The philosopher and theologian Anselm of Canterbury famously argued that God’s existence can be proven via reason alone, without the appeal to observation, experience, or evidence. According to Anselm, if God is a “being than which nothing greater can be conceived,” then God must necessarily exist in reality, because a being that exists in reality is greater than a being that exists only as an idea in the mind. Since God is the greatest imaginable being, He cannot be confined to the land of make-believe. And presto, God exists!
Intuition tells us something is wrong here—that the argument is far too good to be true. But it’s not immediately clear what that something is. As Bertrand Russell put it, “The argument does not, to a modern mind, seem very convincing, but it is easier to feel convinced that it must be fallacious than it is to find out precisely where the fallacy lies.”
Luckily enough, the eighteenth-century German philosopher Immanuel Kant, in the Critique of Pure Reason, has done all the hard work for us. Not only did he identify the ontological argument’s fatal flaw, he also demonstrated how all arguments for God’s existence ultimately succumb to the same error. Kant, in other words, dismantled the rational basis for belief in God by showing that the major arguments for God’s existence ultimately reduce to disguised versions of a single, fundamentally flawed argument.
It’s an extraordinary yet vastly underappreciated achievement. Let’s see how he pulled it off.
We can begin with a simple observation. In everyday language, it makes sense to compare the attributes or properties of objects. You can say, for example, that one knife is “greater” than another if the blade is sharper, the handle is more ergonomic, or the steel is of higher quality. But it would be a bit bizarre for you to make the claim that one knife is greater than another because it exists.
Existence, in this manner of speaking, is not a property; rather, it’s a prerequisite for the instantiation of any properties at all. The knife cannot be sharp, and the handle cannot be ergonomic, unless the knife already exists. Its existence is not another property of the knife; it is what makes the attribution of properties to an actual knife possible in the first place.
Think about it another way. You are perfectly capable of imagining a “knife than which none sharper can be imagined,” but you shouldn’t expect your act of imagination to actually conjure this knife into existence, any more than you should expect to improve your financial situation by adding a few zeros to the end of your printed bank balance. Although this would be nice, reality does not so easily bend to our wishes.
Properties simply do not depend on existence, nor existence on properties. They belong to separate and mutually exclusive categories. One hundred dollars in your hand and one hundred dollars in your imagination have the same properties. Yet existence doesn’t add or remove any properties whatsoever; it merely determines whether you can put them to use in the real world.
Similarly, an omnipotent God in reality and an omnipotent God in your imagination may have identical properties. But for God to exist in reality, there must be some way to distinguish that existence from mere imagination—some connection to experience or evidence. Otherwise, God exists only in your mind, alongside the millions of dollars accruing interest in your imaginary bank account.
The upshot for Kant is that, while it is legitimate to say that if God exists, he must have so-and-so properties (omnipotence, omniscience, etc.), it still leaves the question of God’s actual existence entirely unresolved. The reason should now be clear: you cannot think things into existence, whether they be the sharpest knife, the perfect island, the largest savings account, or a being than which none more evil can be imagined—the Devil. These are all, until given empirical grounds for their existence, imaginary.
Today, few people would argue that Kant did not lay the ontological argument to waste—and that Anselm was, in fact, correct. But what may not be immediately obvious is that all arguments for God’s existence, at bottom, contain the same fatal flaw.
Consider the cosmological argument. One form of the argument goes like this: since everything that begins to exist has a cause, and the universe began to exist, then the universe itself must have a cause. For Kant, all that this proves—if it in fact proves anything—is the existence of a first cause. But the idea that this first cause must be God—in the form of a necessary, perfect being—requires that we smuggle the ontological argument back in as a hidden premise.
We can see this clearly for ourselves. The cosmological argument begins on plausible evidential grounds. The cause-and-effect relationships we experience each day are used as empirical evidence, and only then analogized to the universe at large. So far, at least, the argument is empirically motivated: it begins with causal relationships we encounter in experience and extends them to the universe as a whole. Whether that analogy is legitimate is another question (David Hume thought it wasn’t), but at least we have an attempted anchor to the actual world.
