An ontological argument for the existence of God (or simply ontological argument) is any one of a category of arguments for the existence of God. Although the exact criteria that allow for the classification of any given argument as "ontological" are not widely agreed, a typical definition leaves as ontological those arguments that are based solely on a priori reasoning and include little if any reference to empirical observations of the world. Most attempt to prove God's existence using only the definition of God.
The first argument to be widely recognised as belonging to the category was that proposed by the eleventh-century monk Anselm of Canterbury. First, Anselm defined God as the greatest possible being we can conceive. He suggested that, if we can conceive of the greatest possible being, it must exist in reality. If it does not exist in reality, a greater being is possible—one which does exist. The seventeenth century French philosopher René Descartes also deployed a similar argument. Although Descartes published several variations of his argument, each centered on the idea that God's existence is immediately inferable from any "clear and distinct" idea of a supremely perfect being. In the early eighteenth century, Gottfried Leibniz slightly augmented Descartes' ideas in an attempt to prove that a "supremely perfect" being is a coherent concept. More recent ontological arguments have come from Kurt Gödel, who proposed a formal argument for God's existence, and Alvin Plantinga, who based his ontological argument on modal logic. Attempts have also been made to validate Anselm's proof using an automated theorem prover. Other arguments have also been categorised as ontological, including those made by Islamic philosopher Mulla Sadra.
Ontological proofs have long attracted crticism. Anselm's contemporary, Gaunilo of Marmoutiers, criticised the ontological argument using the analogy of a perfect island, suggesting that the ontological could be used to prove the existence of anything. Thomas Aquinas later rejected the argument on the basis that humans cannot know God's nature. David Hume took empirical objection to the argument, criticising its lack of evidential reasoning and rejected the idea that anything can exist necessarily. Immanuel Kant put forward an objection to the argument, based on what he saw as the false premise that existence is a predicate. He proposed that, as it adds nothing to the essence of a being, existence is not a predicate (or perfection) and thus a "supremely perfect" being can be conceived to not exist. Douglas Gasking presented a parody to the ontological argument, recorded and published by William Grey, using a version of the argument to prove God's existence, in an attempt to demonstrate the argument's flaws. Finally, philosophers including C. D. Broad have dismissed the coherence of a maximally great being, proposing that some attributes of greatness are incompatible with others, making a maximally great being incoherent.
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The traditional definition of an ontological argument was given by Immanuel Kant.[1] Kant contrasted the ontological argument (literally any argument "concerned with being"[2]) with cosmological and physio-theoretical arguments.[3] According to the Kantian view, ontological arguments are those which are founded on a priori reasoning.[1]
Writing for the Stanford Encyclopedia of Philosophy (SEP), Graham Oppy (who has elsewhere expressed the view that he "see[s] no urgent reason" to depart from the traditional definition[1]) defines ontological arguments as those beginning with "nothing but analytic, a priori and necessary premises" and concluding that God exists.[4] However, Oppy admits that these "traditional characteristics" of an ontological argument (analyticity, necessity, and a priority) are not all found in all ontological arguments,[4] and, in his 2007 work Ontological Arguments and Belief in God, suggests that a better definition of an ontological argument would be one whose considerations are "entirely internal to the theistic worldview".[1]
In the SEP article, Oppy subclassifies ontological arguments as being of a definitional, conceptual (or hyperintensional), modal, Meinongian, experiential, mereological, higher-order, or Hegelian nature.[4]
Although the ontological argument may have been implicit in the works of Greek philosophers such as Plato and the Neoplatonists,[5] the mainstream view is that the ontological argument was first clearly stated and developed by St Anselm.[4][6][7][8] Some scholars have argued that the Islamic philosopher Avicenna (Ibn Sina) developed a special kind of ontological argument before Anselm;[9][10] however, this position is doubted by a number of scholars.[11][12][13]
The ontological argument was first proposed by Anselm of Canterbury (1033–1109) in the second and third chapter of his Proslogion.[14] The argument Anselm puts forward is not, however, presented in order to prove God's existence. Rather, Proslogion is more a work of meditation, in which he documents how the idea of God had become self-evident to him.[15]
In Chapter 2 of the Proslogion, Anselm defines what we understand as God to be a "being than which no greater can be conceived".[4] Anselm suggests that we understand the concept of a "being than which no greater can be conceived" and what it brings causes to exist in the mind. The concept must exist either only in our mind or in our mind and in reality. If such a being exists only in our mind, then a greater being - that which exists in reality as well - can be conceived. Therefore, if we can conceive of a being that than which nothing greater can be conceived, then it must exist in reality. Therefore, a being that than which nothing greater could be conceived must exist in reality.[16]
In Chapter 3 of the Proslogion, Anselm suggests the notion of a being that cannot be conceived not to exist (similar to the notion of a necessary being). He argues if something can be conceived not to exist, then it is not that than which nothing greater can be conceived. Consequently, that than which nothing greater can be conceived cannot be conceived not to exist. This can be read either as a gloss on the argument in Chapter 2, as a new (and superior, according to Norman Malcolm)[17] version of the argument, or as the first of Anselm's derivations of divine attributes from the concept of the maximally great being, in this case the attribute of necessity.[16]
René Descartes (1596–1650) composed a number of ontological arguments, which differed from Anselm's formulation. Generally speaking, it is less a formal argument than a natural intuition.
