Ontological argument

An ontological argument for the existence of God attempts the method of a priori proof, which uses intuition and reason alone.^[1] In the context of the Abrahamic religions, ontological arguments were first proposed by the medieval philosophers Avicenna (in The Book of Healing)^[2][3] and, more famously, Anselm of Canterbury (in his Proslogion). Important variations were developed by later philosophers like Shahab al-Din Suhrawardi, René Descartes, Gottfried Leibniz, Norman Malcolm, Charles Hartshorne, and Alvin Plantinga. A modal-logic version of the argument was devised by the mathematician Kurt Gödel.

The ontological argument has been a controversial topic in philosophy. Many philosophers, including Gaunilo of Marmoutiers, David Hume, Immanuel Kant, and Gottlob Frege, have openly criticized it. Among Muslim philosophers al-Ghazali, Averroes and Mulla Sadra criticised Avicenna's argument in varied ways. Mulla Sadra put forward a substitute argument.

The argument examines the concept of God and argues that if we can conceive of God he must exist. The argument is often criticised as committing a bare assertion fallacy, as it offers no supportive premise other than qualities inherent to the unproven statement. This is also called a circular argument, because the premise relies on the conclusion, which in turn relies on the premise.

The differences among the argument's principal versions arise mainly from using different concepts of God as the starting point. Anselm, for example, starts with the notion of God as a being than which no greater can be conceived, while Descartes starts with the notion of God as being maximally perfect, or having all perfections.

Avicenna's argument

See also: Avicennism

Avicenna the great Muslim scientist and philosopher was the first person to come up with the ontological argument

The first recorded ontological argument for the existence of God was proposed by Avicenna (966-1037) in the Metaphysics section of The Book of Healing^[2][3] which is known as the contingency and necessity argument (Imakan wa Wujub).

Avicenna initiated a full-fledged inquiry into the question of being, in which he distinguished between essence (Mahiat) and existence (Wujud). He argued that the fact of existence can not be inferred from or accounted for by the essence of existing things and that form and matter by themselves cannot interact and originate the movement of the universe or the progressive actualization of existing things. Existence must, therefore, be due to an agent-cause that necessitates, imparts, gives, or adds existence to an essence. To do so, the cause must be an existing thing and coexist with its effect. ^[4]

According to Avicenna, the universe consists of a chain of actual beings, each giving existence to the one below it and responsible for the existence of the rest of the chain below. Because he deems an actual infinite impossible, the chain as a whole must terminate in a being that is wholly simple and one, whose essence is its very existence and therefore is self-sufficient and not in need of something else to give it existence. Because its existence is not contingent on or necessitated by something else, but necessary and eternal in itself, it satisfies the condition of being the necessitating cause of the entire chain that constitutes the eternal world of contingent existing things.^[4] Thus, Avicenna's ontological system rests on the conception of God, that is the First Cause, as the Wajib al-Wujud (necessary existent). There is a gradual multiplication of beings through a timeless emanation from God as a result of his self-knowledge.^[5][6] This was the first attempt at using the method of a priori proof, which utilizes intuition and reason alone. Avicenna's proof of God's existence is unique in that it can be classified as both a cosmological argument and an ontological argument. "It is ontological insofar as 'necessary existence' in intellect is the first basis for arguing for a Necessary Existent". The proof is also "cosmological insofar as most of it is taken up with arguing that contingent existents cannot stand alone and must end up in a Necessary Existent."^[7]

Anselm's argument

Anselm of Canterbury was one of the first to attempt an ontological argument for God's existence.

The ontological argument was proposed by Anselm of Canterbury (1033–1109) in the second chapter of his Proslogion.^[8] Although he did not propose an ontological system, he was very much concerned with the nature of being. He distinguished necessary beings (those which must exist) from contingent beings (those which may exist but whose existence is not necessary).

Anselm presented the ontological argument as part of a prayer directed at God. He began with a definition of God, or a necessary assumption about the nature of God, or perhaps both:

"Now we believe that [the Lord] is something than which nothing greater can be conceived."

He then asks if God exists.

"Then is there no such nature, since the fool has said in his heart: God is not?"

