William Ewart Gladstone was Britain’s prime minister four times between 1868 and 1894, a member of Parliament for more than sixty years, a brilliant and passionate orator, an accomplished writer, and an indefatigable social reformer. Lord Kilbracken, his private secretary, estimated that if a figure of 100 could represent the energy of an ordinary man and 200 that of an exceptional one, Gladstone’s energy would be represented by a figure of at least 1,000.

That’s some multiple. But then I vividly remember the day a Benedictine monk walked into my high school classroom and told us, “Some people are more alive than others. Even permanently so.” I find that true to my own experience, even if it is hard to state clearly in what form such vitality exists.

There are over a dozen common forms of energy, as usually itemized, from chemical, gravitational, and electromagnetic to nuclear, thermal, and wind. It is a formidable register—but human energy rarely appears in such listings. When set against those other categories, what do we mean by the term, anyway? The word energy itself comes from the ancient Greek ἐνέργεια, meaning “activity.” Aristotle said it was a condition that describes the capacity to do work. More recently, human energy has been similarly defined as the amount of stamina, vigor, or “juice” a person has to engage in a particular activity. None of this, unfortunately, takes us very far. There is obviously a difference between a person full of gusto and joie de vivre and a person with significant actual productivity. Marcel Proust spent much of his adult life lying in bed, but his masterwork, À la recherche du temps perdu, has 1,267,069 words in it, double the number in War and Peace. Voltaire spent eighteen hours a day writing or dictating to secretaries, eventually completing an output covering two thousand works; he sustained himself by drinking, so it was said, fifty cups of coffee a day. But while such prodigious feats are all about get-up-and-go, it is not something, a chemical reaction, but someone who has to do the getting up and going.

In November 2021, The New Yorker published an entertaining article by staff writer Nick Paumgarten, “What a Feeling,” retitled for the internet “Energy, and How to Get It.” Each of us, he explains, has many trillions of mitochondria, “the organelles that fuel living creatures: the powerhouses of the cell, as every schoolkid learns.” They convert glucose and oxygen into adenosine triphosphate, or ATP, “the primary cellular fuel.” These mitochondria transform chemical energy into electrical energy. If a cell were a car, mitochondria would be its engine.

However, Paumgarten acknowledges that the human variety is a case apart: “Energy is both biochemical and psychophysical, vaguely delineated, widely misunderstood, elusive as grace.” After granting that the word “is a misnomer, or at least an elision,” he recognizes that, while energy has to do with vigor, it also embraces “charisma, aura, and temperament.” Further, there is a distinction to be made between calorific energy and levels of cortisol, a hormone that is released in response to stress—in other words, chemical energy potential in the body compared with hormones that influence mental energy. Plainly, energy goes beyond chemical interaction—its outcome elusive as grace, indeed.

So, can we say—outside a chemical reaction—­what human energy is? For centuries, we have been trying to answer that question. It was of particular interest to late-nineteenth and early-twentieth-century philosophers. Schopenhauer wrote about man’s “will to live,” Freud of the libido being energy’s vital source, while in 1907, in his book Creative Evolution, the French philosopher Henri Bergson identified an élan vital that impelled consciousness and evolution. This notion also corresponds to the German word Lebensdrang, which translates as “life-urge.” Most languages have their own terms for it: Scottish Gaelic has two, lùth (“energy”) and *beòthachd *(“vigor”); Mandarin Chinese three, lìliàng (“strength”), *néngyuán *(“power”), and *jīnglì *(energies in the plural); and Hindi at least four, covering energy systems, consumption, sources, and supply. Interesting, but still not that helpful.

What, for instance, happens when one deploys mental energy to overcome deficiencies in other forms of ἐνέργεια? John Hersey, in “Tattoo Number 107,907,” included in the 1963 story collection Here to Stay, writes at length about a concentration-camp survivor from the Second World War, a young Berlin intellectual named Alfred Stirner. Arriving in Ausch­witz after being herded from camp to brutal camp, Stirner begins to work at growing stronger. “He had learned that men in a concentration camp survived on a margin of a very few calories of surplus energy each day, and that there were certain tricks for hoarding one’s inner warmth.”

