The strength of a culture’s norms and punishments isn’t random. It has a secret logic that has been hiding in plain sight.
Though they were separated by miles and, in some cases, decades or centuries, the tight cultures of Sparta, the Nahua, and Singapore faced a common fate: Each had (or has) to deal with a high degree of threat, whether from Mother Nature and her constant fury of disasters, diseases, and food scarcity, or from human nature and the chaos caused by invasions and internal conflicts. And when we look at the loose cultures of New Zealand, Athens, and the Copper Inuit, we see the opposite pattern: These groups had (or have) the luxury of facing far fewer threats. They generally had the safety to explore new ideas, accept newcomers, and tolerate a wide range of behavior.
Herein lies the hidden rationale behind tight and loose cultures: Whether they dwelled in the ancient past or exist in the modern era, groups that deal with many ecological and historical threats need to do everything they can to create order in the face of chaos. Take, for example, societies like the Nahua, which are highly dependent on agriculture for their survival. When crops are bountiful, life is good. When there’s a lasting drought, life is unpredictable and harsh; people suffer and die. It stands to reason that groups that are disciplined and that punish people who don’t follow norms are better able to coordinate to cultivate crops and increase their chances of survival. By contrast, hunter-gatherers like the Inuit are highly self-reliant, with each family being responsible for foraging food; consequently, they don’t have to coordinate their efforts. Strong rules and punishments, in effect, aren’t as necessary. Beyond the Nahua and Inuit, many other groups show this same cultural logic. The Temne people of Sierra Leone, for example, rely on agricultural output for survival and thus require strict conformity to their rules, whereas the Eskimo of Baffin Island, a hunting society, allow members considerably more latitude.
Food, of course, is just one of many basic resources that human groups depend on for survival. Groups must protect themselves from many other threats besides starvation, including natural disasters, territorial threats, overpopulation, scarce natural resources, and pathogens. In fact, considering the innumerable wars that have taken place, the frequency of Mother Nature’s fury, and the number of communicable diseases that have existed, it’s a wonder that humans have been able to survive. How did they do it?
The emergence of social norms—a particularly human invention—is the key to this evolutionary puzzle. Strong norms are needed to cultivate the societal order that is necessary for surviving the most difficult circumstances. In contexts where there are fewer threats and thus less of a need for coordination, strong norms don’t materialize.
Think about a time when you were packed into a crowded elevator. How did you feel and act? You were probably monitoring your behavior, trying not to fidget too much, or suppressing a laugh at something funny you were thinking about. Maybe you were irritated by fellow passengers doing weird things, like singing with their headphones on, taking up too much room, or divulging personal details to a friend on the phone.
Some countries are a lot like that crowded elevator. People live in small spaces in close proximity to their neighbors, contending with packed streets and cheek-to-jowl buses and trains. Compare Singapore, with its astonishing population density of over twenty thousand people per square mile as of 2016, with Iceland, which has only eight people per square mile. Or imagine being in Japan, with over eight hundred people per square mile, as compared with New Zealand, where there are more sheep than people (about six sheep per person, to be precise) and about forty-five people per square mile.
Population density varies dramatically around the globe. In many countries, it’s dictated by topography or other geographical features. India is a case in point. The country has an impressively high population density of over a thousand people per square mile. The Himalayas, which comprise about 16 percent of India’s territorial area, are far too cold for humans to survive. Because flatter areas have better access to water, which is ideal for human settlement, they’ve ended up with the most inhabitants. Similarly, given that around 70 percent of Japan is covered in uninhabitable mountains, and less than 15 percent of it is suitable for agriculture, residents cope with very little space. Switzerland, one of the most mountainous areas in Europe—and home to the Alps, which cover three-fifths of the country—copes with a high population density of over five hundred people per square mile.
High population density is a basic human threat. In societies where personal space is hard to come by, there’s great potential for chaos and conflict. Even lab rats have been found to get stressed out when forced to live in close quarters: Female rats have more trouble carrying pregnancies to term, and male rats show symptoms ranging from sexual deviance to cannibalism.