To answer this, he tries first to show that God exists "in the understanding":

"But certainly this same fool, when he hears this very thing that I am saying — something than which nothing greater can be imagined — understands what he hears; and what he understands is in his understanding, even if he does not understand that it is. For it is one thing for a thing to be in the understanding, and another to understand that a thing is."

Anselm goes on to justify his assumption, using the analogy of a painter:

"For, when a painter imagines beforehand what he is going to make, he has in his understanding what he has not yet made but he does not yet understand that it is. But when he has already painted it, he both has in his understanding what he has already painted and understands that it is.

"Therefore, even the fool is bound to agree that there is at least in the understanding something than which nothing greater can be imagined, because, when he hears this, he understands it, and whatever is understood is in the understanding."

Now Anselm introduces another assumption, which some philosophers have argued introduces a new version of the argument:

"And certainly that than which a greater cannot be imagined cannot be in the understanding alone. For if it is at least in the understanding alone, it can be imagined to be in reality too, which is greater."

"Therefore, if that than which a greater cannot be imagined is in the understanding alone, that very thing than which a greater cannot be imagined is something than which a greater can be imagined. But certainly this cannot be."

Anselm has thus found the contradiction from which he draws his conclusion:

"There exists, therefore, beyond doubt, something than which a greater cannot be imagined, both in the understanding and in reality."

A modern description of the argument

Anselm's Argument may be summarized thus:

1. God is, by definition, a being greater than anything that can be imagined and is the cause of all things, but is not bound causally by anything (otherwise God would be ontologically dependent on something else which would in turn undermine "its" greatness).
2. Existence both in reality and in imagination is greater than existence solely in one's imagination.
3. Therefore, God must exist in reality: if God did not, God would not be a being greater than anything which can be imagined.

This is a shorter modern version of the argument. Anselm framed a reductio ad absurdum, wherein he tried to show that the assumption that God does not exist leads to a logical contradiction. The following steps follow more closely Anselm's line of reasoning:

1. God is that entity than which nothing can be greater.
2. The concept of God exists in human understanding.
3. God exists in one's mind but not in reality.
4. The concept of God's existence is understood in one's mind.
5. If God existed in reality, it would be a greater thing than God's existence in the mind.
6. Therefore, God in reality must exist.

Anselm's second argument

Anselm in his Proslogion 3 made another a priori argument for God, this time based on the idea of necessary existence. He claimed that, if God is that than which no greater can be conceived, it is better to be necessary than contingent; therefore, God must be necessary. To sum up:

1. God is that entity than which nothing greater can be conceived.
2. It is greater to be necessary than not.
3. God must be necessary.
4. God necessarily exists.

Suhrawardi's argument

Shahab al-Din Suhrawardi(1155-1191) uses apagogical argument to show it is impossible that all of the existences are contingent beings. Due to the fact that this hypothesis means that the Set of all the things should be contingent. Then this contingent set needs a cause and that cause shouldn't be contingent beings or a member of that set. Because a member of the set can not be the cause of the set which itself is one of its members.^[9]

Descartes' ontological arguments

French thinker René Descartes composed several arguments that could be termed ontological.

René Descartes (1596–1650) composed a number of ontological arguments which differed from Anselm's formulation in important ways. Generally speaking, it is less a formal argument than a natural intuition.

Descartes wrote in the Fifth Meditation,^[10]

But if the mere fact that I can produce from my thought the idea of something that entails everything which I clearly and distinctly perceive to belong to that thing really does belong to it, is not this a possible basis for another argument to prove the existence of God? Certainly, the idea of God, or a supremely perfect being, is one that I find within me just as surely as the idea of any shape or number. And my understanding that it belongs to his nature that he always exists is no less clear and distinct than is the case when I prove of any shape or number that some property belongs to its nature (AT 7:65; CSM 2:45).

The intuition above can be formally described as follows:

1. Whatever I clearly and distinctly perceive to be contained in the idea of something, is true of that thing.
2. I clearly and distinctly perceive that necessary existence is contained in the idea of God.
3. Therefore, God exists.

