In his Does God have a Nature, Alvin Plantinga aims to explore three interrelated questions: (i) does God have a nature? (ii) if so, is there a conflict between God's sovereignty and his having a nature? and (iii) how is God related to such abstract objects as properties and propositions? It seems clear from the introduction of the book, however, that his main and primary concern is to support two Divine widely accepted attributes namely God's aseity and sovereignty. The former is defined as God's uncreatedness, self-sufficiency and independence of everything else and the latter is described as His control over all things and the dependence of all else on his creative and sustaining activity (pages 1–2) As Plantinga puts it in one of the footnotes of the book (and much more detailed in his book The Nature of Necessity) what is meant here by the ‘nature’ of a given object is ‘a conjunctive property, including as conjuncts just those properties essential to that object.’ (page 7, note 1) According to this definition, we should notice that the nature of an object is nothing but a certain essential property. Moreover, for a great number of analytic philosophers including Plantinga essentiality implies necessity in the sense that an essential property of an object is one it possesses necessarily so that the object could never lack it. Thus an essential property is a necessary one. Using the possible world terminology, Plantinga is ready to define an essential property as follows:

But God is a necessary being in the sense that He exists in all possible worlds. Therefore, If God had a nature He has it in all possible worlds and could never lack it and this, in its turn, means that God's having his own nature is in no way up to Him. So one may conclude that God's having a nature implies that there is a thing (i.e. His nature) which is beyond His control and this clearly seems incompatible with His assumed sovereignty.

Furthermore, if we together with a group of analytic philosophers believe in the contemporary Platonic view of abstract necessary objects, the doctrine of Divine sovereignty will be threatened in another way. According to this view, beside concrete entities like physical objects, there are abstract entities such as numbers, propositions, properties, sets and state of affairs. All of these abstract entities are necessary beings existing in all possible worlds. They lack any spatio-temporal as well as causal relations so that an abstract object is neither a cause nor an effect. Therefore, if we accept that there are really abstract objects which are not caused by God, then it seems again that we are bound to reject Divine Sovereignty in the above sense since these objects are independent of God and God lacks any control over them.

As I understand Plantinga here, the main problem could be summarized as follows: the existence of entities (like God's essential properties as well as abstract objects such as properties and state of affairs) which seem to be beyond God's control is apparently incompatible with Divine sovereignty.

In the next chapters of his book, Plantinga examines four proposed solutions for the mentioned problem which respectively are (i) our concepts’ not being applicable to God; (ii) God's being identical with His nature; (iii) nominalism and (iv) universal possibilism. Explicating each of these solutions in a separate chapter, he criticizes all of them and tries to show that none of them are reasonable. Plantinga's own solution is that God has a nature distinct from and not identical with him while His lack of control over His nature and other abstract objects is not incompatible with the principle of God's sovereignty given that we have a proper interpretation of it.

What I am concerned with in this paper is Plantinga's objection to the second solution which he attributes to Thomas Aquinas. First of all, it would better to present a brief outline of Aquinas’ view.

In his Summa Contra Gentiles, Aquinas discusses Divine simplicity after arguing for a couple of other Divine attributes such as eternality. In the Summa Theologiae he apparently comes to recognize the unique theological status of the doctrine of Divine Simplicity and thus discusses it immediately after the article devoted to the arguments for the existence of God and prior to his discussion on other attributes. Aquinas develops the issue of Divine Simplicity during eight articles.

In the third article he argues for the claim that God's essence or nature is identical with him. His argument can be summarized as follows: All beings not composed of matter and form are identical with their essences or natures. God is not composed of matter and form. Therefore, God is identical with his essence or nature. (Aquinas argues for the first or major premise in the same article – namely, the third article – whereas the second or minor premise is established in the previous article.) In the end, he concludes that ‘[s]ince God then is not composed of matter and form, He must be His own Godhead, His own Life, and whatever else is thus predicated of Him.’ (ST)

Plantinga makes some objections to this part of Aquinas’ view of Divine Simplicity. First he says that God's identity with his essence and essential properties such as knowledge, power and life leads to the unreasonable result that God would not have more than one property. For ‘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; he has both power and mercifulness, say, neither of which is identical with the other.’ (Does God Have a Nature, page 47)

We may recap Plantinga's first objection in the form of the following conditional syllogism using the rule of modus tollens:

1. 1. If God is identical with his properties, then he will have just one property.

2. 2. But it is not the case that God has just one property.

3. 3. God is not identical with his properties.

We may justify the truth of the first premise, the conditional, in accordance to the principle that the relation of identity is an equivalence one in the sense that it is reflexive, asymmetric and transitive.