Descartes wrote in the Fifth Meditation,
But, if the mere fact that I can produce from my thought the idea of something that entails everything that 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.—Descartes, (AT 7:65; CSM 2:45)[18]
Descartes argues that God's existence can be deduced from his nature, just as geometric ideas can be deduced from the nature of shapes - Descartes uses the deduction of the sizes of angles in a triangle as an example. Descartes suggests that the concept of God is that of a supremely perfect being, holding all perfections fully. He proposes that existence is a perfection: it would be better to exist than not to exist. Thus, if the notion of God did not include existence, it would not be supremely perfect, as it would be lacking a perfection. Consequently, the notion of a supremely perfect God who does not exist, Descartes argues, is unintelligible. Therefore, according to his nature, God must exist.[19]
Gottfried Leibniz saw a problem with Descartes' ontological argument: that Descartes had not asserted the coherence of a "supremely perfect" being. He proposed that, unless the coherence of a supremely perfect being could be demonstrated, the ontological argument fails. Leibniz saw perfection as impossible to analyse; therefore, it would be impossible to demonstrate that all perfections are incompatible. He reasoned that all perfections can exist together in a single entity, and that Descartes' argument is still valid.[4]
Mulla Sadra (c. 1571–1640) was an Islamic philosopher, influenced by Avicenna's philosophy. Sadra discussed Avicenna's arguments for the existence of God, claiming that is was not an a priori argument and rejecting the argument on the basis that existence precedes essence.[20]
Sadra put forward a new argument, known as Argument of the Righteous (Arabic: البرهان الصديقين — Al-Burhan al-Siddiqin). The argument attempts to prove the existence of God through the reality of existence, and to conclude with 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 somewhere 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.[21] His version of the ontological argument can be summarised as follows:[20]
Mulla Sadra describes this argument in Asfar as follows:[22]
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.