In another, less formal statement of his argument, he draws an analogy between belief in the existence of God and the geometric demonstration:

Whatever method of proof I use, I am always brought back to the fact that it is only what I clearly and distinctly perceive that completely convinces me. Some of the things I clearly and distinctly perceive are obvious to everyone, while others are discovered only by those who look more closely and investigate more carefully; but once they have been discovered, the latter are judged to be just as certain as the former. In the case of a right-angled triangle, for example, the fact that the square on the hypotenuse is equal to the square on the other two sides is not so readily apparent as the fact that the hypotenuse subtends the largest angle; but once one has seen it, one believes it just as strongly. But as regards God, if I were not overwhelmed by philosophical prejudices, and if the images of things perceived by the senses did not besiege my thought on every side, I would certainly acknowledge him sooner and more easily than anything else. For what is more manifest than the fact that the supreme being exists, or that God, to whose essence alone existence belongs, exists? (AT 7:68–69; CSM 2:47)

In Meditations 8-10, Descartes offers a version of the ontological argument very similar to Anselm's which employs the same reductio method. The perfection of God logically requires existence, Descartes says, in the way a mountain logically implies a valley. And while the logical relationship between a mountain and a valley (or a triangle and the sum of its sides) does not imply real existence of those things, on the other hand: "because I cannot conceive God unless as existing, it follows that existence is inseparable from him, and therefore that he really exists: not that this is brought about by my thought, or that it imposes any necessity on things, but, on the contrary, the necessity which lies in the thing itself, that is, the necessity of the existence of God, determines me to think in this way: for it is not in my power to conceive a God without existence, that is, a being supremely perfect, and yet devoid of an absolute perfection, as I am free to imagine a horse with or without wings." (Descartes, Meditation 10)

Criticisms and objections

The ontological argument received much criticism and was rejected by St Thomas Aquinas,^[11] and therefore by some Catholic theologians.^[12] It has also received its share of criticism from non-Christians: Bertrand Russell noted of the argument that "it is easier to feel convinced that it must be fallacious than to find out precisely where the fallacy lies."^[13] The first objections were in the form of parodies, such as Gaunilo's Island, but some believe Immanuel Kant finally to have settled the matter with his famous rejection of existence as a property.^[14] Others believe that existence is indeed a property and that, if the proof is fallacious, the fallacy must lie elsewhere.

Among Muslims, al-Ghazali (1058-1111), Averroes (1126 – 1198), Mulla Sadra (1571–1640) and some others have criticized Avicenna's argument from different viewpoints.^[15]

Criticism on the basis of "Existence Precedes Essence"

Avicenna's argument is based on essence precedes existence. In his view existence is secondary to essence or quiddity, because a human can think about something and it need not exist. Everything that exists only comes into existence because it's brought from potential to actual existence by something else, except God, who is the only Necessary Existent. Averroes rejected Avicenna's ontological distinction between existence and essence. He argued that in an eternal universe anything that could exist would and indeed must exist, and existence of a thing is not just a property added to it.^[16][17] Mulla Sadra argued that reality is existence, differentiated in a variety of ways, and these different ways look to us like essences. What first affects us are things that exist and we forms ideas of essences afterwards, so existence precedes essence. This position is referred to as primacy of existence (Arabic: Isalat al-Wujud). ^[18][19]

General objection

David Hume did not believe an ontological argument was possible.

David Hume claimed that nothing could ever be proven to exist through an a priori, rational argument by arguing as follows:^[20]

1. The only way to prove something a priori is if its opposite implies a contradiction.
2. If something implies a contradiction, then it is inconceivable.
3. Everything can be conceived not to exist.
4. Nothing can be proven to exist a priori, including God.

Gaunilo's island

One of the earliest recorded objections to Anselm's argument was raised by one of Anselm's contemporaries, Gaunilo of Marmoutiers, who invited his readers to conceive of the greatest, or most perfect, island. As a matter of fact, it is likely that no such island actually exists. However, his argument would then say that we are not thinking of the greatest conceivable island, because the greatest conceivable island would exist, as well as having all those other desirable properties. Note that this is merely a direct application of Anselm's own premise that existence is a perfection (point 5 in the previous section). Since we can conceive of this greatest or most perfect conceivable island, it must exist. While this argument seems absurd, Gaunilo claims that it is no more so than Anselm's.