The second premise seems quite controversial. Plantinga considers this as an ‘obvious fact’ that God has several properties. My short reply here is that what he means by this obvious multiplicity is either a conceptual or an external one. What I mean by ‘conceptual multiplicity’ is that the concepts of Divine properties are distinct concepts in our minds so that for example the concept of ‘God's power’ is distinct from the concept of ‘God's mercifulness’. By ‘external multiplicity’ I mean that Divine properties are distinct real entities which exist in the external world. So if Plantinga's ‘obvious fact’ is the first, then we may accept it as an evident fact but this fact never could be in conflict with the claim that Divine properties are identical in respect to their external existence. This consistency may become more obvious when we notice that in many cases (including ordinary as well as philosophical discourse) multiple concepts can easily be applied to one single object. However, if Plantinga means by the ‘obvious fact’ the external multiplicity, then his alleged fact seems to beg the question since someone who (like Aquinas) advocates Divine simplicity in the above sense actually believes that all Divine attributes are identical in respect to their external existence.

Plantinga's second objection prima facia looks more efficient. He writes:

One way for formulating this objection may be as follows:

1. 1. If God is identical with each of his properties, then He will be a property.

2. 2. All properties are abstract objects.

3. 3. No abstract object is a person.

4. 4. If God is identical with each of His properties, then He won't be a person.

5. 5. God is a person because He has knowledge, awareness, power, love and life.

6. ∴ God is not identical with His properties.

Understood in this way, the core of this objection is that the idea of God's being identical with His properties is incompatible with the belief that God is a person. The first premise seems to be a straightforward implication of the concept of identity. The second and third premises must be considered as tenets of contemporary analytic philosophy. The fifth premise is based on a common doctrine of Abrahamic religions and their picture of God as a personal Deity. I do not mean by ‘person’ here, to be sure, what is usually meant in the Christian doctrine of trinity. Instead, I mean the broader sense according to which (roughly speaking) an existent is a person if it has knowledge and power, does free actions and has specific relations with other persons. It seems that this broad sense of God's personhood is what the followers of all Abrahamic religions, including Muslims, Christians and Jews, can agree about.

One strategy to deal with Plantinga's objection is to move within its analytic framework and accept both of the second and third premises. This is adopted by some philosophers such as William Maan in his paper ‘Divine Simplicity’ (1982). Mann maintains that we may provide another reading of the old doctrine of Divine Simplicity according to which God is identical not with His properties but with His property instances and since a property instance is a concrete and not an abstract entity, the Doctrine of Divine Simplicity does not require God's being an abstract entity. He further introduces the somehow sophisticated notion of ‘rich property’ and argues that being a property instance and being a person are quite consistent since each person is in fact nothing but the property instance of his own rich property.

The second strategy which I am inclined to pursue here is to leave the analytic philosophy framework and consider Plantinga's objection within the medieval framework; the framework in which Aquinas’ view of Divine Simplicity is originally developed. I believe that the second strategy, if not more justifiable, is at least on a par with the first. As I will show below, from this perspective, Plantinga's objection would seem quite irrelevant.

It is important here to notice that the medieval ontology has been vastly influenced by Aristotelian logic and metaphysics. One of the prominent parts of Aristotle's philosophical legacy is his classification of categories according to which all beings can be classified into categories of substance, quality, quantity and relatives. And this view has been dominant in the philosophy of the middle ages for centuries. The contemporary analytical metaphysicians, however, rarely are inclined to accept the old-fashioned Aristotelian categories. Instead, we generally find them speak of properties, states of affairs, facts, events etc. as though these are alternative metaphysical categories. A short comparison between these two systems of categorization reveals essential differences and perhaps a few veiled similarities. In any case, according to the medieval metaphysics properties are not classified under a single distinct category. Rather ‘property’ in its broadest sense is applicable to all kinds of qualities as well as kinds of relatives. In this broad usage, we may say that any ordinary predicate (I said: ‘ordinary’ to prevent those non-ordinary paradoxical predicates like ‘is not a property of itself’) expresses a property so that for example, necessity, contingency, actuality and potentiality would seen as properties of a necessary, contingent, actual or potential existent. It may be that in the medieval metaphysics the ontological status of property as such could be not as obvious as we expect. But the certain point here is that, bearing this broad sense of ‘property’ in mind, a medieval thinker cannot simply accept the second premise of the above argument and contend that all properties are abstract objects. So we can be sure that when in a context of medieval metaphysics someone like Aquinas speaks of God's identity with His property he never means by ‘property’ the same of what is meant by a twentieth century philosopher who is thinking in an analytic atmosphere. In order to show this difference in a more clear way and prevent any equivocation fallacy, we may prefer ‘attribute’ instead of ‘property’; a medieval thinker considers knowledge, power etc. as God's attributes and not His properties.

The summary of my reply to Plantinga's second objection then could be that it is not compelling for a medieval philosopher because of the two radically different ideas of what a property is like. A medieval philosopher never sees a property as an abstract object and thus God's being identical with his properties does not imply His being an abstract object and not person. So, according to the medieval principle of Divine Simplicity, God could be still a person.