The ontological argument is an a priori argument claiming that God's existence can be established through reason alone, without relying on observation or experience. Its central claim is that denying God's existence contradicts the concept of God as the greatest conceivable being.
Anselm's argument
Anselm presents the argument in Proslogion. He defines God as "that than which nothing greater can be conceived" and reasons as follows:
- God is the greatest being that can be conceived.
- God exists at least in the understanding, because even someone who denies God understands the concept.
- Existing in reality is greater than existing only in the understanding.
- If God existed only in the understanding, a greater being could be conceived: one existing both mentally and in reality.
- This contradicts the definition of God as the greatest conceivable being.
- Therefore, God exists in reality.
The argument is deductive: if its premises are accepted, its conclusion is intended to follow necessarily. Unlike cosmological or teleological arguments, it does not begin with evidence about the universe.
Major objections
| Philosopher | Objection |
|---|---|
| Gaunilo | The same reasoning might appear to prove that a perfect island exists. This suggests that a definition cannot automatically establish real existence. |
| Descartes | Defends a related argument: existence belongs necessarily to a supremely perfect being, just as having three angles belongs to a triangle. |
| Kant | Argues that existence is not a predicate. Saying that something exists does not add a property to its concept, so existence cannot simply be included in the definition of God. |
A common misconception is that the argument says, "If I imagine something, it must exist." Anselm's narrower claim is that necessary existence uniquely follows from the concept of the greatest conceivable being.
Exam technique
In an IB Philosophy response, reconstruct the argument as clear premises and a conclusion before evaluating it. Focus on whether existence can function as a perfection or predicate, and compare Anselm's reasoning directly with Gaunilo's or Kant's objection rather than merely describing their views.
