Introduction
When I was studying Martin Heidegger’s Being and Time a few years ago I came across a brief essay by Hannah Arendt entitled “What Is Existential Philosophy?” She had several interesting insights that went beyond the usual survey. Her most intriguing point was that German philosopher Immanuel Kant paved the way for existentialism by “shattering” the unity of thought and being. I was curious to revisit this so I made a mental note to get back to Arendt after I finished writing about Heidegger. And so here I am.
In this essay I want to unpack Arendt’s point and show how we get from Kant to existentialism. To do that we need to understand what is meant in philosophy by “the unity of thought and being.” This is one of the oldest assumptions in Western philosophy. As early as the fourth-century BCE, Parmenides declared “to think and to be are the same thing” [1]. The ancients believed the world was rational—that it was perfectly structured according to intelligible, logical principles—and that this rational order began with the divine. Aristotle develops the idea that the Prime Mover (God) is pure actuality, whose activity is the contemplation of its own intellect:
“[T]hought thinks itself through participation in the object of thought; for it becomes an object of thought by the act of apprehension and thinking, so that thought and the object of thought are the same, because that which is receptive of the object of thought, i.e. essence, is thought” [2].
It’s a dense passage, but the gist is simple enough: God is a self-thinking thought. Or put differently, in the divine mind thought and being coincide perfectly. Later thinkers extend this unity outward. Plotinus built a hierarchy in which all beings participate in the world’s intelligibility according to their place in the cosmic structure. Aquinas followed this line of reasoning and argued explicitly that “being also is in the things and in the intellect” [3]. The shared assumption was that our minds and the world mirrored each other’s rational structure, which guaranteed that knowledge was possible.
Kant breaks that long-standing unity. He argues that things-in-themselves—the really real objects that exist independent of us—are inherently unknowable. What we know are objects as they appear to us by way of the structures of our own minds:
“Up to now it has been assumed that all our cognition must conform to the objects… [let us assume instead] that the objects must conform to our cognition” [4].
Kant compares this reversal to Copernicus, who explained celestial motion by putting the observer in motion rather than the stars. The result is we are no longer passive spectators of an independent world. Instead, we play an active role in shaping what is given to us in cognition. Arendt’s point is that this move severs the old unity: the mind and the world no longer share a common rational structure. After Kant, we find ourselves cut off from a world that once supplied meaning, and instead we must impose meaning ourselves. That shift opens the door to existentialism, where the burden of finding meaning falls squarely on the individual.
The Ancient Order
It was not always this way. For the ancients, the gods and goddesses carved order out of material chaos. They gazed down at us like we were pawns on their chessboard, backing their chosen heroes and punishing their enemies. Our wars were echoes of their divine quarrels with one another. And all the while the Fates shaped our destiny so it mattered little what choices we made anyway. The world was divided physically into two parts. There was our flawed material world here below and up above the perfect firmament where the heavenly beings, stars, and planets circled just overhead.
This Greek and Roman cosmology largely carries on into early Christianity. Only now there is a single Creator who wills order into being out of nothingness. Our lives are part of His cosmic divine plan. A Great Chain of Being runs all the way from the lowest depths of Hell on up to the highest of the seven heavens. Everything that happens is ordained, purposeful, and for the greater good. And the world is external and objective. It can be known. Objects are given to us and truth is a function of the correspondence between the known external world and our perception of it.
Something darker kept coming to the surface. Even though we believed the world to be logically structured, there ran a persistent worry that we were ill-suited for it. There has always been an unsettledness that drove us toward various metaphysical theories in order to explain how we fit into the grand scheme of things. Theological reflection begins in this anxiety. In the 6th century BCE, the Buddha taught that we are dissatisfied in life. We all feel a profound sense of unease and do not know our place in the world. This is his First Noble Truth. And consider this short saying of Jesus:
“Foxes have dens, and birds of the sky have nests; but the son of Adam [ho huios tou anthrōpou] has nowhere to rest his head” [5].
If we interpret this to mean that Jesus is oddly speaking of himself in the third person, then he seems to be lamenting his own homelessness. I prefer a richer interpretation. In Aramaic, “son of Adam” [bar adam] means “human being” or humanity as a whole. Jesus is saying that, while everything else in the world seems to be right at home we are not. Something is not quite right with us. We are restless.
My point is that our restlessness is ancient. Despite our view of a rational cosmos, unease and anxiety have always been a part of the human condition. To counter such anxiety, we want to feel that our lives fit into some larger purpose that is both noble and meaningful. But what happens when that meaning falls away? To answer that we have to return to Kant in some detail.
