Ontological argument for the existence of God

An ontological argument sets out to prove the existence of the God of the monotheistic religions from the nature of concepts alone. It is thus an a priori argument. The term "ontological argument" originates with Immanuel Kant (who rejected the argument form), though it can be traced, in various forms, back to the work of Aristotle.

The argument typically works via a reductio ad absurdum: it presents a certain concept (for example that of a maximally perfect being — a being that has every possible perfection), supposes that such a being does not exist, and then draws out a contradiction, thus proving that such a being exists. That being is then identified with God. In other words, the concept implies its own instantiation; if one grasps the concept of God, then one is committed to the existence of God. (A separate argument is needed to show that there can be only one instantiation of the concept — only one God.)

The best-known uses of the argument are to be found in the context of the Abrahamic religions, its earliest formulation being found in the Proslogion of the eleventh-century philosopher and theologian Anselm of Canterbury. It was rejected and argued against by the thirteenth-century philosopher and theologian Thomas Aquinas, and was for some time neglected, but the early modern period saw its revival. René Descartes presented what became probably the best-known form of the argument, but versions were devised by prominent philosophers such as Gottfried Leibniz and Baruch Spinoza. In the modern period, attempts have been made to devise up-dated versions of the argument, most notably by Norman Malcolm, Charles Hartshorne, and Alvin Plantinga.

Anselm's version was criticised by Aquinas and by Anselm's contemporary, Gaunilo. Descartes' version was criticised by many of his contemporaries, including Caterus and Pierre Gassendi, and later by such philosophers as as Kant, David Hume, and Gottlob Frege.

The differences between the different versions of the argument are generally a matter of the precise nature of the starting concept.

Mediæval versions

Anselm of Canterbury

Anselm of Canterbury (1033–1109) introduced the ontological argument to the Christian world in Chapter II of his Proslogion. The concept with which he starts is that of a being than which no greater can be conceived. He then refers to the "fool" who "hath said in his heart, there is no God" (Psalms xiv 1), and argues that the fool at least understands the concept of a being than which no greater can be conceived. Now he brings out the contradiction, for the fool must understand the being than which no greater can be conceived as existing only in his understanding — but then he could also conceive of that being as existing reality, and that would be a greater being than the one just in his understanding. How could there be a being greater than a being than which no greater can be conceived? Therefore, a being than which no greater can be conceived must exist both in the understanding and in reality.

In Chapter III of Proslogion, Aquinas goes on to argue that God – the being than which no greater can be conceived – necessarily exists (cannot be conceived not to exist), because a being that cannot be conceived not to exist is greater than one which can be conceived not to exist (a contingent being). Thus, he says, God exists "more truly than all other beings, and hence in a less degree".

In Chapter IV, Anselm asks how, if the denial of the existence of God is a contradiction, people do seem to deny it. He explains it by distinguishing between the mere reciting of words and the genuine holding of a concept. One might say (in speech or thought) "God doesn't exist" (just as one might say "a round square exists"), but one cannot conceive it. Although saying words to oneself might be called conceiving in a weak sense, the stronger sense of conceiving involves the understanding of what is conceived: "In the former sense, then, God can be conceived not to exist; but in the latter, not at all."

Gaunilo's criticisms

The first critic of Anselm's argument was Gaunilo, a monk at Marmoutier and Anselm's contemporary; little is known about him apart from his criticism of the ontological argument: In Behalf of the Fool.

Gaunilo offers two sorts of criticism (to which Anselm replied at length). He starts by examining the assumptions made by Anselm and the logical structure of his argument.

Gaunilo then goes on to offer his best-known criticism, which takes the form of what has become known as an "overload objection". That is, rather than trying to uncover a flaw in the logic of the argument, or challenging one of its premises, he offers an argument by analogy, designed to show that, if the ontological argument were sound, then so would be many other arguments of the same logical form, and this would mean that we were committed to overloading the universe with the existence of a potentially infinite number of things, few of which we should want to accept existed.

Gaunilo's analogy uses the notion of a lost island — an island than which no greater can be conceived. He argues that, given that we have the concept of such an island, and given that – on Anselm's assumptions – it is greater to exist in reality than in the understanding alone, then it would be contradictory to say that the lost island doesn't exist.

Bibliography

• Anselm of Canterbury (translated by S.N. Deane, introduction by Charles Hartshorne) Anselm's Basic Writings. LaSalle, Illinois: Open Court, 1962. (Chapter II–IV reprinted in Plantinga [1965])
• Anselm of Canterbury (translated by Jonathan Barnes) Anselm's Proslogium or Discourse on the Existence of God. David Banach's Web site.
• Charles Hartshorne The Logic of Perfection. LaSalle, Illinois: Open Court, 1962.
• Norman Malcolm "Anselm's Ontological Arguments". Philosophical Review 69:1 (1960), pp 41–62. Reprinted in his Knowledge and Certainty: Essays and Lectures by Norman Malcolm. Ithaca, New York: Cornell University Press, 1975. ISBN 0801491541 (also in Plantinga [1965]).
• Gregory S. Neal "Anselm's Ontological Argument for the Existence of God", from Grace Incarnate (1990)
• Alvin Plantinga The Ontological Argument from St Anselm to Contemporary Philosophers. Garden City, New York: Doubleday, 1965.
• Alvin Plantinga God, Freedom, and Evil. Grand Rapids, Michigan: Eerdmans, 1977.

External links

• Gaunilo: "In Behalf of the Fool", and Anselm's Reply — the Medieval Sourcebook
• Philosophers' Criticisms of Anselm's Ontological Argument for the Being of God — the Medieval Sourcebook