In his book On Grand Strategy, Gaddis distils lessons from one of Yale University’s most popular courses, one he has co-facilitated for years. There is always a sizable waitlist to join this yearlong survey of primary texts from antiquity and historical case studies. By examining the lives and writings of leaders and writers from the last several millennia, Gaddis shows us how grand plans succeed and where they tend to falter.

When Xerxes and his uncle-advisor Artabanus were discussing how best to attack Athens in 480 BC, they ended up talking past each other. Xerxes saw potential for glory and expansion on the battlefield, but Artabanus saw logistical nightmares in realizing those dreams: supply chain issues, topographical challenges, transportation problems. Whether Xerxes’ Persian army really was over 1 million men as one ancient estimated, or if it was “merely” 100,000, the questions of how to feed and keep up morale were not simple ones. Xerxes listened to his uncle’s council, but in the end offered the rebuttal that “if you were to take account of everything…you wouldn’t do anything…Big things are won by big dangers.”

And so Xerxes gave his uncle managerial responsibilities over the realm already conquered, while he departed with his armies to double the size of that realm. Xerxes’ colossal army bested Sparta’s elite fighting force; they overcame major geographic hurdles, like building a bridge over a river by lashing together over 300 ships, allowing armies to march across a chasm and continue on toward Athens. In the end, however, Xerxes’ forces were soundly defeated, and he was forced to return. Should Xerxes have listened to Artabanus? Or did his advisor’s prevaricating and fretting create its own problems?

Twenty-four centuries later, an Oxford don discovered an ancient template that helped explain dilemmas like the one Xerxes and Artabanus faced. At a party in Oxfordshire, Isaiah Berlin, a Latvian, Bolshevik-fleeing Jew who emigrated with his family to England, was introduced to an aphorism from the ancient Greek poet Archilochus: “The fox knows many things, but the hedgehog knows one big thing.” The surrounding context of the phrase is no longer extant, but Berlin seized on the phrase and made it a kind of intellectual game, to discover who was a fox and who was a hedgehog. According to Berlin’s heuristic, a hedgehog has a central idea about life to which everything in life corresponds and finds significance. The fox, by contrast, pursues many things that do not obviously relate to one another, and may even conflict with one another. At that party, Berlin and other guests played a game in which they divided thinkers into hedgehogs and foxes. Nietzsche, Dostoevsky, and Plato were definitely hedgehogs, while Aristotle, Shakespeare, and Goethe were far more foxlike.

Berlin himself did not push his mammalian typology much further than an essay that questioned whether Tolstoy’s novel War and Peace revealed him to be a fox or a hedgehog. Berlin argued that Tolstoy could not make up his mind, and that the hedgehog and fox vying within him left him a tortured soul. To Berlin’s surprise and mischievous amusement, the typology became a sensation. People read the essay and sorted themselves and others; professors posed the question to students in their classes of whether this or that luminary was a hedgehog or a fox; the animals became common references in popular culture. Taking a page out of Aesop’s book, Berlin immortalized his ideas by personifying animals.

In the story of Xerxes and Artabanus, each quadruped shows up in all its idiosyncratic glory: Xerxes, the headstrong leader with the grand plan to achieve glory and expand his empire, has all the markings of a hedgehog. His advisor, Artabanus, by contrast, fits the profile of the fox, a man with a diverse knowledge base, examining a plan from every conceivable angle and vetting it for possible shortcomings.

When 20th century social scientists investigated what kinds of experts from universities, government, and media made the best predictions, they discovered that there were no statistical differences between liberals and conservatives, or between pessimists and optimists, or between any other ideological groups. The biggest difference they found was between those who identified as foxes and those who identified as hedgehogs. They discovered that foxes did far better at predicting the future. The story of Xerxes’ ignominious retreat suggests that the fox—not the hedgehog—had been right millennia ago, too.