Kant’s Destruction
As I said at the outset, Arendt argues that Kant paved the way for existentialism. She writes:
“Kant… proved that in any proposition that makes a statement about reality, we reach beyond the concept (the essentia) of any given thing…. [he] destroyed the old identity of being and thought and, along with it, the idea of a pre-established harmony between [us] and the world” [6].
What exactly did Kant do? To see Arendt’s point, we need to understand some of Kant’s philosophy from his book Critique of Pure Reason (1781). Whole libraries have been written on it, but I want to focus on one central idea: the transcendental apperception—Kant’s “I think,” which is not a Cartesian substance but rather the unifying function that makes experience possible. “Transcendental” here doesn’t mean mystical; it simply refers to what must already be in place for thinking to happen at all. In other words, experience presupposes a single, unified point of view. Apperception is transcendental because it is the structural condition that makes any experience mine.
Kant begins with how we make judgments about the world—statements like “the sun will rise tomorrow” or “bachelors are unmarried men.” He distinguishes analytic from synthetic judgments. Analytic judgments are true by definition: the predicate is already contained in the subject. Take for example: “A triangle has three sides.” The truth of this judgment can be known simply by examining the concept. Kant says analytic judgments “clarify” because they draw out what is already implicit.
Synthetic judgments, by contrast, add something new. Their predicates are not contained in the subject concept, and their truth depends on how things actually are. “The ball is red.” “The sun will rise tomorrow.” These require experience. They are ampliative—they extend our knowledge beyond mere definitions.
So far, so good. But how do we make any judgment at all? Here Kant introduces his account of cognition. Our experience of the world involves representations of objects. The mind has two cooperating capacities: sensibility, which receives appearances, and understanding, which organizes them into concepts. Sensibility gives us the raw material of experience through the a priori forms of intuition—space and time. Understanding then synthesizes this material under its concepts. This automatic cooperation allows us to make judgments and, ultimately, to have knowledge of objects. As Kant famously put it:
“Without sensibility no object would be given to us, and without understanding none would be thought. Thoughts without content are empty, intuitions without concepts are blind” [7].
Now here’s the catch. Kant argues that we cannot perceive or know reality as it is in itself. What we encounter are appearances, and our minds must actively organize these appearances through the forms of intuition and the categories of understanding. In doing so, we constitute objects of experience—not by creating things, but by synthesizing the raw, unordered givenness of intuition into something that can appear as an object for us.
A quick example from physics makes this clearer. We never observe quantum particles as they are in themselves. What we register in experiments using massive particle accelerators are ionization tracks, scintillations, and other measurable traces. From these phenomena we infer the object ‘particle,’ but the particle as it is in itself remains beyond the limits of possible perception.
Kant’s point is that all experience works this way. We never encounter reality independent of our representations; we encounter objects only as they are structured by space and time and unified under the categories. And this entire synthesis is held together by the transcendental apperception—the unifying function that binds our representations into a single, coherent experience.
This is the break in the unity of thought and being. Kant “shatters” the ancient unity by arguing that things‑in‑themselves (noumena) are unknowable. All we can know are the representations that appear to us (phenomena). Importantly, Kant is not a pure idealist. He isn’t saying we create reality or that nothing exists outside consciousness. He’s saying that what we know is always mediated by the structures of our own minds.
This shift has far‑reaching consequences. By distinguishing analytic from synthetic judgments, Kant shows why “existence” cannot be treated as a predicate. Not only are various ontological arguments for the existence of God at risk but so too is the idea of a Cartesian immaterial soul.
Cartesian Dualism
Before the modern era, the soul was understood as an immaterial substance—Plato’s immortal soul, Aristotle’s form of the body, the Christian anima that inhabits and survives the body. René Descartes radicalized this tradition. He argued that the soul is a simple thinking substance with no extension in space, while the body is extended and material. He struggled to explain how an immaterial mind could causally interact with a physical body, but Cartesian dualism stuck.
And it stuck hard. Today it is common to assume that consciousness (not the soul) is what survives the death of the body. In the Meditations, Descartes arrives at this view by way of the famous cogito. From “I think,” he concludes that he is a “thinking thing,” a substance whose essence is to doubt, understand, affirm, deny, will, refuse, imagine, and perceive:
“All things being maturely and carefully considered, that this proposition I am, I exist, is necessarily true each time it is expressed by me, or conceived in my mind…. But what, then, am I? A thinking thing…” [8].
He then argues that bodies are not known by the senses or imagination but “by the intellect alone,” and that nothing is more clearly apprehended than his own mind [9]. The mind becomes the core essence of the person—the soul as a real, immaterial substance.