Such objections are known as "Overload Objections"; they do not claim to show where or how the ontological argument goes wrong; they simply argue that, if it is sound, so are many other arguments of the same logical form that we do not want to accept, arguments that would overload the world with an indefinitely large number of necessarily-existing perfect islands, perfect lizards, perfect pencils and the like.^[21]

There is a possible answer to this objection, put forward by the Roman Catholic philosopher Paul J. Glenn (who himself disagreed with the proof on other grounds) in his An Introduction to Philosophy. It is that Anselm's argument is only applicable to a being than which nothing greater can be conceived. Therefore, the island analogy is not appropriate, as it has only limited application (islands). The supreme being is not merely a platonic form, but a unique God who necessarily exists because his greatness is limitless. Islands are by definition limited; they need not have every greatness. God, to be God, must have. And so this proof could only apply to the greatest being possible.

Necessary nonexistence

Another rationale is attributed to Melbourne philosopher Douglas Gasking (1911–1994),^[22] one component of his proof of the nonexistence of God:

1. The creation of the world is the most marvelous achievement imaginable.
2. The merit of an achievement is the product of (a) its intrinsic quality, and (b) the ability of its creator.
3. The greater the disability (or handicap) of the creator, the more impressive the achievement.
4. The most formidable handicap for a creator would be non-existence.
5. Therefore if we suppose that the universe is the product of an existent creator we can conceive a greater being — namely, one who created everything while not existing.
6. Therefore, God does not exist.

The third premise might seem odd; the intuition is that we are generally more impressed by, for example, a four-year-old child composing a marvelous symphony than the same composition of a professional. In fact, Graham Oppy, a scholar on the ontological argument, who isn't particularly impressed with this parody, does not object to (3). Writing in the Stanford Encyclopedia of Philosophy, he is mainly concerned with the first premise, asking "what reason is there to believe that the creation of the world is 'the most marvelous achievement imaginable.' Gasking was apparently thinking of the "world" or "universe" as the same as "everything."

If one is willing to accept the first premise, one has no choice but to accept the fourth premise. Thus, the philosophical point of this parody is to highlight problems when existence is taken as property: "whereas Anselm illicitly supposed that existence is a perfection, [Gasking] is illicitly invoking the inverse principle that non-existence is a perfection."^[22]

Kant: existence is not a predicate

Immanuel Kant put forward a key, and influential, refutation of the ontological argument in the Critique of Pure Reason (first edition, pp. 592-603; second edition, pp. 620-631).^[23] It is explicitly directed primarily against Descartes but also against Leibniz. His criticism was anticipated in Pierre Gassendi's Objections to Descartes' Meditations. Kant's refutation consists of several separate but inter-related arguments. They are shaped by his central distinction between analytic and synthetic judgments. In an analytic judgment, the predicate expresses something that is already contained within a concept and is therefore a tautology; in a synthetic judgment, the predicate links the concept to something outside it that is not already logically implied by it. New knowledge consists of synthetic judgments.

Kant first argues that it is not at all clear that the idea of an absolutely necessary being even means anything at all, i.e. "whether I am still thinking anything in the concept of the unconditionally necessary, or perhaps rather nothing at all." ^[23]

Second, Kant argues that if we include existence in the definition of something, then asserting that it exists is a tautology. If we say that existence is part of the definition of God, in other words an analytic judgment, then we are simply repeating ourselves in asserting that God exists. We are not making a synthetic judgment that would add new information about the real existence of God to the purely conceptual definition of God.

Third, Kant argues that "'being' is obviously not a real predicate" ^[23] and cannot be part of the concept of something. That is, to say that something is or exists is not to say something about a concept, but rather indicates that there is an object that corresponds to the concept, and "the object, as it actually exists, is not analytically contained in my concept, but is added to my concept". For objects of the senses, to say that something exists means not that it has an additional property that is part of its concept but rather that it is to be found outside of thought and that we have an empirical perception of it in space and time. A really existing thing does not have any properties that could be predicated of it that differentiate it from the concept of that thing. What differentiates it is that we actually experience it: for example, it has shape, a specifiable location, and duration. To give an example of Kant's point: the reason we say that horses exist and unicorns do not is not that the concept of horse has the property of existence and the concept of unicorn does not, or that the concept of horse has more of that property than the concept of unicorn. There is no difference between the two concepts in this regard. And there is no difference between the concept of a horse and the concept of a really existing horse: the concepts are identical. The reason we say that horses exist is simply that we have spatio-temporal experience of them: there are objects corresponding to the concept. So any demonstration of the existence of anything, including God, that relies on predicating a property (in this case existence) of that thing is fallacious.