Mathematician Kurt Gödel provided a formal argument for God's existence. The arguments were constructed by Gödel but not published until long after his death. Gödel provides a logically valid argument based on modal logic; he uses the conception of properties, ultimately concluding with God's existence. His listed theorems follow from the axioms, so most criticisms focus on the axioms used or the assumptions made. Some philosophers have challenged Gödel's acceptance of the underlying modal logic while others have criticised Gödel's wide conception of properties.[23]
Alvin Plantinga has presented another version of the argument. The conclusion he provides logically follows from the premises, assuming axiom S5 of modal logic. This is the axiom that if it is possible something is true, then its possibility is necessary - it is possibly true in all worlds - and if something possibly necessary, then it is necessarily true - it is always true in all worlds.[24]
A version of his argument is as follows:[25]
This argument has two controversial premises: the axiom S5 and the "possibility premise" - that a maximally great being is possible. S5 is widely accepted, though not in the form taken here. Paul Almond criticised the argument due to the "incoherence, incorrectness and triviality" of axiom S5.[26]
The more controversial premise is the "possibility premise". Richard M. Gale, professor emeritus of philosophy at University of Pittsburgh, argues that the "possibility premise" begs the question, because one has the epistemic right to accept it only if one understands the nested modal operators, and if one understands them within the system S5 (without which the argument fails) then one understands that "possibly necessarily" is in essence the same as "necessarily".[27]
An approach to supporting the possibility premise in Plantinga's version of the argument has been attempted by Alexander R. Pruss, currently of Baylor University. He starts with the 8th–9th century AD Indian philosopher Sankara's dictum that if something is impossible, we cannot have a perception (even a non-veridical one) that it is the case. 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.[28]
In a paper published in the Australasian Journal of Philosophy, Paul Oppenheimer and Edward Zalta describe how they used an automated theorem prover called Prover9 to validate Anselm's ontological thesis. The Prover9 reasoning engine subsequently discovered a simpler formally valid (if not necessarily sound) ontological argument from a single non-logical premise.[29]
One of the earliest recorded objections to Anselm's argument was raised by one of Anselm's contemporaries, Gaunilo of Marmoutiers. He invites his reader to conceive an island "more excellent" than any other island. He suggests that, according to Anselm's proof, this island must necessarily exist, as an island that exists would be more excellent.[30] Gaunilo's criticism does not explicitly demonstrate a flaw in Anselm's argument; rather, it argues that, if sound, so are many other argument of the same logical form that cannot be accepted.[31]
Gaunilo offered a further criticism of Anselm's ontological argument. He suggested that the notion of God cannot, as Anselm asserted, be conceived. He argued that many theists would accept that God, by nature, cannot be fully comprehended. Therefore, if humans cannot fully conceive of God, the ontological argument cannot work.[32]
Anselm responded to Gaunilo's criticism by suggesting that argument applied only to concepts with necessary existence. He suggested that only a being with necessary existence can fulfill the remit of "that than which nothing greater can be conceived". Furthermore, a contingent object, such as an island, could always be improved and thus could never reach a state of complete perfection. For that reason, Anselm dismissed any argument which did not relate to a being with necessary existence.[30]
St. Thomas Aquinas, while proposing five proofs of God's existence in his Summa Theologica, objected to Anselm's argument. He suggested that people cannot know the nature of God and, therefore, cannot conceive of God in the way Anselm proposed.[33] The ontological argument would be meaningful only to someone who understands the essence of God completely. Aquinas reasoned that, as only God can completely know his essence, only he can use the argument.[34] Aquinas' rejection of the ontological argument caused some Catholic theologians to also reject the argument.[35]
Scottish philosopher and empiricist, David Hume, argued that nothing can be proven to exist using only a priori reasoning.[36] In his Dialogues Concerning Natural Religion, the character Cleanthes proposes this argument:
Hume also suggested that, as we have no abstract idea of existence (apart from as part of our ideas of other objects), we cannot claim that the idea of God implies his existence. He suggests that any conception of God we may have, we can conceive either of existing or of not existing. Existence is not a quality (or perfection), so the concept of a completely perfect being need not actually exist. Thus, he claims that it is not a contradiction to deny God's existence.[36] Although this criticism is directed against a cosmological argument, similar to that of Samuel Clarke in his first Boyle Lecture, it can be applied to ontological arguments as well.[38]
Immanuel Kant put forward a key refutation of the ontological argument in his Critique of Pure Reason (first edition, pp. 592–603; second edition, pp. 620–631).[39] It was primarily and explicitly directed at René Descartes, but also attacked the position of Gottfried Leibniz. Kant's refutation consists of several separate but interrelated arguments, 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, or claim, links the concept to something outside it that is not already logically implied by it. New knowledge consists of synthetic judgments.[40]