Kant dismantles the Cartesian soul by showing that it rests on a confusion between analytic and synthetic judgments. For example, suppose I tell Kant I have a perfect unicorn in my mind’s eye. Because it is perfect, I say, it must exist; otherwise it would be less than perfect. Kant replies:
“I ask you: is the proposition, This or that thing… exists—is this proposition analytic or synthetic? If it is the former, then with existence you add nothing to your thought of the thing…. If you concede, on the contrary… that every existential proposition is synthetic, then how would you assert that the predicate of existence may not be cancelled without contradiction?” [10].
In other words, I’ve smuggled “existence” into the concept of my unicorn and treated it as a necessary property. But existence is never a predicate. It adds nothing to the concept itself. A triangle has three sides—that’s analytic. But a large red rubber ball? That’s synthetic. Its existence is contingent; there is no contradiction in imagining it gone. Confusing these two kinds of judgments is the oldest trap of metaphysics.
Kant calls this mistake a paralogism [11]. The first paralogism targets the Cartesian claim that the soul is an enduring substance. The error begins with the pure concept of the soul—the “I think” that must be able to accompany all my representations—and then illegitimately projects this concept outward as a necessarily existing thing. Kant warns how seductive this move is:
“There is indeed something seductive in our pure concepts of the understanding which tempts us to a transcendent use—a use which transcends all possible experience…” [12].
But pure concepts alone can never yield objects; without intuition they remain empty. As he puts it:
“The senses furnish… only the schema for their use, and the object conformable to it occurs only in experience… [Pure concepts] can do nothing but merely determine the logical form of the judgment with regard to given intuitions” [13].
Applied to the soul, the point is simple: the Cartesian “I think” began as a structural condition of experience, but metaphysicians added predicates—simple, immaterial, enduring, existent—and treated the result as a real substance. This is what Kant means when he says “thoughts without content are empty.” I can think of my consciousness as a substance just as easily as I can think of a unicorn as grazing in a meadow. But neither thought gives me an object of experience. The same logic undercuts rational proofs of God. “Pure reason,” Kant writes, “does not in its ideas point to particular objects which lie beyond the field of experience” [14].
And this brings us back to Arendt. Kant’s critique destroys speculative metaphysics and accelerates the secular turn that follows. Before Kant, philosophers assumed that thought and being were bound together—that the soul, as an immaterial substance, gave us access to God and to the rational structure of the world. Like my perfect unicorn, God’s existence was thought to follow from the very idea of a perfect being. Kant’s transcendental idealism severs that link. It shows that we have no direct access to reality itself. God, the immortal soul, and other rational ideas become “mere speculations” of pure reason.
To be clear, Kant is not a materialist or an atheist. He isn’t denying the existence of God or the soul. He is saying that we cannot know them. All we can know are the objects given to us in experience. As Arendt puts it, Kant showed that we “reach beyond the concept” whenever we try to make claims about reality itself [15]. If Kant limits our knowledge, Kierkegaard will ask what we do within those limits.
Kierkegaard
Kant’s destruction of the rational world order ushers in a new existential condition based on individual subjectivity. Hegel tried to restore the unity that Kant had fractured. He believed that reason, history, and reality formed a single intelligible process, and his dialectic was meant to show how every contradiction is ultimately reconciled within a larger whole. In this vision, a “world spirit” (Weltgeist) progresses over time toward perfect self‑consciousness. But the price of this unity is steep: the individual becomes a mere moment in a vast historical logic, absorbed into a system that leaves little room for personal freedom or concrete choice.
Søren Kierkegaard rejects this subordination. Instead, he emphasizes the individual person who must choose and act in a world that makes no inherent sense. Frederick Copleston writes that for Kierkegaard:
“…to exist means realizing oneself through free choice between alternatives, through self-commitment. To exist, therefore, means becoming more and more an individual and less and less a mere member of a group…. Hegelianism, in Kierkegaard’s opinion, had no place for the existing individual: it could only universalize [people] in a fantastic manner” [16].
Abraham from Genesis 22 serves as his example of an authentic person and the father of faith. In Fear and Trembling, Kierkegaard points out that Abraham has no logic, no rational thought, no hedging his bets as to whether he can get out of God’s divine commandment. He is commanded to plunge the knife into his son Isaac. All he has after the three-day journey to Mount Moriah is an “infinite resignation” based purely in faith. The paradox is that Abraham must choose to suspend the moral law in order to obey the divine law. This “leap of faith” is lost, Kierkegaard argues, when people seek to avoid faith. Faith is difficult. It’s tempting to seek solace in ethics, logical proofs, metaphysics, or theodicies. But for Kierkegaard faith is already the highest movement. You stumble the moment you try to go beyond or around it:
“Would it not be best all the same to stop with faith, and is it not disturbing that everyone wants to go further? When people nowadays—as in fact variously announced—will not stop with love, where is it they are going? To worldly wisdom, petty calculation, to paltriness and misery, to all that can put man’s divine origin in doubt? Would it not be better to remain standing at faith, and for the one who stands there to take care not to fall? For the movement of faith must be made continually on the strength of the absurd” [17].
