We are all familiar with the pop psychology mainstay of left-brained and right-brained thinking. The conventional breakdown posed the left side as rational and the right side as emotional. Psychiatrist and former Oxford literary scholar Iain McGilchrist argues that pop psychologists and even many neuroscientists have failed to pull back the veil and help us see the hemispheric brain for what it is and how it helps us come to know. After 20 years of brain research and combing through thousands of relevant research articles, McGilchrist shows us what the relationship is between the right hemisphere (the “master”) and the left hemisphere (the “emissary”). He also shows us what it reveals about who we are, and how the hemispheric relationship has shaped the course of Western history.

For decades, pop psychology has heralded the differences between the left brain and the right as a key to understanding people and their mental processes. Popular conceptions run along these lines: Left brain uses logic, right brain uses feelings; left brain is detail-oriented, right brain sees the big picture; left brain majors in language and words whereas right brain operates in terms of images and symbols; the left brain is reality based whereas the right brain is fantasy based; the left brain develops strategies while the right brain offers up possibilities; the left brain is risk-averse, whereas the right brain is risk-taking. The problem with this breakdown is that it is wrong—completely wrong. In some cases the functions described are just the opposite of what is commonly supposed.

Many neuroscientists had given up on laterality studies (looking at the hemispheres of the brain) after numerous assumptions about the left and right hemisphere functions were more or less disproven—though not before getting hijacked by pop psychologists misinforming the public. Numerous disheartened neuroscientists concluded that both hemispheres are involved in these functions and that there are no meaningful distinctions between them. In their attempt to debunk the left brain-right brain myth, however, they propagated another.

It is true that both hemispheres are involved in numerous cognitive processes, but it would be a colossal mistake to argue there are no differences between the hemispheres. The hemispheric differences are immense, have civilization-shaping ramifications, and reveal to us fundamental aspects of the human condition—some of which, as we will see, get short shrift in Western culture.

During gestation, the hemispheric division emerges fairly quickly (for humans, within the first five weeks). And unlike the skull, which begins as supple interlocked plates that fuse and harden over time, the brain within it undergoes a partial fission rather than a fusion.

The brain’s hemispheres are connected through a network of hundreds of millions of nerve fibers called the corpus callosum. Well into the 20th century, scientists assumed the corpus callosum maintained structural integrity, but more recent research has established that it’s more a bridge than a scaffold, forming interhemispheric lines of communication. In the mid-1900s, surgeons would sever this connective bundle to stop epileptic seizures—with remarkably few side effects.

Interestingly, most of the interconnected wiring is inhibitory rather than excitatory. In other words, the neural communiqués prevent one hemisphere from interfering with the other more often than they involve both hemispheres. Some scientists see this as the corpus callosum’s chief function, and many brain scans do reveal excitatory responses in one hemisphere quickly followed by lengthy inhibitory responses in the other hemisphere.

You might be tempted to predict that interhemispheric connection grows with brain size, but it’s just the opposite: The connection between the hemispheres has declined over the course of our history. We are big on brains, but short on connection between the hemispheres. The modern human brain is bigger than ever, less connected than ever, and, what is more, it has also become more asymmetrical than ever (the left hemisphere of the frontal lobe being noticeably larger than the right).

People have wondered and speculated about this asymmetry for some time. Over the course of the early and mid 1900s, scientists began to discover more and more irregularities. They noticed, for example, that the posterior portion of the left frontal lobe tends to protrude further, and that the brain is wider front-right as well as back-left. The back-left protrusion is wide enough even to tuck under the right hemisphere slightly. The overall effect is a brain that looks like someone grabbed it and gave it a sharp clockwise twist. The effect is slight but shows up in almost all human brains, earning it the moniker “Yakovlevian torque.” The brain’s asymmetry is also linked to diminishing connection between the hemispheres.

Thus, evolution has moved human brain development in an unexpected direction, one in which the hemispheres are increasingly disconnected. The corpus callosum connection has never been so tenuous, and has led many neuroscientists to conclude that the hemispheres are virtually autonomous systems. The accentuated duality improves our control and ability to manipulate our surroundings. That is a tantalizing possibility that has allowed for civilization to emerge, but as we will see, it can land us in trouble when the left hemisphere stops communicating with the right.

If the pop psychological conceptions of rational left brain-emotional right brain are bogus, but the hemispheric differences do still matter, what exactly are the distinguishing hemispheric features worthy of attention? We could, like most neuroscientists, focus our attention on the brain’s structure and function, on the brain’s whatness. It brings us into a world of objects and mechanisms (a very left brain preoccupation, as it turns out). But another way to view the differences is the quality or texture of how the hemispheres attend to the world, which is a right brain process. Ultimately, “how each hemisphere does is more important than what it does.”

