The Ontological Argument

The ontological argument is unique among arguments for God's existence. While cosmological arguments begin with observed features of the world and teleological arguments point to apparent design, the ontological argument begins with the very concept of God and attempts to demonstrate that such a being must exist. It is the most abstract and controversial of the classical arguments—dismissed by some as mere wordplay, defended by others as a profound insight into necessary existence. Understanding this argument, even if one remains uncertain about it, illuminates deep questions about the nature of existence and the concept of God.

The Argument's Distinctive Character

The ontological argument is an a priori argument—it proceeds from concepts and definitions rather than from empirical observations. While other arguments begin with facts about the world (the universe began, the universe is fine-tuned, morality exists), the ontological argument begins with an analysis of what we mean by "God."

This makes the argument both powerful and puzzling. If it succeeds, it establishes God's existence with the certainty of logical proof—no empirical discoveries could overturn it. But many find it suspicious: how can we prove existence from mere concepts? Don't we need to look at the world to know what exists?

The argument has attracted some of history's greatest minds—Anselm, Descartes, Leibniz, Gödel, Plantinga—and some of its sharpest critics—Gaunilo, Aquinas, Kant, Russell. This intellectual history should make us approach the argument with both interest and caution.

Anselm's Original Formulation

The ontological argument was first formulated by Anselm of Canterbury (1033-1109) in his work Proslogion. Anselm was not trying to convince atheists but to understand what he already believed. His argument emerged from prayerful meditation on God's nature.

The Argument

Anselm defines God as "that than which nothing greater can be conceived"—the greatest conceivable being (GCB). This isn't an arbitrary definition; it captures what theists mean by God: the supreme being, unsurpassable in every perfection.

Now, even the "fool" who says "there is no God" (Psalm 14:1) understands this concept. The idea of the greatest conceivable being exists in the understanding—in the mind—even of someone who denies that such a being exists in reality.

But here's the key move: which is greater—something that exists only in the mind, or something that exists both in the mind and in reality? Surely the latter. Real existence adds to greatness. A real hundred dollars is greater (more useful, more valuable) than a merely imaginary hundred dollars.

So suppose the greatest conceivable being exists only in the mind and not in reality. Then we could conceive of something greater—namely, that same being existing in reality as well. But this contradicts our definition: the GCB is that than which nothing greater can be conceived. If we can conceive of something greater, our original being wasn't the GCB after all.

Therefore, the greatest conceivable being must exist not only in the mind but in reality as well. God—the GCB—exists.

Gaunilo's Objection

Shortly after Anselm published his argument, a monk named Gaunilo raised an objection that still resonates today. If Anselm's reasoning works for God, Gaunilo suggested, it should work for other "greatest conceivable" things—like the greatest conceivable island. By parallel reasoning:

The greatest conceivable island exists in the understanding. If it existed only in the understanding, we could conceive of something greater (that island existing in reality). Therefore, the greatest conceivable island must exist in reality.

But this is absurd. We can't prove the existence of perfect islands by definition. Something must be wrong with the reasoning.

Anselm's Reply

Anselm responded that his argument applies uniquely to God because only God is the greatest conceivable being in an absolute sense. Islands, however great, are limited beings; there's no intrinsic maximum to island-greatness (more palm trees? better weather? the concept is open-ended). But God is unlimited—the concept of maximal greatness has determinate content when applied to a being with every perfection.

More fundamentally, Anselm's argument depends on necessary existence as a great-making property. A being that exists necessarily (cannot fail to exist) is greater than one that exists contingently (might not have existed). This property applies to God, who is conceived as necessarily existent, but not to islands, which are by nature contingent.

Kant's Critique

The most famous critique of the ontological argument comes from Immanuel Kant (1724-1804). Kant argued that the argument makes a fundamental error: it treats existence as a property or predicate that adds to a concept.

Existence Is Not a Predicate

When we say "God is omnipotent," we add the predicate "omnipotent" to our concept of God. But when we say "God exists," according to Kant, we don't add a predicate to the concept. Existence is not a property alongside omnipotence, omniscience, and so on. Rather, to say "God exists" is to say that the concept of God is instantiated—that there is something in reality corresponding to the concept.

Consider: a hundred real dollars and a hundred imaginary dollars have the same properties (same denomination, same purchasing power in principle). The real dollars don't have more properties than the imaginary ones; they just actually exist. Existence adds nothing to the concept.

If this is right, then Anselm's argument fails at step 3. Existence in reality is not "greater" than existence in the understanding, because existence isn't the kind of thing that can make something greater. It doesn't add to the concept.

Evaluating Kant's Critique

Kant's critique is powerful but not universally accepted. Some philosophers argue that while Kant may be right about first-order existence, the argument can be reformulated in terms of necessary existence. Necessary existence—existing in all possible worlds, being unable not to exist—does seem to be a great-making property. A being that exists necessarily is arguably greater than one that exists merely contingently.

This moves the debate to whether necessary existence is coherent and whether it can be known a priori. Contemporary modal versions of the ontological argument take up this challenge.

The Modal Ontological Argument

Alvin Plantinga has developed a contemporary version of the ontological argument using modal logic—the logic of possibility and necessity. This version avoids some objections to Anselm's formulation.

Key Concepts

Possible worlds are ways things could have been—complete descriptions of possible realities. The actual world is one possible world; others include worlds where dinosaurs never went extinct, where you chose differently this morning, or where different physical laws obtain.