Fortunately, humans, unlike rats, evolved to create strong social norms to minimize conflict and organize chaos when they’re packed in tight, so they don’t have to resort to cannibalism or other antisocial behaviors. Meanwhile, societies with low population density (such as Australia, Brazil, Venezuela, and New Zealand) can afford to be much looser. I’ve found that nations evolve this way: Areas that were populous in 1500, such as Pakistan and India, are tighter today, while Australia and Brazil, the least populous areas studied in 1500, are currently two of the loosest countries. Present-day population density, as well as predicted future population pressures, are also linked to countries’ tightness scores. In short, the more packed in you are as a country, the stronger your rules.
The effects of population density trickle down and affect seemingly arbitrary aspects of society. Let’s revisit Singapore’s ban on selling gum. It seems preposterous to most outsiders, but the country’s high population density suggests why this ban makes sense. During the 1980s, city workers struggled to keep up with cleaning chewing gum waste, which became a public crisis. The sticky wads gummed up mailboxes and elevator buttons, and even jammed apartment keyholes and the sensors on commuter train doors, causing frequent malfunctions. In a place with so many mouths per square mile, the solution was simple: Get rid of the temptation. By 1992, the sale of gum was prohibited in Singapore, and people caught selling the chewy treat faced hefty fines. The ban led to some frustration at first, but today it’s widely upheld. And if you lived among more than twenty thousand people per square mile, chances are that you’d support it, too.
When you look at a map of the world, there are some striking differences between nations that have and have not experienced chronic threats of invasion. In his book The Revenge of Geography, Robert Kaplan reminds us that the United States—with its safe separation from other continents by two large oceans—has felt few threats from outsiders throughout its history. The same is also true of New Zealand and Australia. Of course, these nations have had their share of traumatic conflict, but, overall, they haven’t faced chronic threats from external forces trying to bust down their doors.
But other modern nations have had conflict on their soil for centuries. Take Germany. The Thirty Years’ War in the early seventeenth century killed off 20 percent of Germany’s (then Prussian) population; the Franco-Prussian War left tens of thousands of German soldiers dead; and the Soviet occupation of East Germany resulted in almost eleven million Germans displaced by 1950, more than six hundred thousand killed, and over two million who remain unaccounted for.
Conflict has been particularly prevalent in Asia. China has experienced massive conflict throughout its history, with an exceedingly long list of battles beginning in 206 BC during the Han Dynasty, extending into the Yuan and Ming Dynasties, and later into the Qing Dynasty (1644–1912). Thereafter, during the Second Sino-Japanese War (1937–1945), China suffered millions of deaths, widespread starvation, and devastation to its infrastructure. Today, China’s location makes territorial threat a constant source of anxiety. It borders fourteen countries, and has had disputes with each of them.
Korea also has been repeatedly clobbered by its neighbors. The famous Korean proverb “When whales fight, the shrimp’s back is broken” describes South Korea’s predicament of being collateral damage over the course of many centuries while its neighboring countries have fought one another. Korea was invaded by Japan in the late 1500s and the Manchus in the early 1600s, and was the fighting ground for the beginning of the First Sino-Japanese War in the 1890s. In more recent history, Korea suffered under Japanese rule from 1910 to 1945, and later, more than a million South Korean civilians and military personnel died in the Korean War, which lasted from 1950 to 1953.
Countries in the Middle East have repeatedly faced invasions and colonization from foreign powers. Since the decline of its pharaohs many centuries ago, Egypt has endured the wrath of the Turks, Persians, Romans, Arabs, Greeks, French, and English. Both Pakistan and India have histories rife with conflicts on their own soil. India has had significant violent conflicts with Pakistan and China regarding contested territories, and Pakistan has had numerous border disputes with Afghanistan.
How could inhabitants of these countries best survive such hostile conditions? Nations with a history of external conflict, I speculated, would by necessity evolve to be tighter.
When nations face the possibility of invasion, they must strengthen internal order to ensure a united, coordinated front against the enemy. Tight social norms are essential to this defense. Presumably, in the past, groups that didn’t have strong norms or punish norm violators would be at risk of buckling under these chronic high-pressure situations. “The exigencies of war with outsiders are what make peace inside, lest internal discord should weaken the we-group for war,” remarked the American social scientist William Graham Sumner in 1906. Darwin himself also speculated that war with outsiders would create evolutionary pressures for cooperation and unity.
I set out to see if, indeed, there was a connection between a country’s level of tightness and its history of territorial threat. Using the International Crisis Behavior database, I found data on territorial conflicts between nations between 1918 and 2001. My hypothesis was very specific: I speculated that the threat of conflict on a nation’s own territory—not the overall amount of conflict the nation is involved with abroad—would, over the last century, correlate with strength of social norms.