Thus, in accordance with the second and third arguments, the statement "God is omnipotent" is an analytic judgment that articulates what is already contained in and implied by the concept of God, i.e. a particular property of God. The statement "God exists" is a synthetic judgment of existence that does not assert something contained in or implied by the concept of God and would require knowledge of God as an object of that concept. What the ontological argument does is attempt to import into the concept of God, as though it were a property, the synthetic assertion of the existence of God, thereby illegitimately and tautologously defining God as existing. In other words, it "begs the question" by assuming what it purports to prove.

But, fourth, Kant argues that the concept of God is in any case not the concept of one particular object of sense among others but rather an "object of pure thought", of something that by definition exists outside the field of experience and of nature. With regard to unicorns, we can specify how we could determine that unicorns exist, i.e. what spatio-temporal experience of them would look like. With regard to the concept of God, there is no way for us to know it as existing in the only legitimate and meaningful way we know other objects as existing. And we cannot even determine "the possibility of any existence beyond that which is known in and through experience" ^[23].

The typical response to this objection to the ontological argument is this: "While 'existence' per se cannot be a predicate, 'necessary existence' (like 'contingent existence') can be a predicate." Some things are contingently so, and some things are necessarily so. God, it is said, is a necessary being de re. See Plantinga's ontological argument below for a discussion of "necessary existence."

Revisionists

Obviously Anselm thought this argument was valid and persuasive, and it still has occasional defenders, but many contemporary philosophers believe that the ontological argument, as Anselm articulated it, does not stand up to strict logical scrutiny.^[1] Others, like Gottfried Leibniz, Norman Malcolm, Charles Hartshorne, Kurt Gödel and Alvin Plantinga, have reformulated the argument in an attempt to revive it.

Among Muslim philosophers Mulla Sadra (c. 1571–1640) has criticized Avicenna's argument and discussed that it's not a priori argument. He also rejects that argument on the basis of Existence precedes essence. Then put forward new argument.^[19]

Mulla Sadra's ontological arguments

See also: Transcendent theosophy

Mulla Sadra (c. 1571–1640) put forward a new argument which is known as Argument of the Righteous (Arabic: Al-Burhan al-Siddiqin‎). This is an argument to prove the existence of God through the reality of existence, and to reach belief in God's pre-eternal necessity. In this argument, a thing is demonstrated through itself, and a path is identical with the goal. In other arguments, the truth is attained from other than itself, for example from the possible to the necessary, from the originated to the eternal origin, or from motion to the unmoved mover. But in the argument of the righteous, there is no middle term other than the truth.^[24]

Mulla Sadra describes this argument in Asfar as follows:^[25]

