that self are co-eternal and uncaused, so is their unification. In short, no additional cause is needed to explain God's unity; Ghazālī (Reference Ghazālī2000b), discussion 6 [19–20].

34. Ghazālī (Reference Ghazālī2000b), discussion 6 [8–12].

35. Ibid. [11–12].

36. Ibid. [18].

37. Ibid.

38. Ibid. [10]. It is worth noting that unlike Avicenna who was a modal realist and believed that there are things in the world that have de re possibilities and necessities, Ghazālī, at least in the Incoherence, suggests that modal notions should be understood in terms of de dicto propositions and as such need not be grounded in existents in the world; see Ghazālī (Reference Ghazālī2000b) discussion 1 [116–119]. Thus, according to Ghazālī, a proposition (qaḍāʾ), ‘Fx’, is possible (mumkin) just in case the intellect does not resist supposing, ‘F applies to x’ (regardless of whether or not x exists); it is impossible (mustaḥīl) if the intellect resists, ‘F applies to x’; and it is necessary (wājib) if it resists ‘F does not apply to x.’ Consequently, for Ghazālī, while one can say, ‘“God exists eternally” is necessary’ or ‘“God does not have an efficient cause” is necessary’, to say, ‘God is necessary’ would be for him ill-formed at best and simply incoherent at worse, since in the latter case, there is no proposition about God over which the modal operator ranges. Such a concern would again explain Ghazālī's shift from the Avicennan language of describing God as the Necessary through itself, to Ghazālī's own preferred language of the eternal and uncauses. I am grateful to an anonymous referee for suggesting a similar point, albeit they ascribed to Ghazālī a temporal frequency modal of modalities.

39. Plantinga (Reference Plantinga1980), 47.

41. Avicenna (1985), ‘metaphysics’, 2.18–19, translation in McGinnis and Reisman (Reference McGinnis and Reisman2007), 216–219 and Avicenna (2005), 8.6–7.

42. Ibid.

43. Ghazālī (Reference Ghazālī2000b), discussion 6 [29].


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