Even when taking into account nations’ wealth, I found that nations with a higher number of territorial threats over the last hundred years indeed were tighter than those with fewer territorial threats. India, China, and Pakistan had high levels of territorial threat and were some of the tightest among the nations surveyed. Meanwhile, New Zealand and the United States were low in territorial threat and high in looseness. Notably, even though the United States scores high on involvement in international conflicts abroad, this tendency to be the “world’s policeman” does not correlate at all with tightness.
Groups don’t only have to deal with human threats of internal and external conflict. They also have to face natural threats: droughts, floods, landslides, tsunamis, typhoons, cyclones, volcanic eruptions, and earthquakes. China, for example, has lost nearly 450,000 lives in the past fifty years to natural disasters (twenty-five times more than the United States), in part due to the typhoons that torment its long coastline. India loses about $10 billion each year due to disasters, including droughts, landslides, flash floods, and cyclones. Indonesia’s seventeen thousand islands are located between the world’s two most seismically active areas, the Pacific Ring of Fire and the Alpide Belt, making them vulnerable to some of the world’s worst natural disasters, including earthquakes.
Japan has also been one of Mother Nature’s favorite targets. Throughout its history, Japan has experienced an onslaught of natural disasters. A combination of cold weather and volcanic activity led to the Kangi Famine from 1229 to 1232. During the Edo Period (1603–1868), more than 150 famines hit Japan, leaving at least hundreds of thousands dead. In the modern era, Japan has suffered from several devastating earthquakes, including the 2011 magnitude-nine Tohoku earthquake and tsunami, which killed thousands of people and cost Japan over $200 billion. Millions of survivors were forced to cope without water, heat, or food for days.
Nations like Japan need stronger norms to provide the order and coordination required to recover from chronic natural disasters. Without strong norms, people would be tempted to go rogue in such dire circumstances—looking out only for themselves or their immediate family, for example, by engaging in looting—causing total chaos. But with strong norms and punishments for deviance, such nations are in a much better position to cope and survive.
As a case in point, after the 1995 Kobe earthquake, over one million people stepped up to help those in need. After the 2011 Tohoku earthquake, volunteer administrators were so overwhelmed by offers of aid from ordinary citizens that they had to turn some away. Even the Japanese mafia—the yakuza—helped with relief efforts, sending in supply trucks and offering refuge to stranded victims. This impressive solidarity in response to natural disasters isn’t unique to Japan. Other countries, including Malaysia—another tight nation prone to floods, tsunamis, landslides, forest fires, and cyclones—have had to come together as a well-coordinated nation in the face of disasters. Strong norms and punishments help in this quest.
By contrast, cultures that don’t face chronic disasters don’t necessarily need to have such a well-coordinated cultural machine, and thus can afford to be loose. Data I’ve analyzed support this hypothesis: Vulnerability to natural disasters, as measured by the Environmental Sustainability Index, correlates strongly with tightness, even accounting for national wealth. Japan, South Korea, and Pakistan—some of the most disaster-plagued nations—are also among the tightest. By contrast, nations like Ukraine, Hungary, and Greece, which have remained relatively unscathed by natural disasters, have looser norms.
Frequent disasters have other devastating consequences. They often deplete natural resources, including arable land and drinking water supplies. Our data suggest that cultures that lack such resources are tighter than cultures that have them in abundance. The reason is simple: When cultures have few natural resources, managing them in a controlled, coordinated way is a matter of survival.
Here again, Singapore, a tight culture, is a case in point. “We faced tremendous odds with an improbable chance of survival. Singapore was not a natural country, but man-made,” writes Lee Kuan Yew, the founding father of modern Singapore, in his autobiography. Commenting on the lack of natural resources, Lee further noted that forging a “tightly knit” society was crucial: “We had one simple guiding principle for our survival, that Singapore had to be more rugged, better organized, and more efficient than others in the region.”
