What is the ontological argument?
Question 60102
The ontological argument is the most philosophically demanding of the classical arguments for God’s existence, and probably the most disputed. Unlike the cosmological or teleological arguments, which move from features of the external world to a conclusion about God, the ontological argument attempts to establish God’s existence from the concept of God alone — from pure reason, without any appeal to observation or experience. Its longevity across nearly a thousand years of philosophical debate suggests it deserves more serious engagement than the dismissal it sometimes receives.
Anselm’s Original Formulation
Anselm of Canterbury formulated the argument in his Proslogion, written around 1078. He defined God as “that than which nothing greater can be conceived.” The argument then proceeds as follows. We can conceive of such a being. Now: does this being exist only in the mind, or also in reality? A being that exists in reality is greater than one that exists only as a concept. If God existed only in the mind, we could conceive of something greater — namely, a God who also exists in reality. But this contradicts the definition, since God is already defined as that than which nothing greater can be conceived. Therefore God must exist in reality.
The monk Gaunilo of Marmoutiers offered an immediate counter-argument, which has been repeated in various forms ever since: using the same logic, one could prove the existence of a perfect island. Simply define the most excellent island conceivable — and then argue that it must exist in reality, since a real island is greater than an imaginary one. Anselm’s response was that the argument applies specifically to a being whose existence is necessary, not to contingent things like islands. A perfect island, however magnificent, might not have existed and might one day cease to exist. God, as defined, cannot be like that.
Kant’s Objection and the Modern Response
Immanuel Kant offered what became the most influential philosophical objection: existence is not a predicate. Adding “exists” to the description of a being does not make that being greater or more perfect, because existence is not a property in the way that power or wisdom are properties. You do not increase the quality of something by saying it also exists. This objection has considerable force against Anselm’s original formulation and is widely accepted among philosophers.
The modal ontological argument, developed in the twentieth century principally by Alvin Plantinga, attempts to sidestep Kant’s objection by working with the concept of possible worlds rather than direct existence claims. Plantinga argues that if it is even possible that a maximally great being exists — a being possessing maximal power, knowledge, and goodness in every possible world — then such a being actually exists. The key move is this: a being whose existence is merely contingent (it exists but could have failed to exist) would be less than maximally great, because its greatness could have been absent. A being that is truly maximally great must exist necessarily, in every possible world. If such a being is possible, it is necessary. And what is necessary is actual.
Plantinga himself describes his version as establishing that it is rational to believe in God rather than demonstrating God’s existence in a way that compels assent. The argument’s force depends on accepting the key premise — that a maximally great being is genuinely possible rather than self-contradictory — and this is something that can reasonably be disputed.
What to Make of the Argument
The ontological argument has attracted brilliant defenders and equally brilliant critics across nearly a millennium, which itself indicates it is not the obvious nonsense it is sometimes portrayed as. Descartes, Leibniz, and Plantinga have defended versions of it; Kant, Hume, and Bertrand Russell have criticised it. The fact that neither side has definitively settled the question suggests the argument touches something genuinely difficult about the relationship between logical concepts and reality.
From a biblical standpoint, it is worth noting that Scripture does not argue for God’s existence from philosophical first principles. “In the beginning, God” — Genesis 1:1 — is a statement, not a demonstration. The psalmist’s declaration that “the fool says in his heart, ‘There is no God'” (Psalm 14:1) does not treat atheism as primarily an intellectual error to be corrected by better reasoning. It treats it as a moral and volitional posture — a refusal to acknowledge what is already, in some sense, known. Romans 1:18-20 similarly describes the knowledge of God as something already present in human beings and actively suppressed, not something that needs to be argued into existence from scratch.
This does not make philosophical argument worthless. It clarifies its proper role. Philosophical arguments work best not by creating knowledge of God from nothing but by exposing the inadequacy of the alternatives and removing intellectual objections that are functioning as cover for a volitional refusal. The ontological argument, at its best, does this: it shows that the concept of a necessarily existing being is not incoherent, and that dismissing God as merely an imaginary construct carries its own philosophical difficulties.
So, now what?
The ontological argument is unlikely to be the instrument most Christians reach for in ordinary evangelistic conversation, and it would be dishonest to present it as a watertight proof that settles all reasonable doubt. Its value is more specific: for those who engage seriously at a philosophical level, it demonstrates that the concept of God as a necessary being is not a category error or a logical impossibility. It also illustrates that no argument, however valid its logical form, operates on a mind that is entirely neutral. The heart that does not want God will find grounds for scepticism about the premises. The heart that has been opened by the Spirit will find that the evidence, philosophical and otherwise, converges on a conclusion it already, in some deeper sense, recognises.
“The fool says in his heart, ‘There is no God.’ They are corrupt, they do abominable deeds; there is none who does good.” Psalm 14:1
Bibliography
- Anselm of Canterbury. Proslogion. Translated by M.J. Charlesworth. University of Notre Dame Press, 1979.
- Plantinga, Alvin. The Nature of Necessity. Clarendon Press, 1974.
- Plantinga, Alvin. God, Freedom, and Evil. Eerdmans, 1977.
- Craig, William Lane and Moreland, J.P. Philosophical Foundations for a Christian Worldview. InterVarsity Press, 2003.