A necessary truth is true in all possible worlds (like mathematical truths). A contingent truth is true in some possible worlds but not others (like "Trump was president"). A necessary being exists in all possible worlds; a contingent being exists in some but not all.

The Argument

Plantinga defines a maximally excellent being as one that has maximal greatness in every possible world—omnipotent, omniscient, and morally perfect in every possible world. Such a being would be necessarily existent (existing in all possible worlds).

The argument:

The crucial premise is the first: it is possible that a maximally great being exists. This seems like a modest claim—we're not saying such a being does exist, only that it could. But given the nature of necessary existence, this modest claim has immodest implications.

If a necessarily existent being is possible, then it exists in some possible world. But a necessarily existent being, by definition, exists in all possible worlds. So if it exists in any possible world, it exists in every possible world—including the actual world. The mere possibility of God's existence entails His actual existence.

Evaluating the Argument

The argument is logically valid. If the premises are true, the conclusion follows. The question is whether Premise 1 is true: is maximal greatness possibly instantiated?

The defender of the argument says: why not? The concept of a maximally great being seems coherent. There's no obvious contradiction in the idea of an omnipotent, omniscient, morally perfect, necessarily existent being. If the concept is coherent, it's possible.

The critic responds: the premise is not obviously true. Perhaps maximal greatness is impossible—there's a hidden incoherence in the concept. Or perhaps we simply can't know, from our epistemic position, whether such a being is possible. The premise begs the question if accepting it already requires assuming something close to what we're trying to prove.

Plantinga himself acknowledges that the argument doesn't prove God's existence, since the key premise is not known to be true. But he argues that the premise is reasonable to accept—it's not irrational to believe that maximal greatness is possible. The argument shows that if God's existence is possible, it's actual—which is itself a significant result.

Assessing the Ontological Argument

What should we make of this unusual argument? Several considerations are relevant.

Arguments For

The concept of God involves necessary existence: If God exists, God exists necessarily. A contingent God—a God who might not have existed—would not be the supreme being of classical theism. The concept of God as the greatest conceivable being includes necessary existence. The ontological argument takes this seriously.

The argument illuminates God's unique status: Even if the argument doesn't compel assent, it shows something important: God is not just another being among beings. God's existence, if actual, is necessary. This distinguishes God fundamentally from contingent creatures like us.

The possibility premise is reasonable: Is it really irrational to think a maximally great being is possible? The concept seems coherent. If we have no positive reason to think it's impossible, we may be within our rights to accept its possibility—and thereby its actuality.

Arguments Against

Existence from concepts seems suspicious: Many remain skeptical that we can derive existence from concepts alone. Establishing what exists seems to require looking at the world, not just analyzing ideas. The ontological argument's a priori character makes it suspect.

The possibility premise may beg the question: To know that maximal greatness is possible, we would need to know there's no hidden incoherence in the concept. But how could we know this without already knowing that God exists? The premise may assume what it needs to prove.

Parodies undermine confidence: If similar reasoning could "prove" the existence of other things (perfect islands, necessarily existing pizzas), the argument's form is flawed. While defenders distinguish God's case from parodies, the proliferation of parallel arguments raises concerns.

A Balanced Assessment

The ontological argument probably should not bear the weight of establishing theism by itself. It is too abstract, too controversial, and too easily resisted by those who simply deny the key premise. Unlike cosmological or teleological arguments, it doesn't connect with common experience or scientific evidence.

Yet the argument has value. It illuminates the concept of God—showing that God, if real, is necessarily real. It contributes to a cumulative case—adding one more consideration that makes theism reasonable. And for those who already believe, it provides a profound meditation on what it means for God to be "that than which nothing greater can be conceived."

Using the Ontological Argument

Given its controversial nature, how should the ontological argument feature in apologetics?

Not as a Standalone Argument

The ontological argument is probably not the place to start with most people. Its abstract character makes it difficult to grasp, and it's too easy to dismiss with "I just don't buy it." Other arguments that begin with concrete features of the world may be more effective.

As Part of a Cumulative Case

Within a broader cumulative case, the ontological argument adds value. Once someone accepts that God's existence is possible (perhaps through other arguments), the ontological argument shows that this possibility entails actuality. It raises the stakes of the question: if you admit God is even possible, you're closer to theism than you might think.

For Illuminating God's Nature

The argument is valuable for explaining what Christians mean by God. God is not just a powerful being but the greatest conceivable being—necessarily existent, unsurpassably perfect. The ontological argument unpacks this concept and shows its implications.

For Those Who Find It Compelling

Some people do find the ontological argument compelling. For them, it provides a powerful demonstration that atheism is not just false but impossible—that God's existence is necessary. These individuals can share the argument while acknowledging that others may not find it persuasive.

Conclusion: Contemplating Necessary Being

The ontological argument, whatever its demonstrative power, invites us to contemplate God as necessary being—as the One whose existence is not contingent on anything else, whose non-existence is strictly impossible, who is the self-existent ground of all other existence.

This is the God who revealed Himself to Moses as "I AM WHO I AM" (Exodus 3:14)—the God whose name is pure existence, who simply is, without beginning or end, without dependence or derivation. The ontological argument attempts to show that such a being must exist; at minimum, it illuminates what such a being would be like.

We may not be able to prove God's existence by analysis of concepts alone. But we can recognize that the concept of God—the greatest conceivable being, necessarily existent, unsurpassably perfect—is not one concept among many. It is the concept of ultimate reality, the One on whom all else depends. Whether or not the ontological argument convinces, the God it describes is worthy of our worship, our trust, and our lives.