Lee was not a cross-cultural psychologist, but he had the right intuition. With data from the United Nations and other sources on arable land, food production, food supply, protein and fat supply, food deprivation, air quality, and water quality, we can see whether tight cultures have a lack of natural resources. The results show that countries cursed with fewer natural resources—from farmland to food supply to water—are much tighter than those blessed with abundance. Of the nations I surveyed, Pakistan, India, and China, all tight, had the fewest natural resources within their territories, with high levels of food deprivation and low access to safe water. Similarly, Norway, Hong Kong, and Singapore had the smallest amounts of farmland, while Hungary, loose in our data, had abundant farmland. Israel is barely bigger than New Jersey, but it ranks as the lowest for food deprivation. Societies reasonably react to a lack of natural resources by tightening social norms, which provides more order where there could be chaos.
Anyone who has seen the movie Contagion immediately cringes at the thought of little microbes spreading to decimate large populations, and with good reason: The plot wasn’t just dreamed up by Hollywood screenwriters. Infectious diseases have menaced humans for as long as we’ve been on the planet. For thousands of years, large percentages of populations were regularly wiped out by diseases. The plague known as the “Black Death” killed at least seventy-five million people during the fourteenth century. Typhus claimed over ten million lives in the 1600s. Yellow fever killed tens of thousands during Napoleon’s reign. A smallpox outbreak led hundreds of thousands of people to perish at the end of the eighteenth century, and the Spanish flu caused as many as fifty million deaths in the early twentieth century. Indeed, throughout history, pathogens that were brought by groups to new territories often wiped out entire populations who lacked immunity to them, as discussed in Jared Diamond’s critically acclaimed book Guns, Germs, and Steel.
Today, advances in modern medicine have dramatically reduced the risk of death from pathogens, but societies still aren’t invincible to viral diseases. An estimated thirty-five million people have been killed by AIDS, and more than thirty million people globally have died from tuberculosis-related illnesses since it was declared a global emergency by the World Health Organization in 1993. And to this day, millions of people contract malaria. With more than 200 million cases in 2016 alone, malaria remains a menace worldwide.
From an evolutionary perspective, humans needed to find ways to survive these threats. Our bodies did so by perfecting sophisticated physiological immune responses. In modern societies, we have likewise developed cutting-edge technologies to try to contain pathogens, including antibiotics, water treatments, infectious disease modeling, genomics, and electronic surveillance systems. Even food customs have also evolved in countries where infectious diseases have been rampant, such as dousing food with spices that can act as powerful antibiotics that kill off nasty bacteria.
Strong social norms turn out to be another shield for stopping germs. For example, when people feel more vulnerable to diseases, they tend to have a higher sense of cultural superiority and have more negative views toward other ethnic groups, presumably to avoid the transmission of diseases. And research shows that in times of high levels of disease threat and infant mortality, parents teach their children to be compliant and obedient. By restricting the range of permissible behavior, strong social norms help thwart the spread of disease and help people mount a coordinated response if and when outbreaks strike. By contrast, loose norms, which allow for permissiveness and exploration, can promote risky behaviors that expose people to deadly pathogens and thwart an effective response.
Singapore’s response to the 2003 SARS outbreak is a case in point. Soon after SARS hit, the Singaporean government quickly implemented strict rules and restrictions on people’s movement and somewhat intrusive early-detection measures, such as monitoring people’s temperature at schools, work, and households (thermometers were distributed to over a million people). Webcams were even installed in the homes of quarantined citizens, who were phoned at random points during the day and required to present themselves in front of the camera to ensure they didn’t leave home. Similarly, following the 2009 influenza outbreak in Japan, officials quickly set up medical counseling and outpatient centers to detect and prevent the spread of the virus. They also enacted temporary school closures, border screening at airports, and influenza surveillance systems throughout cities.
While this level of monitoring and restrictions may seem excessive to outsiders, they help countries with a history of pathogen outbreaks to avoid contamination. Across 230 geopolitical regions dating back to the 1940s, I’ve found that tighter countries, including Pakistan, India, Turkey, and Malaysia, have indeed been more burdened by infectious diseases, from malaria to typhus to tuberculosis, than loose countries such as Australia, Greece, Hungary, and Poland.
In all, the data show that many ecological and human threats—from conflict to Mother Nature’s fury—are related to tightness-looseness. Indeed, the link between threat and tightness isn’t just found in modern nations—we’ve found it in our studies of traditional societies as well. Of course, physical threats are not the only ones that might drive tightness. In other cases, the “threat” that impels social order may be spiritual in nature. Nearly all religious traditions include extensive and detailed prohibitions to keep believers from engaging in behaviors that might threaten their purity and even afterlife. Religion tends to breed tightness, both today and in ancient history, according to our data. Beyond the codification of right and wrong, the belief in the Almighty inculcates the same tight accountability that security cameras bring to public spaces.
