You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
The Ontological Argument stands apart from the design and cosmological arguments because it is a priori and deductive: it appeals to no observation of the world but tries to show, from the concept of God alone, that God must exist — and, if it works, exists necessarily, so that the denial of God's existence is not merely false but incoherent. The name (coined later, from the Greek ontos, "being") signals its method: it reasons from what it is to be God to the conclusion that God is. For the AQA 7062 course the named focus is Anselm's argument in the Proslogion, together with the two classic criticisms the specification names: Gaunilo's "perfect island" reductio and Kant's objection that "existence is not a predicate." This lesson sets out Anselm's argument with precision, develops both criticisms, notes Descartes' and the modal versions as enrichment, and reaches a judgement about whether an a priori argument can ever establish that something exists.
Key term: A priori argument — an argument whose conclusion is established by reason alone, independently of sense experience. The ontological argument is the paradigm case.
Key term: Deductive argument — an argument in which, if the premises are true, the conclusion must be true. A sound ontological argument would make God's existence logically certain, not merely probable.
St Anselm of Canterbury (1033–1109) develops the argument in the Proslogion (1077–78) — a work written as a prayer, addressed throughout to God, in the spirit of fides quaerens intellectum, "faith seeking understanding." This context matters a great deal for how the argument is read. Anselm is not, on the face of it, trying to argue a sceptic into belief from the outside; he is a believer seeking to understand what he already accepts on faith, asking God to help him see that God exists. This has prompted an important interpretive debate. The Reformed theologian Karl Barth (1886–1968) argued, influentially, that the Proslogion is not a "proof" in the modern evidential sense at all, but a piece of theology from within faith — an unfolding of what it means to call God "that than which nothing greater can be conceived," not an attempt to compel the unbeliever. On this reading, to treat Anselm as offering a knock-down proof to atheists is to misread the genre. Others insist that, whatever Anselm's devotional setting, he plainly does present a logical argument — addressed to the "fool" who denies God — and that it must be assessed as such. For exam purposes you can note both readings: the argument can be evaluated as a piece of logic, but the question whether Anselm intended it as a stand-alone proof is genuinely contested, and the Barthian reading is a legitimate evaluative move.
Anselm begins from a definition he thinks even an unbeliever must accept: God is "that than which nothing greater can be conceived" (aliquid quo nihil maius cogitari possit). Note carefully that this is a definition of God by means of unsurpassable greatness, not a list of attributes. Anselm then quotes Psalm 14: "The fool has said in his heart, there is no God." His point is that even this fool, in denying God, must understand what he is denying — so the concept "that than which nothing greater can be conceived" exists at least in the understanding (in intellectu).
Proslogion 2 then argues:
The form is a reductio ad absurdum: assuming God exists only in the mind generates a contradiction, so the assumption must be rejected. Anselm's striking move is to treat existing in reality as a great-making property, so that a merely-imagined God would not be the greatest conceivable being at all.
Two features of this argument deserve careful attention, because they are where it is attacked. The first is the distinction between existing in the understanding (in intellectu) and existing in reality (in re). Anselm illustrates it with a painter: before he paints, the picture he plans exists in his understanding but not in reality; once painted, it exists in both. His claim is that the second mode of existence is greater — a thing that is real as well as conceived has something a merely-conceived thing lacks. The whole argument depends on this comparative claim that in re trumps in intellectu, and it is precisely this that Kant will challenge by denying that existence is the sort of property that can make a thing greater.
Key term: In intellectu / in re — existing "in the understanding" (as an idea grasped by the mind) versus "in reality" (as an actual object). Anselm argues that to exist in re as well as in intellectu is greater than to exist in intellectu alone.
The second feature is the role of the fool (Latin insipiens). Anselm's argument is structured so that even the atheist's own position is turned against him: the very act of denying God requires understanding the concept of God, which (Anselm claims) places God in the atheist's understanding — and once there, the reductio is supposed to drive the concept inexorably out into reality. The argument thus has the form of showing that the denial of God is self-undermining: to deny "that than which nothing greater can be conceived" is, on Anselm's analysis, to think of something that, if it existed only in thought, would not be that than which nothing greater can be conceived — so the denial cannot be coherently maintained. This is a bold and elegant strategy; the question for evaluation is whether it is a genuine demonstration or a sleight of hand that confuses a feature of our concept of God with a fact about reality.
Proslogion 3 advances a second, arguably stronger form, turning not on existence simpliciter but on the mode of existence:
This second form is significant because it claims that necessary existence, not mere existence, is the perfection in question — anticipating both Kant's response and the modern modal versions. On Anselm's view, then, God is not the sort of being that happens to exist; God is the one being whose very nature rules out non-existence.
| Proslogion 2 | Proslogion 3 | |
|---|---|---|
| Great-making property | Existence in reality | Necessary existence |
| Claim | A real God > a merely imagined God | A God that cannot-not-exist > one that could fail to exist |
| Conclusion | God exists in reality | God exists necessarily |
| Form | Reductio ad absurdum | Reductio ad absurdum |
Anselm's two forms have generated both later restatements (Descartes' essence-based version and the modern modal argument) and the two classic objections the specification names — Gaunilo's "perfect island" parody and Kant's denial that existence is a predicate. We take Gaunilo's objection first, then Descartes and the modal reformulation, then Kant's objection and a general assessment.
