Why Did Kant Think the Ontological Proof for God’s Existence Failed?

Kant’s refutation of the ontological proof, if interpreted within the larger context of “Transcendental Dialectic” and not through its standard reading, should have been decisive.

Aug 7, 2023By Fidel Arnecillo, PhD, MA, BA Philosophy, MA Religion

kant ontological proof failed


  • The ontological proof argues for God’s existence based on a definition or concept, captivating many prominent philosophers but also attracting significant criticism.
  • 20th-century analytic philosophers, emphasizing Kant’s assertion that “existence is not a predicate,” believed they had debunked the ontological proof. However, contemporary defenders, notably Alvin Plantinga, revitalized the proof by critiquing Kant’s refutation.
  • Kant’s primary objection to ontological proof is epistemological. He believes reason alone cannot confirm the existence of something, especially if it’s beyond the realm of experience, like God.


Among the classic theistic proofs, the ontological proof is possibly the most interesting. If the premises of the ontological proof are true, then God’s existence can be affirmed a priori (i.e., independently of any experience or purely derived through reasoning). Bertrand Russell famously declared the argument as sound, although later abandoned the proof. Yet, despite its logical appeal, many of those who read it find it problematic, i.e., as a play on words or sophistry. But what are the actual merits of the ontological proof?


The History of the Ontological Proof

anselm canterbury stained glass
Stained glass representation of St Ansem of Canterbury, via Wikimedia Commons.


The ontological proof of God’s existence is a logically valid argument. So, if one has good reasons for thinking that its premises are true, then he or she must recognize its logical force as a theistic proof. However, many philosophers throughout history thought that there was something fundamentally wrong with this kind of proof. For them, it seemed as merely an attempt to cleverly define relevant terms, such as “God.”


The ontological proof draws an existential claim from definitions alone; it leads us to conclude that God exists from how God is defined. This may seem like a play on words, and many are puzzled by the proof’s enduring and persistent appeal among some of the most prominent thinkers in the history of philosophy, including the mathematically inclined ones. Throughout its history, it has managed to captivate some great minds. Such thinkers include Anselm, Bonaventure, Scotus, Descartes, Spinoza, Leibniz, Wolff, Baumgarten, Hegel, Malcolm, Hartshorne, Gödel, Plantinga, and van Inwagen.


This is an impressive list of supporters for a supposedly sophistic attempt at a theistic proof. Furthermore, despite its appearance of being obviously problematic, conclusive criticisms seem out of view, even though the proof has attracted an equally impressive group of detractors. Detractors include Gaunilo, Aquinas, Gassendi, Hume, Kant, Schopenhauer, Frege, Russell, and Oppy.

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Frege, Russell, and the Analytic Reading of Kant on the Ontological Proof

gottlob frege
Gottlob Frege by Gail Campbell, 2016, via Twitter.


In the mid-20th century, a consensus among analytic philosophers sounded the death knell for the proof’s enchanting logical force by pronouncing Kant’s refutation of it as the one that decisively pulled the plug on it.


Due to a preoccupation with the Frege-Russell account of existence as a second-order property of concepts or propositional functions (rather than a property of individuals), analytic philosophers interpreted Kant’s refutation of the ontological proof as primarily having to do with his acceptance of the “existence-is-not-a-predicate” mantra. That became the standard reading of Kant’s refutation of the ontological proof.


Based on their reading of Kant, the argument is thought to go something like this: the ontological proof presupposes that existence is a property of an individual. However, existence is not a property of an individual. So, the ontological proof fails.


alvin plantinga
Photograph of Alvin Plantinga via Templeton Prize / John Harrison


But such confidence in Kant’s refutation of the ontological proof did not last for long. Contemporary defenders of the ontological proof, such as Alvin Plantinga, seem to have shattered such confidence through their reevaluations of Kant’s refutation of the ontological proof as interpreted through its standard reading.


After Plantinga’s critique of Kant’s refutation of the ontological proof, the ontological proof flourished once again as a viable theistic proof. This is not meant to diminish the role of Norman Malcolm and Charles Hartshorne in its revival in the 20th century; but Plantinga consistently targeted Kant’s refutation of it (to explore his arguments, see “Kant’s Objection to the Ontological Proof,” Journal of Philosophy volume LXIII, no.19 (October 13, 1966): 537-546; Alvin Plantinga, God, Freedom, and Evil (Grand Rapids: William B. Eerdmans Publishing Company, 1977), 92-98; Alvin Plantinga, God and Other Minds: A Study of the Rational Justification of Belief in God (Ithaca: Cornell University Press, 1967)).