Societies evolve to be tighter when they face chronic threats over the course of many years, but I’ve shown they also tighten up when they face a sudden collective threat—even if it’s short-lived. In 2013, right after the Boston Marathon bombing, which left three dead and more than a hundred wounded, Bostonians showed incredible unity, with many residents rushing to the site of the attack to help those lost or injured. Some marathon participants kept running past the finish line to the closest hospital to donate blood. After this tragedy, the phrase “Boston Strong” took hold as a symbol of the city’s cohesion, strength, and pride.
I set up a field study in Boston to test whether the city’s cultural norms had tightened in response to the event. People who reported being the most affected by the bombings were indeed more likely to report that the United States needed to have stronger social norms. They also reported that the American way of life needs to be protected against foreign influence, there should be more restrictions over people entering the country, and the United States is superior to other countries. These are all attitudes we see in nations that face chronic invasions.
Even the fear of a threat induced in the lab is sufficient for people to tighten up. In one study, I randomly assigned people to read one of two versions of a fictitious news article. Some read that their university was implementing a new terror alert system due to its proximity to the nation’s capital, which could be attacked. Others in the study read that a foreign university was implementing a new terror alert system but that their university had rejected this proposal, given strong evidence against the school’s becoming a target of terror. Compared with the students who read that their campus was safe, those who read that a terrorist attack was possible became significantly more biased against people who were seen as “deviant” and more likely to rate their culture as superior to others.
The fear of threat can even cause people’s brains to sync up to help them coordinate. In a study we conducted in China, my research team and I designed three fictitious articles, which our participants thought were real. Some of our Chinese participants read an article about how Japan posed a severe threat to China in the coming decade, while others read an article about a conflict between two other countries (Ethiopia and Eritrea) or an article about China, but without any mention of external threat. Then, participants in each group were given a task that required them to coordinate quickly—namely, they had to count out loud at the exact same pace together, over many trials. During this task, we used a state-of-the-art neuroscience technique called “hyperscanning” to simultaneously record the brain waves of the interacting partners. When we analyzed our data, we found that Chinese who’d read about a threat from Japan showed higher neural synchrony—specifically in their gamma waves, which signify fear—and this helped them coordinate faster on the task. People’s neurons, it seems, begin to march in sync under external threat.
Even people who are made to feel like there’s high population density in their immediate environment—like in Singapore—become tighter, at least temporarily. In another experiment, students at the University of Maryland were given one of two versions of a fictitious article purported to be from the school newspaper. Both articles gave a detailed ranking of population density of ten different U.S. universities from the most to the least dense, but with one small twist. In one condition, students read that UMD had the highest population density of all campuses listed, with a whopping 1,500 people per square mile. In another condition, they read that UMD had one of the lowest population densities—a mere 440 people per square mile. Next, we asked the students to evaluate a variety of norm violations on campus, such as littering in public places, fighting at a sports game, talking loudly at the library, or driving under the influence of alcohol. Across the board, those who thought they were going to school on a crowded campus had more negative reactions to people breaking norms. Just by suggesting their environment had very high density, we induced these Americans to become tighter like Singaporeans, at least temporarily.
In 2011, I took this “threat priming” paradigm into the field. When the previously mentioned pathogen-scare movie Contagion hit the movie theaters, I planted research assistants outside movie theaters all around Washington, D.C., to study people’s reactions. Contagion wasn’t just a big box-office hit; it was commended by scientists for its realism. It actually made viewers feel that they were part of a pandemic. I decided to take advantage of this feeling by surveying people who’d either just seen the film, or were about to see it. Sure enough, people who’d just seen the film and virtually experienced a pandemic showed more hostility toward social deviants than people who hadn’t yet entered the theater.
These studies show that activating a threat can temporarily tighten the mind, in much the same manner that chronic threats cause tight cultures. It’s only when a threat subsides that our need for strong norms subsides. Indeed, our computer simulations of how groups respond to threat show exactly this: A temporary increase in threat can cause a dramatic rise in tightness, but groups will revert to looseness unless the threat recurs.
