The ontological argument for the existence of God is the most famous and has been heavily analyzed and debated ever since its formulation by St. Anselm of Canterbury in the 11th century.[i] In its most common form, the ontological argument defines God as a being of which nothing greater can be conceived. Given this, there are two possibilities. First, this being exists both in reality and in our mind. Second, this being only exists in our mind. The ontological argument then asserts that a being that exists is greater than a being that does not exist. Therefore, if this being only exists in our mind, there is a conceivable being that is greater, a being that both exists in our mind and exists in reality. Since this is a logical contradiction, a being of which nothing greater can be conceived must exist. This version of the ontological argument is logically formulated as follows:
Ontological Argument
P1. God is understood as a being than which nothing greater can be conceived.
P2. A thing exists either in understanding only or in both understanding and reality.
P3. It is greater to exist in both understanding and reality than in reality only.
C1. Therefore, if God exists only in understanding, then something greater can be conceived, namely, a God that exists in both understanding and reality.
C2. Therefore, God cannot exist only in understanding.
C3. Therefore, God must exist in both understanding and in reality.
This formulation is formally and logically valid. If one accepts the three premises, one must also accept the three conclusions. The remainder of this section will address this version of the ontological argument, but it should be known that Anselm had an additional formulation based on the concept of God as a maximally perfect being rather than something than which nothing greater can be conceived.
Since the logic of the ontological argument is sound, its conclusions can only be challenged by challenging one-or-more of the premises. Premise two is non-controversial, leaving the first and third premises as the focus of whether the conclusions should be believed.
The first possible criticism of P1 is that humans cannot conceive of God, as God in ineffable and we can only know God to the extent that He reveals Himself to us. Though true, the ontological argument only requires that we understand God as defined in P1. Douglas Groothuis explains the requirements of this understanding as follows: “A Perfect Being is a being who possesses every property it is better to have than to lack and who possesses this array of compossible excellent properties to the utmost degree (or to their intrinsic maximum value).”[ii] It can be argued that humans cannot conceive of a being with these characteristics, but this argument is somewhat weak compared to other arguments.
The most famous and serious criticism of the ontological argument is from Immanuel Kant. Kant argues that the ontological argument requires existence to be a predicate for God. That is, the ontological argument requires using the concept of “God exists.” But Kant reasons that existence cannot properly be used a predicate for God since existence adds nothing to the concept of God. One can think of many abstract concepts that exist only in the mind but not in reality. In the same way, God could simply be an abstract concept that does not exist in reality. Formally, Kant asserts that “exists” in “God exists” is not a genuine predicate. If existence is not a genuine predicate in the ontological argument, the argument fails.[iii] But Groothuis argues that existence can properly be understood as a genuine predicate in the ontological argument, “since the matter of God’s existence is a legitimate question, like the ontological status of the animals in the children’s story … These things are possibly existing things, so existence is an appropriate and meaningful predicate concerning their ontological status.”[iv] Although perhaps philosophically interesting, diving this deep into the grammar of logical arguments is typically not useful in an apologetic sense.
A more accessible critique of the ontological argument comes from the Benedictine monk Gaulino, who uses the logic of the ontological argument to “prove” the existence of a perfect island, because it would not be perfect if it only existed in the mind. Gaulino writes:
“If … someone wishes thus to persuade me that this island really exists beyond all doubt, I should either think that he was joking, or I should find it hard to decide which of us I ought to judge the bigger fool – I, if I agreed with him, of he, if he thought that he had proved the existence of this island with any certainty.”[v]
Anselm’s response to Gaulino is that the ontological argument cannot properly be applied to finite things since something infinite is always greater than something finite, and an infinite island cannot be conceived. The obvious reply is that humans cannot properly conceive of an infinite God either. For all of these complexities, it is not clear whether the ontological argument has ever changed anyone’s opinion about the existence of God (to my knowledge). It is nevertheless important for the Christian apologist to have familiarity with the ontological argument due to its well-known nature.
[i] Anselm presents his two versions of the ontological argument in his Proslogion.
[ii] Douglas Groothuis, Christian Apologetics: A Comprehensive Case for Biblical Faith, 2nd ed., Downers Grove, IL: InterVarsity Press, 2022: 186.
[iii] Kant’s criticism of the ontological argument can be found in his Critique of Pure Reason.
[iv] Douglas Groothuis, Christian Apologetics: A Comprehensive Case for Biblical Faith, 2nd ed., Downers Grove, IL: InterVarsity Press, 2022: 189.
[v] Gaulino wrote this in his essay, “A Reply on Behalf of the Fool.” I used the translation found in Stumpf and Abel’s Elements of Philosophy, 4th ed.: 106.
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