Stirner knows he must grasp every chance to relax. Five seconds of rest in every minute means five minutes of rest in every hour. He asks permission to go to the latrine as often as possible without arousing suspicion and tries to spend the maximum time there: “to excuse himself, furthermore, when several others had already gone, because then he would have to wait, at ease, for a free pit.”

Fire destroys that which feeds it.

—Simone Weil, 1940

Even the act of tearing bread at breakfast is a waste of energy, so he sharpens one edge of his spoon—his one personal possession, kept in a single pocket on his trouser leg—so he can cut chunks more easily. Among other ruses, he realizes the psychological importance of cleanliness, and once a week, when inmates were allowed to be shaved—by camp barbers, with cold water and dull blades—he always turns up, no matter how tired. On May 3, 1945, during a death march, he walks into a forest clearing to be greeted by an American soldier. He has come through.

Stirner’s conservation strategies still deploy energy, mainly by using his brain. In fact, some 20 percent of our energy is expended by that organ. (In young children the amount is nearer to 50 percent.) But Stirner’s ability to survive is not just a mental act; it also requires tenacity and strength of will.

What about the animal kingdom at large? Do dogs, foxes, horses, and chimpanzees use energy in this compound way? In Rogue Heroes, Ben Macintyre’s compelling history of the Special Air Service in the Second World War, a unit marauding behind enemy lines in the Libyan Desert reaches an ancient storage tank hollowed out of rock. It is not empty: “In one corner lay the parchment-dry, skin-covered skeleton of a desert fox that must have fallen into the old well and found it impossible to escape.” One man, a battle-hardened commando, confides to his diary: “It made quite an impression on me. It would obviously carry on, until it was too weak to jump any more. I felt deepest sympathy for the animal. The desire to live. The desire to see things through.”

The fox’s reaction to his predicament may seem no more than an innate impulse, but nonhuman animals employ energy not just out of instinct (here, the imperative to survive); they have character, and that drives their will to action. To take just one example among many: Each winter for nearly twenty years, Michael Fishbach, the executive director of the Great Whale Conservancy, has traveled to the Gulf of California, off Mexico’s west coast, to study blue and humpback whales. In 2011, he and his team spotted a humpback trapped in a fishing net and spent an hour freeing it. Afterward, in an hour-long display of apparent gratitude, the whale swam near their boat, leaping into the air about forty times. What the whale was feeling—maybe simply high spirits—dictated its use of energy.

To return to the world of humans: Napoleon, Dickens, Humboldt, and Goethe (compared with Voltaire, a pitiful 143 volumes) in their output outshone Gladstone, but it wasn’t just physical stamina that made them do so, but a compound of the physical, the intellectual, and the spiritual—­or, to put it differently, their characters and will. As Samuel Smiles, author of the best-selling Self-Help (1859), described this synthesis: “It is energy—the central element of which is will—that produces the miracles of enthusiasm in all ages. Everywhere it is the mainspring of what is called force of character, and the sustaining power of all great action.”

And such powers can take extraordinary forms. People perform superhuman feats when threatened—such as the climber in Utah who, pinned by an eight-hundred-pound boulder, amputated his own arm, a procedure that required little physical effort but an enormous amount of mental energy. Chillingly, eighteenth-­century Rhineland gentry would, as an enrichment to fox hunting, ride after Roma, but according to one story the women, on hearing “the music of the pack,” would throw themselves to the ground in a fetal position, spoiling the chase. The huntsmen soon hit on a solution: they tied their babies to them, and in panic the mothers found the energy to flee.

Then there is what, for want of a better word, I would describe as the spiritual element, as embodied in Samuel Taylor Coleridge’s comment that “the act of praying is the very highest energy of which the human mind is capable; praying, that is, with the total concentration of the faculties.” Such an engagement was further developed in the late 1950s by the Indian guru Maharishi Mahesh Yogi, whose Transcendental Meditation techniques emphasized how intense concentration could release bodily energies and higher states of consciousness.