Importantly, this research highlights that tightness-looseness is dynamic—it can change over time. As threats crop up, groups tighten. As threats subside, groups loosen. Threats don’t even need to be real. As long as people perceive a threat, the perception can be as powerful as objective reality. In fact, long before Donald Trump, Marine Le Pen, or Viktor Orbán, politicians have been hyping up threats to tighten groups for centuries.
Threat might be one of the biggest drivers of cultural tightness. But other factors can pull cultures in the opposite direction.
As a general rule, diversity exposes people to multiple perspectives and ultimately makes us more tolerant of a wider range of behaviors. Take Israel, for example. Crammed into just over eight thousand square miles are nearly 8.6 million people—that’s about a thousand people per square mile. When Israel was founded, its settlers faced rampant malaria, typhus, and cholera. The country has fought numerous wars, mostly due to territorial issues and the long-held animosity between Arabs and Israelis, which continues to this day. Yet Israel is relatively loose, with its high levels of informality and chronic attempts to circumvent rules. Why?
There are multiple possibilities, but one stands out as especially compelling: Israel is highly diverse. Seventy-five percent of the nation is Jewish, 20 percent is Arab, and the remaining 5 percent are a mix of non-Arab Christian and Baha’i, among other groups. The country has high levels of ethnic diversity, with significant percentages of the citizenry hailing from Eastern Europe, Africa, and the Middle East. With so many different groups with different coexisting norms, it is hard to agree on any one standard for behavior. This general principle also applies to the traditional societies we encountered in Chapter 2. Ancient Athens, a bastion of looseness, also had encounters with many foreign countries thanks to its extensive trading.
Does diversity correlate with a country’s looseness? Our data suggest that it does, at least up to a point. Nations that are heterogeneous on multiple markers, such as ethnicity and language, are much looser than those that are homogeneous, we’ve found, but an important caveat is in order. When diversity gets to be extreme, as it is in Pakistan, which has at least six major ethnic groups and over twenty spoken languages, and India, with its twenty-two official languages and hundreds of dialects, diversity can cause conflict, which, as we know, requires strict norms to manage. When diversity gets to be very high, tightness begins to increase markedly.
Another possible explanation for Israel’s relative looseness is its fierce tradition of debate. As the joke goes, a Jew was asked by a non-Jew why Jews always answer a question with another question. “Why not?” he replied. Debate and dissent, which mandate the exploration of multiple perspectives, promote looseness and the rejection of dogma. (To quote another popular adage: Ask two Jews, get three opinions.) In addition, Israel is a young, exploratory “start-up nation” made up of settlers who had the chutzpah to dive into something new, risky, and unknown.
Like Israel, the Netherlands also evolved to be quite loose, in part due to its history of high levels of mobility and exposure to multiculturalism. Its coastal location has promoted extensive travel among its citizens and a high dependency on international trade, giving the Dutch centuries of rich experiences with other cultures. The Dutch traded with France, Portugal, and countries around the Baltic Sea and the Mediterranean. Trade with Spain likewise flourished, and the Dutch controlled much of the trade with the English colonies in North America. With its tremendous mobility around the world and exposure to many different cultures, the Netherlands evolved to be tolerant. When the sale of books was restricted throughout Europe during the seventeenth century, booksellers flocked to the Netherlands, where censorship laws were far less strict. It’s also perhaps no surprise that the world’s first multinational corporation, the Dutch East India Company (VOC), which commercially linked the East and West through the seventeenth and eighteenth centuries, was also founded in the Netherlands.
Thanks in large part to its location and trading activity, the Netherlands has become home to an eclectic mix of ethnic, racial, and religious groups, which may have contributed to its looseness. For centuries, the Netherlands welcomed refugees from all over Europe, including French Protestants, Portuguese and German Jews, and English separatists, among many others. Today, over 20 percent of the population comes from abroad, including from other European countries, Indonesia, Turkey, Suriname, Morocco, and the Caribbean. The Netherlands is a veritable melting pot.
Tightness and looseness can evolve in different ways, but the outcome isn’t random. Ecological and historical threats—real or perceived—push groups to be tighter, while diversity, mobility, and multicultural contact with outsiders foster looseness. Of course, these relationships aren’t deterministic—they’re only statistically probabilistic—and they needn’t be the only factors that affect norm strength. But they help detect important patterns that have long remained hidden.