The “absurd” is a paradox because faith means fealty to God in the absence of reason or ethics. The leap is a choice to commit oneself to faith despite this absurdity. For Kierkegaard, faith is ungrounded from a factual point of view. All we have is the mystery of belief without evidence, without certainty, and without knowledge of God or the moral order. In this way existentialism begins to grapple with the repercussions of the Kantian world. If the noumenal realm is forever beyond our grasp, and knowledge is limited to phenomena, the ground shifts inevitably from metaphysical certainty to individual choice. This is why existentialism places such an emphasis on freedom.
The Problem of Evil
Modernity in general (and the Enlightenment in particular) led to an explosion of secularism with a new emphasis on science, liberty, and reason against unbending Scholastic dogmatism and religious authority. Questions previously censored were now openly discussed. So it was only a matter of time before the problem of evil resurfaced. Pain and suffering were easy to understand in the ancient order. Bad things happened to good people because the gods fought with each other and their struggles spilled over into mortal affairs. Maybe the unclean leper failed to make the appropriate sacrifices to the right god or goddess. Or maybe he was just in the wrong place at the wrong time.
But with a single deity, who is believed to be both omniscient and omnipotent, there is a problem. Why does God allow so much evil and misery in the world? Previous rational theodicies explained evil away by a vast network of interconnected higher-order goods and lower-order evils that eventually canceled each other out. By the 19th century these attempts seemed, not just tone-deaf, but an insult to our intelligence. Dostoevsky has his character Ivan reject the divine plan altogether. As he explains to his younger brother Alyosha:
“Listen: if everyone must suffer, in order to buy eternal harmony with their suffering, pray tell me what have children got to do with it? It’s quite incomprehensible why they should have to suffer, and why they should buy harmony with their suffering. Why do they get thrown on the pile, to manure someone’s future harmony with themselves? I understand solidarity in sin among men; solidarity in retribution I also understand; but what solidarity in sin do little children have? And if it is really true that they too, are in solidarity with their fathers in all the fathers’ evildoings, that truth certainly is not of this world and is incomprehensible to me” [18].
Ivan privileges his morality against a theological idea of sin that makes no sense to him. He returns his “ticket” to the afterlife:
“They have put too high a price on harmony; we can’t afford to pay so much for admission. And therefore I hasten to return my ticket. And it is my duty, if only as an honest man, to return it as far ahead of time as possible. Which is what I am doing. It’s not that I don’t accept God, Alyosha, I just most respectfully return him the ticket” [19].
As secularism flourished the gulf between us and God continued to widen. By the late nineteenth-century, Nietzsche had his “madman” declare that God was dead, which was a dramatic way of saying that the old ideas of meaning and faith had now completely collapsed. It wasn’t that God seemed to have retreated “up there,” occasionally answering prayers, and silently keeping track of us on a moral score board. It was that God seemed to be completely absent from the concerns of daily life. The divine plan eroded bit by bit until it was gone. Its meaning had evaporated. This erosion of meaning deepened during and after two horrific world wars, shattering whatever remained of the old metaphysical certainties. Out of the rubble, existentialism emerged.
The Rise of Existentialism
Once Kant shattered the unity of thought and being we could no longer count on a rational world for meaning and purpose. In the absence of meaning that is given to us we are forced to create it for ourselves. Thus, existentialism begins with the idea that our life has no inherent purpose. That life largely makes no sense and has no clear meaning. We lack a roadmap as it were and are left on our own as subjective beings to decide what to do with ourselves.
Although both rejected the label, Karl Jaspers and Martin Heidegger mark the beginning of 20th century German existentialism. Jaspers called the background horizon of our everyday existence the Encompassing (das Umgriefende). In certain moments—death, anxiety, guilt, or some other crises—our ordinary modes of understanding collapse. These are “boundary situations,” the moments during which the horizon becomes visible and we glimpse our own vulnerability. The Encompassing is always what we already are, but boundary situations jolt us into recognizing it. The self-reflection they provoke can open the possibility of a more authentic mode of existence.
