To the question implicit in all of Søren Kierkegaard’s writings—how can one be a human being in the world?—one is tempted to respond: by not being Søren Kierkegaard. The degree to which the Danish philosopher sought out suffering borders on the masochistic. Indeed, if asked what it means to be a Christian, he might have replied: to suffer monstrously. Shortly before his death in 1855 at the age of just 42, he wrote that “being a Christian is the most frightful of all agonies, it is—and so must it be—to have one’s hell here on earth.” The titles of his many books——Fear and Trembling, The Sickness unto Death, The Concept of Anxiety—certainly bear out this claim, as did his life, which was marked by suffering almost from start to finish.

Born in 1813, the year of the Danish state bankruptcy, Kierkegaard was one of just two siblings—there were seven children in all—to live past the age of 33. In 1840, he proposed marriage to Regine Olsen only to break off the engagement a year later, a sacrifice he believed his destiny as an author demanded. For the next 14 years he lived alone, writing at an inhuman pace his frail body could hardly endure, getting drawn into frequent controversies with tabloid newspapers or the Danish church that made him an exile in his own country, as his biographer Joakim Garff put it.

Yet he persisted in the almost Christ-like belief that his suffering would benefit humankind. “I want to make people aware so that they don’t waste their lives and fritter them away,” he wrote in 1847. In The Sickness Unto Death (1849) he warned that losing oneself “can pass off in the world as quietly as if it were nothing; every other loss, an arm, a leg, five dollars, a wife, etc., is bound to be noticed.” This danger was an especially modern danger. Rapid industrialization, the rise of the masses, and the materialism of capitalist economies were all developments that threatened the psychology of the individual human being, Kierkegaard believed. In Concluding Unscientific Postscript (1846), he wrote: “The abstract leveling process, that self-combustion of the human race, produced by the friction which arises when the individual ceases to exist as singled out by religion, is bound to continue, like a trade wind, and consume everything.”

As Clare Carlisle shows in her extraordinary new biography, Philosopher of the Heart, Kierkegaard was “perhaps the first great philosopher to attend to the experience of living in a recognizably modern world of newspapers, trains, window-shopping, amusement parks, and great stores of knowledge and information. Although life was becoming materially easier and more comfortable for affluent people like himself, it also provoked new anxieties about who to be and how to appear.” In other words, he lived the very modern life whose ambiguities, contradictions, and difficulties he explored in his writing. He despised the rise of mass society yet spent his entire life living in central Copenhagen; he wrote with scorn of the bourgeoisie yet lived in the wealth and comfort provided by his father’s inheritance; he was a passionate Christian who made himself the most vocal antagonist of established Christianity. What’s more, Kierkegaard explored the modern condition not as a preacher or lecturer or institutionally backed academic; he wrote “without authority,” as he himself put it. “Kierkegaard saw the entire academic enterprise as an evasive flight from actual existence,” Carlisle observes. “He connected this intellectual detachment with a cynical commercialization of knowledge: professors in the modern universities traded ideas as merchants traded commodities—but more duplicitously, for their smartly packaged abstractions contained no genuine wisdom.”

For Kierkegaard, the spiritual crisis of humankind demanded the opposite of this kind of arrogant detachment. The threat to the modern self was too great. To be constantly surrounded by people, absorbed not by their relationship to God but to the secular clatter of bourgeois society, was to risk losing one’s grasp on selfhood. He believed the self was a synthesis between the finite and the infinite, between the temporal and the eternal, always in the process of becoming, always changing. This made it vulnerable to loss, solipsism, disintegration—in short, to the severance of its relationship to God, which he considered the most important aspect of authentic selfhood. He maintained that every life that is “not grounded transparently in God,” no matter how full and happy, is a life lived in despair, since despair is the “loss of the eternal and oneself.” The task of the individual, then, is to have faith, which is the opposite of despair: “in relating to itself and in wanting to be itself, the self is grounded transparently in the power that established it.”

Kierkegaard knew whereof he spoke. His massive oeuvre can be read as one long, compulsive, maddening attempt to understand who he was and where in the world he belonged. As Carlisle observes, he was “caught in a dialectic between worldly achievement and aesthetic renunciation”; between the desire to continue writing and the temptation to retire to some rural parish and give up his authorship. In this respect Kierkegaard’s life, like Nietzsche’s, was a one-man show, a monodrama to which contemporary audiences responded with bewilderment. No one really knew what to make of his works. When the two volumes of Either/Or appeared in Copenhagen in 1843, Signe Læssøe wrote to Hans Christian Andersen, who was in Paris at the time: “I only understand a small fraction of the book; it is altogether too philosophical.”

With his many pseudonyms, his penchant for irony, and his blending of literary and philosophical genres, Kierkegaard invited such responses. Nothing he did or wrote was ever straightforward. “Paradox,” he wrote in his journal in 1838, “is the intellectual life’s authentic pathos, and just as only great souls are prone to passions, so only great thinkers are prone to what I call paradoxes, which are nothing but great thoughts still wanting completion.”