Kant first questions the intelligibility of the concept of a necessary being. He considers examples of necessary proposition, such as "a triangle has three angles", and rejects the transfer of this logic to the existence of God. First, he argues that such necessary propositions are necessarily true only if such a being exists: If a triangle exists, it must have three angles. The necessary proposition, he argues, does not make the existence of a triangle necessary. Thus, he argued that, if the proposition "X exists" is posited, it would follow that, if X exists, it exists necessarily; this does not mean that X does exist in reality.[41] Second, he argues that contradictions arise only when the subject and predicate are maintained and, therefore, a judgement of non-existence cannot be a contradiction, as it denies the predicate.[39]
Kant then proposes that the statement "God exists" must be either analytic or synthetic - the predicate must be either inside or outside of the subject, respectively. If the proposition is analytic, as the ontological argument takes it to be, then the statement would be true only because of the meaning given to the words. Kant argues that this is merely a tautology and cannot say anything about reality. However, if the statement is synthetic, the ontological argument does not work, as the existence of God is not contained within the definition of God (and, as such, evidence for God would need to be found).[42]
Kant goes on to argue that "'being' is obviously not a real predicate" [39] and cannot be part of the concept of something. He proposes that existence is not a predicate, or quality. This is because existence does not add to the essence of a being, indicating merely its occurrence in reality. He suggests that, if he takes the subject of God with all its predicate and then asserts that God exists, "I add no new predicate to the conception of God". He argues that the ontological argument works only if existence is a predicate; if this is not so, then it is conceivable for a completely perfect being to not exist, thus defeating the ontological argument.[16]
In addition, Kant argues that the concept of God is not of one a particular sense; rather, it is an "object of pure thought".[39] He presents the view that God exists outside the realm of experience and nature. Because we cannot experience God through experience, Kant argues that it is impossible to know how we would verify God's existence. This is in contrast to material concepts, which can be verified by means of the senses.[43]
Melbourne philosopher Douglas Gasking (1911–1994) developed his own version of the ontological argument to prove God's non-existence. The argument was not intended to be serious; rather, its purpose was to illustrate the problems Gasking saw.[44] The argument was published by William Grey at the University of Queensland.[45]
Gasking argument asserts that the creation of the world is the most marvellous achievement imaginable. The merit of such an achievement is the product of its quality and the creator's ability: the greater the disability of the creator, the more impressive the achievement. Non-existence, it is argued, would be the greatest handicap. Therefore, if the universe is the product of an existent creator, we could conceive of a greater being - one which does not exist. A non-existent creator is greater than one which exists, so God does not exist.[45]
Gasking proposes that the greatest disability would be non-existence as a response to Anselm's assumption that existence is a predicate and perfection. Gasking uses this logic to assume that non-existence must be a disability.[44]
Graham Oppy, a philosopher of religion, has criticised the argument in the Stanford Encyclopedia of Philosophy. He suggests that, though it may be accepted that it would be a greater achievement for a non-existent creator to create something than a creator who exists, there is no reason assume that a non-existent creator would be a greater being. He continues his criticism by arguing that there is no reason to view the creation of the world as "the most marvellous achievement imaginable". Finally, he suggests that it may be inconceivable for a non-existent being to create anything at all. Thus, Oppy views Gasking's criticism as a weak parody of the ontological argument.[4]
In his development of the ontological argument, Leibniz attempted to demonstrate the coherence of a supremely perfect being.[4] This problem has, however, been criticised. C. D. Broad suggested that, if there are two characteristics necessary for God's perfection that are incompatible with a third, the notion of a supremely perfect being becomes incoherent. The ontological argument assumes the definition of God purported by classical theism: that God is omnipotent, omniscient, and morally perfect. Kenneth Einar Himma has noted suggested that omniscience and omnipotence may be incompatible: if God is omnipotent, then he should be able to create a being with free will; if he is omniscient, then he should know exactly what such a being will do (thus rendering them without free will). This analysis would render the ontological argument incoherent, as the characteristics required of a maximally great being cannot coexist in one being, thus such a being could not exist.[46]
Bertrand Russell criticised the argument, asserting that "the argument does not, to a modern mind, seem very convincing, but it is easier to feel convinced that it must be fallacious than it is to find out precisely where the fallacy lies." He also drew a distinction between existence and essence, arguing that the essence of a person can be described and their existence still remain in question.[47] During his early Hegelian phase, Russell accepted the argument, once exclaiming: "Great God in Boots! — the ontological argument is sound!"[48] Richard Dawkins has also rejected the argument as "infantile" and “dialectical prestidigitation”.[49]
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