One might be tempted to conclude that the lesson here for strategy building is to become a fox rather than a hedgehog, but the reality is that each temperament, by itself, misses something crucial. After stirring up decades of conversation and debate over the dichotomy, Berlin confessed that he was more a fox than a hedgehog himself, but that no one is just one without the other. In fact, it is easy to default toward one, but perhaps the key to a grand strategy is moving forward while holding both in tension.  

What is grand strategy? The simplest definition is “the alignment of potentially infinite aspirations with necessarily limited capabilities.” When you consider a goal, you cannot dream about it without giving thought to the means available to you: the skills, opportunities, and connections to accomplish your goal. To borrow Isaiah Berlin’s language of hedgehogs and foxes, the hedgehog focuses on unlimited ends (one big thing), and the fox focuses on limited means (many smaller things).

But as discussed earlier, the goal is not to elevate the fox over the hedgehog or vice-versa. The Persian King Xerxes had his sights set on unlimited glory, and he stopped paying attention to the means. His advisor so harped on the limitations of the means that he enervated ambition and action. They needed each other. The novelist F. Scott Fitzgerald was onto something profound when he described high intelligence as “the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function.” The hedgehog and the fox represent two contradictory ideas, and if both are not held together as we move forward, we fail to achieve goals, either because they were too lofty to be achieved, or we hedge and qualify over the means, such that we end up aiming for nothing.

History reveals the profound difficulty of toggling between hedgehog and fox, especially among leaders. The person brave enough to traverse the rickety bridge between fox and hedgehog is the brilliant strategist. It is in this vulnerable space between unlimited ends and limited means that action takes place. The struggle is learning how to connect the two, never losing sight of ambitious goals, but also remembering the particular set of limitations that one faces.

Augustine is often referred to as “Saint Augustine,” though it is unlikely he would have embraced such an honorific. If you read his Confessions, a work that virtually began the genre of autobiography, you see that he does not give himself a break. He considered himself a sinner rotten to the core since infancy. He goes on to detail a long, sordid history of sexual exploits from his youth into young adulthood. He devotes significant narrative space to a moment when he and his friends stole fruit off a pear tree—not to eat but simply for the sport of it. That pear tree has become the second most famous tree in the Judeo-Christian tradition. Confessions moves between philosophical musings and self-flagellation over the things he had done, detailing all God needed to save him from.

In contrast to his Confession, his magnum opus, The City of God Against the Pagans, is a poorly organized, gargantuan work, in which Augustine attempts to defend the Church against accusations that Christianity had set the Roman Empire’s decline in motion. One of the major tasks of his book is delineating what he calls the City of Man and the City of God, ferreting out what belongs to Caesar and what belongs to God. Augustine was grappling with grand strategy: recognizing the limitations of human capacities to apprehend and live with the infinitude of the afterlife looming in the background. Here again, we see the wrestling between limited means and infinite ends, thinking like a fox aware of complexity and necessity of the City of Man, while also remembering, like a hedgehog, the one big thing: the City of God.

How did Augustine do? Did he fit F. Scott Fitzgerald’s view of high intelligence, of being able “to hold two opposed ideas in the mind at the same time, and still retain the ability to function”? In some ways, he exemplified it. Instead of creating hard-and-fast rules for life, he writes in terms of checklists and tensions: order versus justice, City of God versus City of Man, ideal of peace versus the inevitability of armed conflict. He recognizes that the City of God, and the ability to discover and live there is difficult without the City of Man providing some kind of protection, in the form of toleration or laws. Augustine guides his readers’ decisions by respecting their ability to decide. His ideas have been a touchstone for discussions of soul and state for centuries since.

Another political writer whose fame rivals Augustine’s is Machiavelli. The Renaissance-era Florentine was not ushered into a powerful clerical position like Augustine; he was freshly released from prison and looking for a job when he wrote The Prince. And unlike Augustine, who could devote hundreds of pages to his theories of statecraft, Machiavelli had to be humble, brief, and direct. 

