Can You Argue from an Idea to God?

Foundations

A Strange Argument

• Most arguments for God start from the world — causes, design, morality.
• The ontological argument starts from the concept of God alone.
• It tries to reason from idea straight to reality.
• It is the most debated and slippery of the theistic arguments.

Key idea: Unique among the arguments: it uses no evidence from the world — only the idea of God itself.

Source: History of philosophy of religion.

Anselm

Anselm's Version (1078)

• God is “that than which nothing greater can be conceived.”
• A being that exists in reality is greater than one existing only in the mind.
• So if God existed only as an idea, a greater being would be conceivable — a contradiction.
• Therefore, Anselm argues, God must exist in reality.

Useful fact: Anselm defined God as the greatest conceivable being — then argued such a being can't exist only as an idea.

Source: Anselm, Proslogion (1078).

Anselm

Why It's Intriguing

• It is a single, self-contained move.
• If it works, it proves a necessary being by reason alone.
• It has fascinated philosophers for over 900 years.
• Even critics struggle to say exactly where it fails.

Source: Standard histories of the argument.

Objections

Gaunilo's “Perfect Island”

• A monk, Gaunilo, replied in Anselm's own day.
• Imagine the “greatest conceivable island” — does defining it make it exist?
• If not, why should defining the greatest being make God exist?
• This parody is the classic rejoinder.

Classic reply: Gaunilo: you can't define things into existence — or the “greatest island” would have to be real too.

Source: Gaunilo, On Behalf of the Fool.

Objections

Anselm's Answer

• Islands are contingent — they could always be greater, or not exist at all.
• Only a necessary being is the kind of thing the argument concerns.
• So the island parody doesn't transfer.
• Whether this fully answers Gaunilo is still debated.

Source: Anselm's reply to Gaunilo.

Objections

Kant's Objection

• Immanuel Kant argued that “existence is not a predicate.”
• Saying a thing exists adds no property to its concept.
• So “greatness” can't include “existence” the way the argument assumes.
• This is the most influential criticism of all.

Useful fact: Kant's famous reply: existence isn't a property a thing can “have” — so you can't build it into a definition.

Source: Immanuel Kant, Critique of Pure Reason (1781).

Modern

Plantinga's Modal Version

• Alvin Plantinga restated the argument using possibility and necessity.
• If it is even possible that a “maximally great being” exists, then it exists.
• The argument is logically valid; the debate is over its key premise.
• Plantinga himself calls it a reason for belief, not a proof for all.

Key idea: Plantinga's modern version is valid — everything hangs on whether a maximally great being is even possible.

Source: Alvin Plantinga, The Nature of Necessity (1974).

Modern

The Sticking Point

• Is a “maximally great being” genuinely possible?
• If yes, the argument goes through; deny its possibility and it stalls.
• One can grant or deny that premise without obvious contradiction.
• So the argument may not compel a determined skeptic.

Honest note: Plantinga's argument doesn't force assent — a skeptic can simply doubt the crucial “it's possible” premise.

Source: Standard assessments of the modal argument.

Honest Limits

Valid but Unpersuasive?

• Many philosophers find it valid yet unpersuasive.
• It can feel like a trick even when no flaw is obvious.
• It reaches a necessary being, not a specific religion.
• It works best alongside the other arguments, not alone.

Key idea: A fascinating argument that proves little to the unconvinced — strongest as part of a cumulative case.

Source: Reflected across the literature.

Conclusion

The Big Takeaway

• The ontological argument reasons from the idea of God to God.
• Anselm, Kant, and Plantinga mark its main turns.
• It is logically slippery — valid forms exist, but the premises are contestable.
• It is more a profound puzzle than a knock-down proof.

In one line: The boldest argument for God — endlessly debated, and never quite dead.

Source: Anselm; Kant; Plantinga.