But look at what happens next. The supposed establishment of a first cause is precisely where empiricism ends and Anselm makes his inglorious return. To leap from a hypothesized ultimate cause to the perfect being of classical theism, you need an a priori argument—one that establishes the necessary existence of that being. In other words, you need the ontological argument (or some variation thereof).
We’ve now come full circle. Without the ontological argument, there’s no reason to suppose that this first cause must be anything more than a material cause—or that it has any particular concern for humanity, as in deism. Indeed, the imperfections and evil in the world seem far more consistent with a noninterventionist deist God—one who wound up the universe like a clock and then simply let it run.
But do we even need to go this far? If we’re content to terminate an infinite regress of causation at some arbitrary point, the principle of parsimony urges us to simply stop at the necessary existence of the material world itself. Hence, the God hypothesis is unnecessary and redundant.
Cosmological arguments, then, contain the seeds of their own destruction. But what about teleological, or design, arguments? Do they fare any better?
Not a bit. They suffer from the same problem. Like cosmological arguments, they begin as empirical arguments, reasoning by analogy from the apparent design of human artifacts to the universe as a whole. But even if the analogy succeeds, it leaves us knowing almost nothing about the designer’s nature. There might be one designer or many, or the designer might be indifferent, incompetent, or even malicious. In either case, the world simply doesn’t provide us with this information, and we are left to argue, on a priori grounds, whether this grand designer has any special care for humanity, or else is entirely indifferent.
Kant’s case is therefore devastating for rational theology. He has shown us that, however the theist gets to a first cause or grand designer—whether through teleological or cosmological arguments—the final step is the same: the conjuring of the God of theism into existence using reason alone, just as Anselm attempted to do. Yet we have no more reason to accept any of these arguments than we do Anselm’s long-discredited “proof.”
Kant, interestingly enough, did not regard this as the death of religion. His famous declaration that he had “found it necessary to deny knowledge, in order to make room for faith” makes clear that he hoped to preserve religion on grounds other than reason. But that was precisely the point: once reason could no longer establish God’s existence, faith had to occupy the territory reason had abandoned. Whether this is a legitimate, or even desirable, project, I leave to the reader. Yet believing something without good reason or evidence hardly seems like a virtue—especially when doing so leaves one susceptible to deception and delusion.
In the previous post, The Illusion of Design, we saw how David Hume attacked the empirical route to God, exposing the design argument as a weak analogy and, therefore, incapable of providing empirical justification for God’s existence.
In this article, we’ve seen how Kant attacked the opposite, a priori route, exposing the vacuity of ontological arguments. Taken together, Hume and Kant left the traditional proofs for God with nowhere left to go: Hume showed that experience cannot get us to the God of classical theism; Kant argued that pure reason cannot get us there either.
The two great routes from reason to God have thus been blocked from opposite directions, leaving faith to carry a burden it is unequipped to bear. In that sense, Hume and Kant did more than dismantle two arguments—they helped awaken the modern mind from its dogmatic slumber.
References and Further Reading
“Anselm: Proslogium.” Internet Medieval Sourcebook. Fordham University. Accessed August 24, 2026. https://sourcebooks.web.fordham.edu/basis/anselm-proslogium.asp.
Boissonneault, Ryan. “The Illusion of Design: How David Hume (Not Darwin) Dismantled the Strongest Case for God.” Fighting the Gods, August 21, 2026.
Hume, David. Dialogues Concerning Natural Religion. Mineola, NY: Dover Publications, 2012.
Kant, Immanuel. Critique of Pure Reason. Translated by Werner S. Pluhar. Indianapolis: Hackett Publishing Company, 1996.
Yovel, Yirmiyahu. Kant’s Philosophical Revolution: A Short Guide to the Critique of Pure Reason. Princeton, NJ: Princeton University Press, 2018.