A similar emotional engagement is explored by the French sociologist Émile Durkheim, who in The Elementary Forms of Religious Life (1912) argued that people in certain religious groupings can become “delirious” or “ecstatic,” capable of releasing energies far beyond the norm. This is an extension of what Coleridge was describing—­the release of a supreme amount of energy—and it derives from sharing with others in the same endeavor. “Every collective representation is in a sense delirious,” Durkheim says. “Religious beliefs are only one particular case of a very general law.” What a congregation united in its religious fervor may experience is mirrored in what a service­man may exhibit in the heat of battle: “We know what the flag is for the soldier; in itself, it is only a piece of cloth,” but it can release exceptional powers, far beyond what that soldier might be capable of in peacetime. And Durkheim’s examples of the religious zealot and the fighting man can be variously extended—the energy created simply by being different, for instance: Jews, Jains, Pharisees.

My friend the scriptwriter William Nicholson (Shadowlands,* Gladiator*, Les Misérables) has an interesting take on this: “There are endless examples of people in very poor physical and mental condition who nevertheless achieve immense outputs. Rather, our energies often come from a combination of neurotic drive and positive response. The drivers are all familiar: making up for psychic wounds from parents or peers, suffering from class disadvantage, being small, being ugly, being poor—all the factors that can make a person determined to show the world that they’ve been underestimated—in short, the need to achieve.”

Bill is himself the director of two feature films and the author of some sixty film scripts, sixteen novels, at least five stage plays, and several TV documentaries; he gets up at five every morning. Though challenges can spur one to action, Bill explains, such a response is not universal: “Not everyone who is disadvantaged turns their wounds into arrows. All too many sink into self-contempt and depression. This is where the positive response comes in. Energy requires feedback: you need to discover that when you put out the energy you get a reward.”

This is to put a mainly positive spin on how we define human energy, but we also need to view it from a negative aspect, hence Nietzsche’s observation that “reckoned physio­logically,” a feeling of ugliness can diminish man’s output too: “It recalls decay, danger, impotence; he actually suffers a loss of energy in its presence…His feeling of power, his will to power, his courage, his pride—they decline with the ugly, they increase with the beautiful.”

Such thinking can take one down dangerous paths, but Nietzsche usefully points out that one can lose energy in a way that bypasses the chemical, such as getting dejected. Indeed, one does not even have to be feeling depressed to suffer lethargy of spirit. As long ago as the eleventh century, a doctor known as Constantine the African advised patients to harbor their energies: “You must avoid and reject heavy burdens and cares because excessive worrying dries out our bodies, leaches out our vital energies, fostering despair in our minds and sucking out the substance from our bones.”

Ashwatthama shooting cosmic fire at the Pandavas, miniature from a c. 1616 Persian edition of the Mahabharata. The Metropolitan Museum of Art, Rogers Fund, 1955.

Around 1978, the Anglo-Russian intellectual Isaiah Berlin, stung by criticism that he had never written a magisterial work, set out to write a major study of German Romanticism. For several years, postgraduate students engaged in their own research at the British Library were acutely aware of a stately European gentleman in a beautiful three-piece suit totally engrossed in his explorations in the North Library, surrounded by a mass of books, all of which he diligently read through one by one. But then he faltered, and no great work came. Inspiration and vision are forms of energy, and Berlin’s project came to a standstill because he lacked these. He was, for all his capacities, incapable of a volume of grand synthesis.

In the modern idiom, Berlin was “burned out”—although in her essay “It’s Just Too Much,” retitled “Burnout: Modern Affliction or Human Condition?” for The New Yorker’s website, the Harvard historian and journalist Jill Lepore finds fault with the word as a psycho­logical term synonymous with depression: “To question burnout isn’t to deny the scale of suffering, or the many ravages of the pandemic: despair, bitterness, fatigue, boredom, loneliness, alienation, and grief…Burnout is a metaphor disguised as a diagnosis.” (Donald Trump, who, once his college days were over, swore off any physical exercise outside leisurely golf, believes that we all have a finite amount of energy, like an unrenewable battery, and exercise only depletes this limited store.) But it is a popular diagnosis all the same; just last year, the English translation of French historian Georges Vigarello’s 2018 study A History of Fatigue was published.