Existence is a single, objective and simple reality, and there is no difference between its parts, unless in terms of perfection and imperfection, strength and weakness… And the culmination of its perfection, where there is nothing more perfect, is its independence from any other thing. Nothing more perfect should be conceivable, as every imperfect thing belongs to another thing and needs to become perfect. And, as it has already been explicated, perfection is prior to imperfection, actuality to potency, and existence to non-existence. Also, it has been explained that the perfection of a thing is the thing itself, and not a thing in addition to it. Thus, either existence is independent of others, or it is in need of others. The former is the Necessary, which is pure existence. Nothing is more perfect than Him. And in Him there is no room for non-existence or imperfection. The latter is other than Him, and is regarded as His acts and effects, and for other than Him there is no subsistence, unless through Him. For there is no imperfection in the reality of existence, and imperfection is added to existence only because of the quality of being caused, as it is impossible for an effect to be identical with its cause in terms of existence. Therefore, if existence is not created through the creation of a creator, who has brought it into being and realized it, it cannot be imagined, and there is a sort of deficiency in it. Because, as you know, the reality of existence is simple, and for it there is no limit and determination, except pure acquisition and actuality. Otherwise, there should be combinations in it, or it has a quiddity other than its being. Also, as has been said, if existence is caused (the effect), it is essentially created through a simple creation, and its essence is in need of a creator and depends on its creator for its essence and substance. Thus it is proved and explained that existence is either perfect in terms of reality, necessity and essence, or essentially in need of a reality on which its substance depends. And in either case it is proved and explained that the existence of the Necessary Being is essentially needless of a cause…and this is what we sought to prove. To explain the eternal necessity, which is the same as the essential philosophical necessity, and to explain its difference from that of the essential logical necessity, we should refer to logic. It should be said that in logic when it is maintained that in a proposition such as the triangle has three sides, the predicate, i.e. 'having three sides', is essentially necessary for the subject, i.e. the triangle. This means that it is necessary for a triangle to have three sides, and this necessity is not confined to a particular time, condition, or aspect. That is, it is not so that only at a particular time it is necessary for a triangle to have three sides, for having three sides is inherent in the essence of the triangle. From a philosophical point of view, however, there is a condition for this necessity, which is the subsistence of the triangle. Only if the triangle remains as a triangle will it be necessary for it to have three sides. Now if we assume a necessity that does not even have this condition of the subsistence of the subject, and in which the attribution of the subject to the predicate is absolute, it will then be called the essential philosophical necessity, which means that a thing is not indebted to an external cause for its being in a necessary mode. This means that it is an independent and subsistent thing. This necessity should be eternal and pre-eternal. That is why it is also called the eternal necessity.^[24]

Plantinga's modal form and contemporary discussion

Alvin Plantinga has given another descriptive, initial version of the argument, one where the conclusion follows from the premises, assuming axiom S5 of modal logic. A version of his argument is as follows^[26]:

1. It is proposed that a being has maximal excellence in a given possible world W if and only if it is omnipotent, omniscient and wholly good in W; and
2. It is proposed that a being has maximal greatness if it has maximal excellence in every possible world.
3. Maximal greatness is possibly exemplified. That is, it is possible that there be a being that has maximal greatness. (Premise)
4. Therefore, possibly it is necessarily true that an omniscient, omnipotent and perfectly good being exists.
5. Therefore, it is necessarily true that an omniscient, omnipotent and perfectly good being exists. (By S5)
6. Therefore, an omniscient, omnipotent and perfectly good being exists.

This argument has two controversial premises: The axiom S5 and the "possibility premise" that a maximally great being is possible. The more controversial of these two is the "possibility premise" since S5 is widely (though not universally) accepted. One objection by Richard M. Gale, professor of philosophy at University of Pittsburgh, is that the "possibility premise" begs the question, because one only has the epistemic right to accept it if one understands the nested modal operators, and if one understands them then one understands that "possibly necessarily" is basically the same as "necessarily".^[27] Plantinga replies to this objection as follows: "Once you see how the argument works, you may think that asserting or believing the premise is tantamount to asserting or believing the conclusion; the canny atheist will say that he does not believe it is possible that there be a maximally great being. But would not a similar criticism hold of any valid argument? Take any valid argument: once you see how it works, you may think that asserting or believing the premise is tantamount to asserting or believing the conclusion." To deny premise (3) amounts to asserting that it is logically impossible that there is a being that exemplifies maximal greatness — thus the argument appears to demonstrate that either the existence of God is logically impossible or it is logically necessary.^[28]

There are, nonetheless, other approaches to the possibility premise. Leibniz thought that the possibility premise followed from the claim that "positive qualities" could not logically conflict with one another, and hence the notion of a being that had all the positive qualities had to be coherent. Gödel's ontological proof uses similar ideas.

