The Anselmian argument claims that God's existence follows necessarily from the very concept of God as "that than which nothing greater can be conceived." The argument's inferential structure moves from this definition to the claim that such a being must exist in reality, not merely in the understanding. Anselm reasons that if this greatest conceivable being existed only in the mind, we could conceive of a greater being—one that exists both in the mind and in reality. Since this would contradict the initial definition, the greatest conceivable being must exist in reality. The argument thus attempts to demonstrate God's existence through pure conceptual analysis, without appeal to empirical premises.
Anselm of Canterbury (1033-1109) first articulated this argument in his Proslogion (1077-1078), specifically in chapters 2-4. The argument emerged within the context of monastic meditation, as Anselm sought a single, self-evident proof of God's existence. Key medieval defenders included Bonaventure in his Commentary on the Sentences and Duns Scotus, who offered a coloratio (refinement) in his Ordinatio. The argument experienced renewed interest in the modern period through Descartes, Leibniz, and Hegel, though these philosophers developed distinct versions. In the 20th century, Charles Hartshorne in The Logic of Perfection (1962) and Norman Malcolm in "Anselm's Ontological Arguments" (1960) revived specifically Anselmian interpretations, distinguishing Anselm's original formulation from later variants.
The most famous objection came from Gaunilo of Marmoutiers in his On Behalf of the Fool, arguing that parallel reasoning would prove the existence of a perfect island. Anselm responded in his Reply to Gaunilo that the argument applies uniquely to necessary existence, not to contingent perfections. Kant's critique that "existence is not a predicate" challenged whether existence adds to a concept's content. Contemporary Anselmians like Katherin Rogers in The Anselmian Approach to God and Creation (1997) respond that Anselm's argument concerns modes of existence (necessary vs. contingent) rather than existence as a property. The objection that conceivability doesn't entail possibility is addressed by defenders who argue that maximal greatness, properly understood, includes coherence as part of its very concept.
The Anselmian argument differs from the Cartesian version in its emphasis on God as the greatest conceivable being rather than as possessing all perfections. Unlike the modal ontological argument, it doesn't explicitly employ possible worlds semantics. Where Gödel's proof uses formal logic and mathematical properties, Anselm's remains intuitive and meditative. The Anselmian formulation is distinguished by its focus on the phenomenology of thought—what happens when we truly attempt to think the greatest conceivable being—rather than on formal deduction from divine attributes.