Machiavelli was a pragmatist who managed to dispense with some of the agonizing difficulties that Augustine experienced as he tried to reconcile God’s omnipotence with human freedom; the City of God and the City of Man. Where Augustine used reason as an attempt to make sense of the tensions (reason was arguably a competing deity alongside God for him), Machiavelli dispensed with the pretense that the ideal state could ever be obtained. In politics, there was no competition between ideals and on-the-ground realities, or even between morality and politics. The two could not be reconciled, and to try means losing a lightness of being that is indispensable to executing grand strategy. Machiavelli says, in essence, “Just accept that a certain proportion of crush-and-caress is necessary, and that ruling well involves learning to do so judiciously.” He gave up the laborious Augustinian hunt for the perfect theoretical solution.

Augustine and Machiavelli have arguably stirred up more thoughts about politics and war than any other in the Western thought. The main difference between them was that hammering out the tensions wore heavy on Augustine, whereas Machiavelli simply did not sweat it. Instead of parsing out how God’s will and man’s will interact, Machiavelli changed the formula to half human action, half fate. He took the infinitude of fate in stride and focused on the realm of human decisions, where action was actually possible.

Common sense is like oxygen: The higher up into the heights of power you climb, the less of it there is. Foxes who know many things might be better predictors of future events, but hedgehogs who know one big thing tend to climb the ranks of organizations far faster. What this means is we end up with a lot of hedgehogs in power. They have their mind on one big thing and fail to consider matters of context.

Ordinary people often manage to traverse the bridge between fox and hedgehog better than the powerful. The more powerful people become, the further they are tempted to rely on their inner hedgehog or fox. Those who tend toward the fox attempt to consolidate and retain power, sniffing out attempts to supplant them. We see this in Artabanus, Xerxes’ advisor. The hedgehogs, by contrast, often get locked into a hunger for the infinite, and historically, that has meant looking for endless glory, charging forward to expand their empires. Common sense dissipates at either extreme.

Abraham Lincoln was the greatest United States president and one of the world’s most gifted strategists. What made Lincoln remarkable was not simply his ability to have two contradictory ideas in his head and still function, but to do so as one of the most powerful men in the world at that time. He could cross the bridge between infinite ends and limited means with regularity, between hedgehog thinking and fox thinking.

Spielberg’s 2012 film Lincoln captures some of the tensions that Lincoln managed brilliantly, as he cajoled, bribed, and strong-armed in order to move the slavery-abolishing 13th Amendment through the House of Representatives. When Thaddeus Stevens, played by Tommy Lee Jones, pressed Lincoln (played by Daniel Day-Lewis) to explain how he could resort to such cunning, deceptive means to accomplish his lofty ends, this was Lincoln’s response:

[A] compass . . . [will] point you true north from where you’re standing, but it’s got no advice about the swamps and deserts and chasms that you’ll encounter along the way. If in pursuit of your destination, you plunge ahead, heedless of obstacles, and achieve nothing more than to sink in a swamp . . . , [then] what’s the use of knowing true north?

It is likely that this response is more artistic liberty than historical record, but it captures the spirit of Lincoln and the necessity of infinite ends connecting with limited means.

Lincoln was remarkably gifted in a way that many leaders across history have not been: to move shrewdly between hedgehog and fox, and keep your bearings in the process is no small feat. A review of the historical record reveals that most either become an entrenched hedgehog or fox. Whatever works, the leader tends to lean into it. As his star rises, he becomes self-conscious about the on-looking masses, and his flexibility in movement diminishes. In a strange paradox, he becomes a prisoner to his own growing influence. Xerxes became a headstrong hedgehog in his pursuit of infinites like military glory. So did Napoleon as he set his sights on Russia. He failed to traverse the bridge back to the fox side and realize that his chasing Russia was like a dog chasing a car: The dog has no idea what to do with the car even when he manages to catch it.

The bridge between infinite ends and limited means is a scary one to build. It can be disorienting, which is why people, especially the powerful, stay on one side of the chasm or the other. There is often a great deal to lose. But even for the vast majority who never ascend to the heights of power, the dynamics of grand strategy remain: Keeping two opposing ideas in mind (infinite ends and limited means) and finding ways to connect them while still functioning with clarity and levity.