Because it is so difficult to identify any clear propositions in Kierkegaard’s writing, or to separate the trickster from the prophet, we are fortunate to have in Carlisle an extraordinarily lucid and perceptive interpreter. Densely researched yet compellingly fleet-footed, Philosopher of the Heart frames Kierkegaard’s writing as a difficult and demanding examination of what it means to be an individual human being in the tumultuous and changing world of 1840s Copenhagen. “He has discovered,” Carlisle writes, “that living in a modern metropolis intensifies an experience of anxiety that he recognizes as universally human. Ever since Adam, he believes, human beings have felt anxious—and now, caught in the city’s myriad reflections, their anxieties multiply as they become uneasy spectators of their own lives.”

As the present continuous tense in the sentence I’ve just quoted indicates, Carlisle’s book is not written from the panoptic view common to the practice of biography. Instead, she joins Kierkegaard on his journey to selfhood “and confronts its uncertainties with him.” Unfortunately, the journey is not always a smooth one. Constructions like “Last month, he left for Berlin,” or “In Works of Love, a collection of discourses on the Christian ideal of neighborly love published last year,” are more distracting than they are clever, especially since Carlisle moves back and forth in time with a restlessness of her own that makes a mess of the book’s chronology.

That said, Carlisle’s jagged approach does a far better job of any book I’ve ever read in showing us the development of Kierkegaard’s thinking, and humanizes the difficult Dane to an unprecedented degree. Her portrait is an imaginative achievement of the highest order. One is reminded that despite his polemical public persona, Kierkegaard was exceedingly kind to family and friends, especially if he found them struggling. To his sister-in-law Henriette, who suffered from depression, he wrote long, sensitive letters reminding her to “love yourself”: “When one is suffering and unable to do much for others, it is easy to fall prey to the melancholy thought that one is superfluous in the world, as others perhaps sometimes give one to understand. Then one must remember that before God every person is equally important, without reservation equally important.” Kierkegaard’s friend Hans Bröchner once said of him that “he understood as few do and he comforted not only by covering up sorrow but by first making one genuinely aware of it, by bringing it to complete clarity.”

For all his anguished faith and self-mortification, Kierkegaard remains for many an indispensable interpreter of modern selfhood. In Carlisle’s portrait, he emerges as a kind of Socrates of Christendom who put his “extraordinary literary gifts, his philosophical ingenuity, his powerful imagination” in the service of reevaluating what it means to become a Christian. The results of that reevaluation may not be especially appealing—being a Christian, he claimed, means feeling every day the unrest of the question of whether in fact one is a Christian—yet the personal journey to greater self-knowledge that he unravels along the way remains deeply stirring. Above all, it is because of his profound sensitivity to, and intimacy with, the despair and melancholy of living that he remains one of the least oppressive religious thinkers. “Compel a person to an opinion, a conviction, a belief — in all eternity, that I cannot do,” he wrote. “But one thing I can do: I can compel him to become aware.”

While writing this review, I had a conversation with my father about Kierkegaard and Carlisle’s book, which he was in the process of reading. He asked me if I thought Kierkegaard really believed, a question I rather pompously dismissed out of hand as self-evidently absurd. How could one possibly doubt that Kierkegaard, so passionately devoted to Christianity that he practically killed himself writing about it, was really a believer? And yet, in the days after our conversation, I began to think my father’s question contained a valuable insight (sorry, dad). After all, Kierkegaard’s understanding of what it means to lead a Christian life is so demanding it becomes, in practice, inhuman. “The task is not to comprehend Christianity but to comprehend that one cannot comprehend it,” he wrote in The Point of View For my Work as an Author, a remark that Albert Camus may have had in mind when he argued, in The Myth of Sisyphus, that Kierkegaard “does more than discover the absurd, he lives it … That face both tender and sneering, those pirouettes followed by a cry from the heart are the absurd spirit itself grappling with a reality beyond its comprehension.”

Where Camus determined to live in the state of the absurd, Kierkegaard made the leap to Christianity. But his version of Christianity can often seem indistinguishable from the absurd condition—indeed, as Camus argues, Kierkegaard endows God with the very attributes of the absurd: unjust, incoherent, and incomprehensible. And in his ferocious attacks on the Danish Church and established Christianity, Kierkegaard can sometimes sound like Nietzsche; like him, Kierkegaard recognized, not that God was dead, but that faith was dead in the soul of his contemporaries, and in particular of the very people who claimed to be emissaries of God. “Kierkegaard is deeply ambivalent towards Christianity, and he deploys the term ‘Christendom’ disparagingly,” Carlisle writes early on. “He believes that Christianity – its customs, its concepts, its ideals – has become so familiar, is taken so entirely for granted, that it might soon disappear beneath the horizon.”

In this way, for those of us who either cannot or refuse to make that leap, for whom Christianity has indeed disappeared beneath the horizon, Kierkegaard’s writing has the paradoxical effect of returning us to the absurd, which is to say the confrontation between our desire for meaning and the silence of the universe. And by returning us to our absurd condition, by revealing to us the impossibility and monstrosity of a Christian life, Kierkegaard, perhaps inadvertently, helps us to begin to answer the question he first set out to explore: How can one be a human being in the world?