A very different approach has recently been attempted by Alexander R. Pruss of Georgetown University.^[29] He starts with the 8th–9th century AD Indian philosopher Samkara's dictum that if something is impossible, then we cannot have a perception (even a non-veridical one) that it is the case. Contraposing, it follows that if we have a perception that p, then even though it might not be the case that p, it is at least the case that possibly p. If mystics in fact perceive the existence of a maximally great being, it follows that the existence of a maximally great being is at least possible. And that is all that is needed to get the modal ontological argument off the ground. One difficulty in this argument is that one might misinterpret the content of one's experience, and hence the mystic might be incorrect even in a cautious description of an experience as an experience "as of a maximally great being." Another problem would be if one could have an experience as of a universe that is uncreated, eternal and godless (i.e., devoid of a maximally great being), which, if experienced, must be possible, therefore breaking the necessity of said maximally great being.

Interestingly, Plantinga himself does not think the modal ontological argument is always a good proof of the existence of God. It depends on what his interlocutor thinks of the possibility premise. Nonetheless, Plantinga has suggested that because we do not have any evidence against the possibility premise, it might be reasonable to suppose it has probability 1/2. It follows from this that the existence of God can at the outset be held to have probability 1/2, though further evidence may increase or decrease this. Even though the possibility God does not exist is just as likely by this reasoning, Plantinga's point is to establish that even if one can't prove the existence of God, the argument is still victorious in the sense of justifying that belief in God is at least rational.

Notes

Bibliography

• Hartshorne, Charles, The Logic of Perfection (LaSalle, IL: Open Court, 1962)
• Jori, Alberto, 'Die Paradoxien des menschlichen Selbstbewusstseins und die notwendige Existenz Gottes — Zu 'Cogitatio' und 'Intellectus' im Streit zwischen Anselm und Gaunilo', in: C. Viola and J. Kormos (ed.), Rationality from Saint Augustine to Saint Anselm. Proceedings of the International Anselm Conference — Piliscsaba (Hungary) 20–23 June 2002 (Piliscsaba 2005), pp. 197–210.
• Leaman, Oliver; Peter S. Groff (2007). Islamic Philosophy A-Z. Edinburgh University Press. ISBN 0748620893. 
• Gracia, Jorge J. E.; Gregory M. Reichberg and Bernard N. Schumacher (2003). The Classics of Western Philosophy: A Reader's Guide. Blackwell Publishing. ISBN 0631236112. 
• Malcolm, Norman, "Anselm's Ontological Arguments" Philosophical Review, vol. 69, no. 1 (1960), 41–62

{reprinted in: "The Existence of God (Problems of Philosophy)" edited John Hick published Macmillan 1964 ISBN 0020854501 and also in : Knowledge and Certainty: Essays and Lectures by Norman Malcolm published Cornell University Press (Dec 1975) ISBN 0801491541.}

• Plantinga, Alvin, The Ontological Argument from St. Anselm to Contemporary Philosophers (Garden City, NY: Doubleday, 1965)
• Plantinga, Alvin. God, Freedom and Evil. (Grand Rapids, Michigan: Eerdmans, 1977) pp.85–112

See also

• Overviews: Arguments for the existence of God, Arguments against the existence of God
• Other major attempted proofs: Cosmological argument, Teleological argument, Argument from morality
• Gödel's ontological proof for the existence of God
• Pascal's Wager

External links

• Ontological Arguments — from the Stanford Encyclopedia of Philosophy
• Descartes' Ontological Argument — from the Stanford Encyclopedia of Philosophy
• Kenneth Einar Himma, The Ontological Argument — from the Internet Encyclopedia of Philosophy
• History of the ontological argument, with an annotated bibliography
• Medieval Sourcebook: Gaunilo: In Behalf of the Fool, and Anselm's Reply
• Medieval Sourcebook: Philosophers' Criticisms of Anselm's Ontological Argument for the Being of God
• Paul E. Oppenheimer & Edward N. Zalta, "On the Logic of the Ontological Argument" from James Tomberlin ed., Philosophical Perspectives 5: The Philosophy of Religion (Atascadero: Ridgeview, 1991) pp. 509–529
• Gregory S. Neal, "Anselm's Ontological Argument For the Existence of God" from Grace Incarnate (1990)
• Cartoon example of the ontologial argument, from Mac Hall
• Mulla Sadra’s Argument of the Righteous and a Critical Study of Kant and Hume’s Views on the Proofs of God’s Existence by Hamid Reza Ayatullahi