If one looks back in time, use of the word burnout for a medical condition emerged in the 1970s, when clinicians borrowed a term previously used to describe catastrophic building fires and depleted fuel resources. Burnout is not the first work-related infirmity to take on meaning from the industrial city: exhaustion, propelled in part by its association with steam-engine emissions, first became a pressing medical concern in the middle of the nineteenth century, when it was considered a symptom of the effects of industrialization and the pressures of urban life. Throughout the nineteenth century, as Cara New Daggett explains in her book The Birth of Energy, work became increasingly understood through energy-based metaphors. This association was catalyzed by the “discovery” of energy itself in the 1840s by a group of British scientists and engineers who used steam-engine experiments to develop the laws of thermodynamics. As Daggett tells it, the fledgling field of energy science, which paved the way for future industrial landscapes, quickly migrated from examining steam engines to looking at the workers who operated them. Energy management led to a growing emphasis on handling workers, and these breakthroughs sparked a simultaneous revolution in neurology, whose practitioners discovered in the 1840s that the nervous system was powered by electricity. That was when nerves were first likened to electrical wires, the brain to a battery. However, in the course of these evolutions, the issue of human energy was almost forgotten.

In Tom Stoppard’s play about consciousness, The Hard Problem, Hilary, the protagonist, is a youthful research psychologist. “Who’s the you outside your brain? Where?” she questions. “The mind is extra…We’re dealing in mind-stuff that doesn’t show up in a [brain] scan—accountability, duty, free will, language, all the stuff that makes behavior unpredictable.” For her, a computer that plays chess can be conscious only if it “minds losing.” Intellect and personality are theoretically explainable by chemistry and related sciences, but they haven’t been yet (despite the recent excitement over Anil Seth’s book Being You), and once one accepts that qualities of character are part of the makeup of human energy, one can go further and ask whether there is an ethical component to those trillions of mitochondria.

That may seem fanciful, and one’s efforts may be devoted to destruction or perseverance or simply brushing one’s teeth—a waiter or waitress facing an eight-hour workday in a coffee shop requires stamina simply to make it through to the end of the working day. One can be preoccupied by the doers of great deeds or creative acts, but endurance can have just as much worth as creativity.

And yet, how energy is used at its most notable suggests something more, a moral dimension, and that element isn’t just an add-on but is part and parcel of what constitutes human energy. Back in 1906, the philosopher and psychologist William James titled his Presidential Address to the American Philosophical Association “The Energies of Men.” Ethics, he argued, was not about values or principles but about the organization of energy in the service of personal, aesthetic ideals. He was not merely cashing in on the then popular use of the term. (He is credited with popularizing, in 1891, a special word for overwork, with its continual rush and tension: Americanitis.) James was asserting that energy was not a metaphysical phenomenon but rather an activity—­living itself—and the task of ethics was therefore not to prescribe the features of some universal good but to organize the energies of life in service to one’s own personal demands, namely, against “limits on the full and free expression of human life,” in the words of the scholar Sergio Franzese. For James, Franzese writes, “the ethics of energy does not set moral aims and values” but rather “it is…the way in which one becomes the master and author of one’s own energy.”

I imagine that one of the first forms of behavior, like one of the first signals, may be reduced to this: “Keep me warm.”

—Michel Serres, 1982

In this argument, human energy, fully defined, recalls a maxim attributed to W.B. Yeats: “Every conquering temptation represents a new fund of moral energy. Every trial endured and weathered in the right spirit makes a soul nobler and stronger than it was before.” Even Gladstone, working innocently to save women of the night, might have agreed with that.

Human energy is unique among the energies of the universe, so no wonder it exerts such fascination—for me, at any rate. The Benedictine monk whose insight into being alive so inspired me in my teens was one Dom Aelred Watkin. He taught medieval history and would sometimes allude darkly to having had an affair in his youth with the British actress Deborah Kerr. He would illustrate how to take deeply unconnected objects—say, a mandolin, a horse’s bridle, and an old Egyptian coin—and write a convincing essay combining all three. A favorite quotation of his was from William Blake: “Everything that lives is holy; life delights in life.” He wrote several books, notably The Enemies of Love, went on to become headmaster of my school, then took charge of a parish in a market town in southeast England, where he was promptly elected mayor. He was also made titular abbot of Glastonbury, 270 miles away. He died in his eightieth year, in 1997, having lived the fullest of lives. How better to employ human energy?