Heidegger’s Being and Time owes a huge unpaid debt to Kierkegaard, especially in its exploration of anxiety and authenticity. For both thinkers, anxiety is not a psychological disturbance but a disclosure: it strips away our everyday distractions and confronts us with the fact that we are “thrown” into a world we did not choose. Kierkegaard captured this temporal tension in the line from his journals, “Life can only be understood backwards; but it must be lived forwards.” Heidegger radicalizes this insight by arguing that our being is structured through time itself: we exist as beings oriented toward possibilities, projecting ourselves into an uncertain future even as we interpret ourselves from what has already been. For Heidegger, our being is time.
French existentialism was popularized by Jean‑Paul Sartre and Albert Camus. Sartre famously wrote that “existence precedes essence,” the idea that we are thrown unceremoniously into the world and must become who we are through the choices we make. Even choices made inauthentically, in “bad faith,” remain our own. And not to choose is still a choice. We discover ourselves only by living and choosing as best we can. Camus, however, approached the human condition from a different angle. For him, the fundamental fact is “the absurd,” the mismatch between our hunger for meaning and a world that offers none. Confronted with this tension, we can either collapse into nihilism or resist it by creating meaning through our actions. For Camus, rebellion—not certainty—is what allows us to live meaningfully in an indifferent world.
Almost as soon as post-war existentialism took shape it began to fall apart. Sartre sought to synthesize existentialism with Marxism while Camus was a strong opponent of totalitarianism. This led to a public feud between the two that was never resolved. Sadly, Jaspers’ ideas never really took hold. Heidegger’s career was in tatters as he went through the post-war denazification process. After he was cleared in 1949 he shifted toward mysticism and poetry, arguing that the Being of beings is “the nothing” (das Nichts) that “nihilates” beings by stripping them of significance.
By the mid-twentieth century consumerism exploded. During the Depression money was scarce. Then the war had enforced rationing and austerity measures. For the first time in years pent-up demand was let loose and people had discretionary income. “Buy now, pay later” became the new trend. Everything from kitchen appliances, washing machines, cars, Barbie dolls, Hula Hoops, poodle skirts, and a thousand other new products were hitting retail shelves. Jazz got hotter and the new rock n’ roll music took everyone by storm. A wave of optimism and relief took hold in the Western world. Existentialism’s emphasis on angst, choice, and authentic meaning seemed irrelevant. These concerns didn’t so much die as just fade away in the wake of improved standards of living. And yet our restlessness never went away. We just couldn’t buy enough stuff to drown out the old voices of anxiety. This lingering unease is all around us today. But that story will have to wait for a future blog post.
Footnotes
[1] Kirk, G.S. and Raven, J.E. The Presocratic Philosophers. Cambridge: Cambridge University Press. 1957, p. 269.
[2] Aristotle. Metaphysics XII. Hugh Tredennick, Trans. Loeb Classical Library. Cambridge and London: Harvard University Press. 1935. Reprinted: 1997, 1072b20-22.
[3] Aquinas, Thomas. Summa Theologica. Q.16 A.3. Online at https://www.newadvent.org/summa/
[4] Kant, Immanuel. Critique of Pure Reason. Paul Guyer and Allen W. Wood (Eds). Cambridge: Cambridge University Press. 1998, B xvi.
[5] Matthew 8:20/Luke 9:58.
[6] Arendt, Hannah. “What Is Existential Philosophy?” Essays in Understanding. Jerome Kohn (Editor). New York: Schocken Books. 1948, p. 168.
[7] Kant, Immanuel. Critique of Pure Reason. Paul Guyer and Allen W. Wood (Eds). Cambridge: Cambridge University Press. 1998. A51/B75.
[8] Popkin, Richard H. The Philosophy of the 16th and 17th Centuries. New York: The Free Press. 1966, pp. 134–137.
[9] Popkin, p. 141.
[10] Critique, A598/B626.
[11] Critique, A354/B399.
[12] Kant, Immanuel. Prolegomena to Any Future Metaphysics. 2nd Edition. James W. Ellington (Trans.). Indianapolis: Hackett Publishing Company. 2001. 33.
[13] Prolegomena, 34.
[14] Prolegomena, 44.
[15] Arendt, p. 168.
[16] Copleston, Frederick, S.J. A History of Philosophy. Vol. 7. New York: Paulist Press. 1963, pp. 335-336.
[17] Kierkegaard, Søren. Fear and Trembling. Alastair Hannay (Trans.). New York: Penguin. 1985, pp. 40-41.
[18] Dostoevsky, Fyodor. Brothers Karamozov. Richard Peaver and Larissa Volokhonsky (Trans.). New York: Farrar, Straus, and Giroux. 1990, p. 244.
[19] Dostoevsky, p. 245.