It’s understandable why Plantinga targeted Kant’s refutation of it, considering that analytic philosophers in the mid-20th century generally treated Kant’s refutation as decisive and that Plantinga would eventually be primarily responsible for the contemporary reconstruction of the proof. So, the attempt to discredit Kant’s refutation would be essential for resurrecting the proof. A careful reading of the relevant sections of Kant’s first Critique (CPR hereafter) and a survey of relevant secondary literature, like the works of Allen W. Wood, Michelle Grier, and Henry Allison, show that the standard reading of it is an inadequate reading of Kant’s refutation.


The Standard Reading of Kant’s Refutation of the Ontological Proof

god appearing
God appearing to Isaac by Marco Dente, after Raphael (Raffaello Sanzio or Santi), ca. 1515–27. Via the Met Museum.


In a nutshell, here’s the standard reading of Kant’s refutation (SR hereafter):


(Premise 1) The ontological proof, in order for it to work, must assume that existence is a property that must be necessarily predicated of God.

(Premise 2) However, existence is not a real predicate.

(Conclusion) Therefore, the ontological proof fails.


With the status of a cliché, the second premise is usually treated as the crux of Kant’s refutation of the ontological proof. The standard reading assumes that Kant is primarily concerned with the logical failure of the ontological proof, i.e., with the logical function of the predicate “exists.”


Many contemporary philosophers of religion, such as John Hick (Philosophy of Religion 4th edition, 1990), Alvin Plantinga, Peter van Inwagen (“Necessary Being: The Ontological Argument” in Arguing About Religion, edited by Kevin Timpe, 2009), and Stephen T. Davis (God, Reason and Theistic Proofs, 1997), use SR to encapsulate Kant’s refutation of the ontological proof in his Critique of Pure Reason. Each of them claims that the second premise is the crux of Kant’s refutation. Surprisingly, some major Kant scholars also appear to accept SR. For example, in the introduction to Paul Guyer’s and Allen Wood’s translation and edition of CPR, they summarize Kant’s refutation of the ontological proof in the following way:


First Kant attacks the ontological argument, holding that since existence is not a property and therefore not itself a perfection, it cannot be included among the contents of the idea of God, and cannot be inferred from the idea alone. (p.18)


kromer a priori
A Priori by James Kroner, via Carmel Visual Arts.


Nathan Salmon makes a similar claim about Kant’s refutation. According to Salmon,


The credit for having located the fallacy in the [ontological] argument is often attributed to Kant, who purported to debunk the argument with his observation that existence is not a predicate that can be legitimately included in the definition or concept of something. Kant’s refutation is widely regarded as conclusive, or at least sound…

(Nathan Salmon, Metaphysics, Mathematics, and Meaning: Philosophical Papers I (New York: Oxford University Press, 2006), p. 18.


Here’s another example: Lawrence Nolan, a Descartes scholar, accepts SR in his attempt to defend Descartes’ ontological proof from Kant’s refutation. It appears that SR is a well-accepted standard reading of Kant’s refutation. It is important as a point of interpretation to correct SR for a proper reading of Kant’s refutation but also, and more importantly, for a proper estimation of its philosophical and historical reach, notably its possible refutation of the classic formulations of the ontological proof.


Is Kant’s Ontological Proof Linked to Kant’s Epistemology? 

critique pure reason kant
Title page of the Critik der reinen Vernunft by Immanuel Kant, 1781, via kettererkunst.de.


Without putting Kant’s refutation of the ontological proof within the context of Kant’s general project of attacking rationalist metaphysics in the “Transcendental Dialectic,” there is a tendency to treat Kant’s refutation of the ontological proof in isolation from the more general arguments made by Kant. This kind of reading leaves out the epistemological dimension of Kant’s refutation, which is at its core. The standard reading completely ignores the epistemological dimension.


Some Kant scholars, like Uygar Abaci, think that Kant’s refutation can be isolated from Kant’s larger project in the Critique of Pure Reason because Kant has a particularly specific task in his refutation that can be treated independently of the larger project. According to Abaci,


Whether Kant’s refutation works in itself as an argument in isolation from the critical framework is a question that is worth to ask here. At the final analysis, the proponent of the ontological proof may always reject to endorse Kant’s critical philosophy, if the refutation is presented as essentially dependent on it.

Uygar Abaci, “Kant’s Theses on Existence,” British Journal for the History of Philosophy 16, no. 3 (2008): 559-593.


immanuel kant lopez
Emmanuel Kant by Julissa Lopez, 2012, via the artist’s Behance.


