In the tense hours of September 26, 1983, a chilling alarm echoed through the Soviet Union’s early-warning system: intercontinental ballistic missiles were allegedly launched from the United States. Duty officer Stanislav Petrov, a man who likely hadn’t formally studied Bayes’ theorem, was faced with an unimaginable decision. His orders dictated reporting the warning, a move that could have triggered a nuclear counterattack. Yet, Petrov instinctively employed Bayesian reasoning. He didn’t react solely to the alarming new information. Instead, he considered the broader context: the low probability of a nuclear attack on any given night, perhaps similar to the chance of equipment malfunction. Adding to his skepticism, the alert itself seemed unusual – only five missiles detected? Surely a full-scale first strike would involve far more. Based on this reasoning, Petrov chose not to report the alert, potentially averting global catastrophe.
This real-world scenario perfectly illustrates Why Is Bayesian reasoning such a powerful tool. It’s not just a statistical method; it’s a framework for interpreting new information wisely. Bayesian reasoning offers a set of “best practices” for navigating the complexities of information and decision-making. It starts with understanding the big picture, establishing a solid foundation of your existing knowledge. Then, it emphasizes a cautious approach to new information, urging you to avoid impulsive conclusions. Crucially, it teaches you to discern when new data truly alters your fundamental assumptions and when it’s merely noise. It’s about recognizing the overwhelming impact of sensational news and placing it within a realistic, broader context.
Think of it like mise en place in cooking. You keep your pre-existing knowledge separate from the fresh, incoming data. Remember, raw information, like raw ingredients, can change significantly when processed. But the true strength of the Bayesian approach isn’t just procedural; it’s transformative. It encourages us to replace rigid “facts” in our minds with probabilities. While some might be absolutely convinced of extreme positions – “GMOs are inherently bad,” or “Person X is completely trustworthy” – a Bayesian thinker assigns probabilities to these claims. They don’t build an inflexible worldview. Instead, by continuously updating these probabilities based on new evidence, they gradually approach a more accurate and useful understanding of reality. The process of learning and refining our understanding is never truly complete.
Why is considering different perspectives crucial for rational thinking? This cartoon highlights the importance of questioning initial assumptions and being open to diverse viewpoints to avoid narrow or biased thinking.
When applied to specific questions – “Why is Tesla a good investment?” or “Why is the Delta variant so concerning?” – the techniques promoted by rationality experts become incredibly insightful. The rationality movement, however, extends beyond individual problem-solving; it has evolved into a social movement, a “rationality community.” These “rationalists” share a common language. A high compliment within this community is to say you’ve caused someone to “revise their priors,” meaning you’ve changed their deeply held prior assumptions. Imagine a mental map where possibilities are mountains – revising priors means those mountains shift in probabilistic height. They might also discuss holding a view “on the margin,” indicating that an idea is considered as a slight adjustment to pre-existing beliefs when new information arises. (Economists use “marginal utility” similarly – the joy of the first bite of food is higher than the tenth). “Updating” opinions is another common phrase, borrowed from “Bayesian updating,” which rationalists use to normalize admitting mistakes as a positive step towards better understanding. This language creates a sense of deliberate, constructive thinking, like building a robust structure. Economist Tyler Cowen, reflecting on the Jeffrey Epstein case, wrote in 2019: “Every so often a story comes along that causes me to update my priors. I am now, at the margin, more inclined to the view that what keeps many people on good behavior is simply inertia.”
In Silicon Valley, “Update Your Priors” T-shirts are common, but adopting the language of rationality doesn’t automatically make you a rational thinker. Someone can superficially discuss base rates or claim to be revising priors while holding onto firmly entrenched opinions. Google provides the illusion of instant expertise, allowing someone to seem like they’ve mastered a complex field in days. However, this doesn’t equate to genuine understanding. Knowing who the respected researchers are, or the informal discussions within a field, requires deeper engagement. There’s a significant difference between reading about surgery and being a surgeon; a surgeon’s informed priors are what truly matter. In a conversation with Ezra Klein, Cowen, a voracious reader and creator of the blog Marginal Revolution, pointed out that the rationality movement often embodies a “culturally specific way of viewing the world”—primarily, the culture of online debate and argumentation. Cowen argues that true understanding requires firsthand experience, not just reading. His own priors are shaped by visiting nearly a hundred countries, including experiences like being caught in a drug gang shootout in Brazil.
It’s clear we desire rationality in our leaders. Yet, the perception that rationalists are detached from real-world experience can be unsettling when considering rational leaders in positions of power. Would they become lost in data matrices, more focused on their mental map of reality than the people within it? A satirical sketch by Mitchell and Webb illustrates this concern: a government minister, tasked with ending a recession, asks his analysts if “killing all the poor” has been considered. “I’m not saying do it—I’m just saying run it through the computer and see if it would work,” he clarifies. (When told it wouldn’t, he proposes “blue-skying” an even more absurd idea: “Raise V.A.T. and kill all the poor.”) This caricature reflects a common skepticism towards rationality as a dominant value system. During the Affordable Care Act debates, fears arose among conservatives about “death panels”—committees of rational experts who might suggest cost-cutting measures like denying care to the elderly. This fear, while exaggerated, touched on a real societal discomfort: the fact that a significant portion of healthcare spending occurs in the final years of life. Rational thinkers often have to address uncomfortable truths, and sometimes, in doing so, they can appear insensitive.