Anselm's earliest critic was a fellow monk, Gaunilo of Marmoutiers, who replied On Behalf of the Fool (Pro Insipiente). Gaunilo's strategy is a parody (a reductio of Anselm's own method): if Anselm's reasoning is valid, the same form of argument will conjure into existence things that plainly do not exist, which shows the form must be defective.
His example is the most excellent island — "the Lost Island," than which no greater island can be conceived. Run Anselm's logic: such an island exists at least in my understanding; an island that exists in reality is greater than one existing only in thought; therefore the most excellent conceivable island must exist in reality. But this is absurd — I cannot bring a perfect island into being merely by defining it as perfect. Since the argument-form yields a false conclusion here, Gaunilo concludes it cannot be trusted to yield a true one in the case of God: you cannot define something into existence.
The deep point of Gaunilo's objection is methodological, and it is worth stating precisely. He is not claiming that God and islands are on a par; he is claiming that Anselm's method — moving from "the greatest conceivable F" plus "real existence is greater than mere conception" to "the greatest conceivable F exists" — must be invalid, because applied to islands (or, in later versions, to a perfect being of any other kind) it generates conclusions everyone agrees are false. If a method reliably produces falsehoods, the method is broken, even where its conclusion happens to be one we accept. So even a theist should be uneasy: Gaunilo's challenge is that the form of reasoning is untrustworthy, and pointing out that God is special does not, by itself, show that the form is sound — it may only show that we want the conclusion in God's case.
Anselm's reply is that the parody fails because an island is the wrong kind of thing. An island is a contingent being: there is no intrinsic maximum to island-greatness (one can always conceive a slightly better island — one more palm tree), and nothing in the concept of an island includes necessary existence. The argument, Anselm insists, works only for "that than which nothing greater can be conceived" — a being whose definition uniquely involves necessary existence. Islands, pizzas and the rest have their non-existence built into their nature as contingent things; God alone does not. Whether this reply succeeds is a central evaluative question: the defender says God is relevantly unique; the critic says Anselm has simply stipulated that uniqueness to dodge the parody.
There is a second strand to Anselm's defence, drawn from his Reply to Gaunilo. Anselm distinguishes between merely having the words in one's understanding and genuinely conceiving the thing they name. Gaunilo had complained that he could not really form the idea of "that than which nothing greater can be conceived" — the words were in his mind, but no corresponding object. Anselm answers that, even so, the argument needs only that one understands the formula well enough to see that, whatever it refers to, it cannot consistently be thought not to exist; the logic operates on the definition, not on a mental picture. Critics press back that this makes the argument suspiciously verbal — it seems to extract a fact about reality from the mere meaning of a phrase. The dispute over what it is to "conceive" God recurs throughout the argument's history and is worth flagging: the believer says the concept of the greatest possible being is coherent and uniquely involves necessary existence; the sceptic says we do not have a clear enough grasp of "the greatest possible being" to know that it is even possible.
Key term: Reductio ad absurdum — refuting a claim (or a method) by showing that it leads to an absurd or contradictory conclusion. Both Anselm (against the fool) and Gaunilo (against Anselm) use this strategy.
The argument did not die with the Middle Ages; two later restatements are important enough to develop in their own right.
René Descartes (1596–1650), in Meditation V, recasts the argument around the idea of essence. God, Descartes says, is a "supremely perfect being." Now just as it belongs to the essence of a triangle that its three angles equal two right angles, and to the essence of a mountain that it is accompanied by a valley, so it belongs to the essence of a supremely perfect being that it exists — for existence is a perfection, and a supremely perfect being lacking a perfection would be a contradiction in terms. Descartes is careful to anticipate the obvious objection — that I cannot think a mountain into being merely because I cannot think a mountain without a valley. He replies that the cases differ: from the fact that I cannot think God without existence, it follows that existence is inseparable from God, and hence that God exists — whereas thinking a mountain-with-valley tells me only about the relation of two ideas, not that any mountain exists. Whether this reply works is exactly what Kant will deny. A further worry, pressed in Descartes' own time by Pierre Gassendi, is that Descartes simply assumes what is in dispute — that existence is a perfection or property that God's essence can "contain" — which is the very assumption Kant later denies; if existence is not a property, then it cannot belong to God's essence as three-sidedness belongs to a triangle's, and the parallel breaks down.
| Anselm (Proslogion 2) | Anselm (Proslogion 3) | Descartes | |
|---|---|---|---|
| Definition of God | That than which no greater can be conceived | (same) | A supremely perfect being |
| Great-making property used | Existence in reality | Necessary existence | Existence as a perfection |
| Analogy / device | Reductio | Reductio | Essence (triangle / mountain–valley) |
The most discussed modern form is the modal ontological argument of Norman Malcolm (1911–1990) and, in its best-known version, Alvin Plantinga (b. 1932), which revives Anselm's second form using the logic of possible worlds (a "possible world" being a complete way things could have been). Plantinga's argument can be set out as:
Subscribe to continue reading
Get full access to this lesson and all 10 lessons in this course.