While Abaci’s position is understandable, Kant’s refutation should not be isolated from his wider project. By isolating it from the larger project, one potentially breaks the continuity between Kant’s arguments in “Transcendental Dialectic” and Kant’s refutation (a subsection in the Critique of Pure Reason’s “Transcendental Dialectic”). For exegetical purposes, the isolation of one from the other should be unacceptable. Allison stated something that seems to capture what I have in mind:


This is not, of course, to claim either that Kant is correct in his denial that ‘existence’ is a real predicate or that this denial cannot also be made on non-Kantian grounds. It is, however, to suggest that Kant’s critique of the ontological argument is deeply rooted in some of the central tenets of his epistemology and cannot be neatly separated from this context.

Allison, Kant’s Transcendental Idealism: An Interpretation and Defense, 416-417.


path reason zimmerman
The Path of Reason by David Zimmerman, 2015, via Fine Art America.


For Kant, the faculty of reason, as distinguished from the faculty of understanding, is responsible for the transcendental illusion, which includes theistic illusion (i.e., the fallacious belief in the objective existence of God). Such illusion, for Kant, is natural, unavoidable, and inextinguishable.


According to Kant, this “theistic illusion” arises because reason naturally and inevitably extends its reach beyond the scope of possible experience. Reason pretentiously determines the objective existence of some things (including God) outside the bounds of possible experience. But, for Kant, reason cannot legitimately go beyond the bounds of possible experience, even though it ventures beyond them nonetheless (thanks to Patricia Easton for her comment). That leads to transcendental illusion.


Reason does not directly deal with the realm of possible experience. Rather, reason directly deals with the understanding, providing the principles that unify the manifold of cognitions of the understanding. Considering the lack of direct relation between reason and the realm of possible experience, reason on its own cannot make judgments about existence (i.e., what exists or what does not exist).


Reason and Existence: The Real Reason Kant Believed the Ontological Proof to be Impossible

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God the Father by Ludovico Mazzolino, 1510, via Fine Art America.


The fact that the ontological proof argues for God’s existence from the mere use of reason, extending what we can claim to exist beyond the scope of possible experience, implies the proof’s impossibility. Therefore, Kant’s problem with the ontological proof is not primarily about the logical function of “exist,” which has peripheral significance in relation to Kant’s overall project in the “Transcendental Dialectic.” Rather, it has more to do with the lack of any sensible or experiential ground for any knowledge of God’s existence.


Kant’s problem with the proof is primarily epistemological in nature, considering that God’s existence is beyond the scope of sensible cognition. For Kant, the concept of God is merely an idea. A mere idea cannot really tell us anything about what exactly exists. We cannot rule out the possible existence of anything a priori, but we cannot even confirm the possible existence of anything either. That’s due to the fact that there is nothing given in sensible cognition. Hence, the ontological proof is not possible, since it tries to prove the existence of God from the mere concept of God.


kant minca
Immanuel Kant by Victor Minca, 2014, via Fine Art America.


Another way to make this point draws on what Peter W. Ross and Dale Turner refer to as two different kinds of existence problems (see “Existence Problems in Philosophy and Science,” 2013). Ross and Turner propose a strategy for categorizing existence problems as philosophical or scientific based on the tractability or intractability of the relevant causal relations.


A philosophical existence problem involves a putative entity (e.g., God) whose existence is elusive (at least currently undetected and intractable). A scientific existence problem involves tractable causal relations that offer evidence, although not conclusive, for a putative entity’s existence.


For example, the idea of a multiverse is “described as encompassing indefinitely many pocket universes each produced by a mechanism such as eternal inflation…it is controversial whether the multiverse hypothesis is a scientific hypothesis.” But Ross and Turner argue that, “since physicists are in the process of formulating a tractable causal relation between other pocket universes and their signatures, the multiverse hypothesis is scientific.”  Hence, existence problems involving tractable causal relations are scientific, whereas existence problems involving intractable causal relations are philosophical.


Kant has similar concerns in his account of existence in general and in his refutation of the ontological proof. For Kant, existence problems cannot be philosophical (or at least cannot be purely philosophical), since the determination of the existence of anything must have some connection with possible experience. But the ontological proof attempts to treat the existence problem pertaining to God as purely philosophical. For Kant, that’s impossible.

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By Fidel ArnecilloPhD, MA, BA Philosophy, MA ReligionFidel teaches philosophy at California State University, San Bernardino, and California State Polytechnic University, Pomona. His primary academic interests include modern philosophy (esp. Kant), philosophy of religion, moral/political philosophy, and Christian theology. He received his Ph.D. and M.A. in philosophy from Claremont Graduate University, M.A. in religion from Yale University Divinity School, and B.A. in philosophy from Point Loma Nazarene College. He loves playing basketball, using Facebook for digital activism, watching all sorts of movies on Netflix, and spending lots of time with his son and wife. He is also the pastor of Symposia Covenant Church (Ontario, California).