However, in our personal lives, the dynamics of rationality are different. Friends lack direct power over us; they can only guide and influence. In Pride and Prejudice, Elizabeth Bennet is intelligent and thoughtful, but her friend Charlotte Lucas embodies rationality. Charlotte uses Bayesian reasoning intuitively. When Mr. Darcy appears arrogant at a party, Charlotte advises Lizzy to consider the bigger picture: Darcy is “so very fine a young man, with family, fortune, everything in his favour.” Therefore, the prior expectation should be that wealthy, attractive individuals might act proud at social events. Such behavior isn’t inherently revealing of his true character. When Charlotte marries Mr. Collins, a clergyman with a stable income but an irritating personality, Lizzy is shocked. But Charlotte explains that marital success depends on numerous factors, including financial security, and believes her chances of happiness are “as fair as most people can boast.” (Modern statistics support her: while divorce rates are high, they are lower among higher-income groups.) Charlotte’s example prompts Lizzy to re-evaluate Mr. Darcy, discovering his flaws are predictable, but his virtues are exceptional. Rom-coms often depict passionate friends urging characters to “follow their hearts,” but Jane Austen understood the value of rational friends.
Indeed, as Charlotte demonstrates, a kind rationalist can be remarkably courteous, suggesting deeper virtues. Julia Galef describes an interaction on the now-defunct website ChangeAView. A male blogger, accused of sexism, initially defended himself. Then, in a post titled “Why It’s Plausible I’m Wrong,” he meticulously summarized the arguments against him. Ultimately, he admitted his error, apologizing to those he offended and those who had supported his now-acknowledged mistake. Impressed by his sincere open-mindedness, Galef sent him a private message. They eventually got engaged.
This illustrates why is the rationality community a potential setting for a modern Austen novel. But how much credit should rationality receive for Galef and her husband’s connection? It played a part, but rationality isn’t the sole explanation for the qualities she admired. The author initially admired a friend, Greg, for his rationality, but has since revised this view. It’s not rationality itself that makes Greg curious, truthful, honest, careful, perceptive, and fair, but rather the other way around. These underlying character traits enable genuine rationality.
In books like Rationality and The Scout Mindset, irrationality is often portrayed as a behavioral flaw that can be corrected through education. This is true in some instances, but not universally. The author recalls his mother, a perceptive and intelligent woman, but not particularly rational. When a cardinal bird repeatedly flew into their living room window, she became convinced it was an omen, waiting anxiously for its return. Minor events – a torn dollar bill, a flat tire – could darken her mood for days. As a voter, parent, employee, and friend, she was driven by emotion. She had a turbulent, poetic, and complex personality. A book on rationality likely wouldn’t have helped her significantly. Such books are often best suited for those already inclined towards rational thinking.
In contrast, the author’s father is a doctor and scientist, naturally rational. He told his son Santa Claus wasn’t real early on and engaged in discussions about physics, computers, and Star Trek, identifying as Spocks rather than Kirks. Years after their divorce, when the author’s mother needed to be moved from a hospital to rehab, and the author felt overwhelmed and confused about how to proceed, his father patiently, methodically, and thoughtfully guided him through the options. He analyzed each potential path, separating certainties from possibilities, managing the complexities, and communicating everything calmly. This was entirely consistent with his character.
Having spent years striving for rationality himself, the author reflects on why is he still felt paralyzed when navigating his mother’s care. Greg explains that in his business, rational thought alone isn’t enough. Someone accustomed to leisurely contemplation might struggle to reason under pressure. Someone skilled at rational conclusions might hesitate when needing to commit. Greg’s hedge-fund colleagues value someone “commercial”—not just rational, but also timely and decisive. An effective rationalist must act decisively in the face of uncertainty, like shorting a market or choosing a rehab center, even within a world of Bayesian probabilities. The author rationally understands the low risk of coronavirus to his young son, yet still hesitated enrolling him in daycare, a place for crucial social development. Knowing the right course of action doesn’t always translate to easy execution.
Acting on conclusions is one challenge. But a rationalist must also be “metarational”—willing to defer to others with superior knowledge or expertise. This too is harder than it seems. We intellectually grasp the need for specialization in a complex society. We acknowledge the limitations of our own knowledge. Yet, like Gurri’s populists, rationalists can engage in contrarianism, believing only their own opinions are valid. Deferring to others, like acting decisively, involves the entire personality. The author could be metarational with his father because he trusted not just his intellect, but also his good intentions and care. He knew his father, unlike the minister in the Mitchell and Webb sketch, would genuinely care and think deeply about the problem. Care is essential, but insufficient alone. Between them, they possessed the necessary elements: mutual trust, shared concern, and a commitment to reason and action.
The realities of rationality are humbling. To know, to want, and to use knowledge to achieve desires—it sounds simple. But it outlines a series of escalating challenges. In seeking facts, we work with probabilities. Unable to know everything ourselves, we rely on those who care enough to learn. We must act amidst uncertainty and act promptly—sometimes alone, often together. For all this to happen, rationality is necessary, but not sufficient. Thinking straight is only the beginning of the work.