The right hemisphere is the “master” of the pair, and the left hemisphere is his “emissary,” so when we ask the what questions, we are playing by the emissary’s rules, rather than the master’s. The how question shows us a new way of exploring the brain and attending to life.

So how do the hemispheres attend to the world?

The right hemisphere offers us breadth and flexibility, whereas the left brain focuses and grasps. We first are present to the world we experience (a right hemisphere process), but then the left hemisphere processes what we are experiencing and “re-presents” parts of that experience in a way that helps us “use” what is around us in order to make life more manageable and livable.

The right hemisphere is what allows us to be present to new experiences—the whole of it, whereas the left hemisphere hones in on particulars. Once a skill, whether learning a sport or an instrument, becomes familiar, the left brain renders those experiences as “known.”

Relatedly, the right hemisphere sees possibility and what is “out there” in the world, whereas the left hemisphere prizes predictability. The right hemisphere, being the more flexible, can shift to a new paradigm, but the left hemisphere resists the disruptions to the categories it has. It sticks to what it thinks it knows. New experiences, new skills, new information all change the right, but not the left. The right predicts better in the face of uncertainty, whereas the left sticks to what it knows, even when familiar solutions won’t help. Victims of right frontal lobe damage tend toward pathological intransigence, digging in their heels on an issue. They go with their immediate response, with what has worked in the past, even if a new problem requires a different tack. They will deny, sometimes angrily, any discrepancy between their grid and the evidence presented.

The right brain attention is broader, whereas the left brain is more tunneled. If the right brain offers a lantern glow, the left gives us a flashlight. We see the difference when something is “on the tip of your tongue.” The harder you try to dredge up the information, the slimmer your chances of retrieving it, because the left brain narrows the field of exploration. Usually, giving it a rest gives you the best chance of retrieval, and the memory virtually sneaks up on you at the moment you least expect. This narrowing capacity of the left hemisphere also explains why a left hemisphere stroke often results in augmented creativity.

Conversely, right hemisphere damage (which renders patients more reliant on the left hemisphere) results in an inability to expand the scope of attention. The quality of attention becomes tighter, more unbending.

The right hemisphere looks at the whole and considers context, whereas the left hemisphere looks at the parts and creates abstractions that can be used regardless of context. The right hemisphere sees individuals, whereas the left sees categories. A natural consequence is that the right hemisphere is more relationally oriented, whereas the goal of control motivates the left hemisphere. The right experiences life as living, connected, and relational, whereas the left hemisphere is anxious to create predictable mechanics.

The right hemisphere keeps us open to different ways of doing things, to adapting our way of seeing things and pivoting to new ways of viewing the world. The left brain struggles mightily, almost pathologically, against these disruptions of predictable patterns.

It’s not so much that the two hemispheres “think about” the world differently, as much as they represent two different modes of “being in” the world. More than interesting bits of trivia, the differences between the hemispheres are extremely consequential for how we live in the world as individuals and as members of a particular culture and civilization. Without realizing it, Western civilization has become overly reliant on and unwittingly trapped in left hemisphere operations that no longer communicate with the right (master) hemisphere.

In the 1800s, physicians accurately attributed speech to the brain’s left hemisphere. Where they went wrong was their presumption that the left hemisphere was the master because it did all the talking. 

The right hemisphere was long called the minor half, but a preponderance of evidence reveals just the opposite. The right hemisphere is not just co-equal with the left hemisphere, but is the left hemisphere’s master. Both left and right together enable us to know: The right takes in the whole experience, which is broken down into parts, analyzed, and abstracted into a system of belief that the left hemisphere “knows.” It creates general categories and rules that render experience more manageable. But ultimately, the left is the emissary, presenting its knowledge for the right to endorse. The right hemisphere signs off and integrates the knowledge into a holistic picture of things.

One key that clues us in to the right hemisphere’s position as master is that it engages with new experiences. Without the right hemisphere being present to those experiences, there would be no knowledge of anything in the first place. The right hemisphere provides form, without which the left hemisphere could provide no structure. The right hemisphere has to present before the left hemisphere can re-present. Even prior to the left hemisphere’s use of referential language to describe experiences (left hemisphere’s most influential instrument), implicit language resides in the body and the right hemisphere.

The relationship between the left hemisphere and the right approximates a relationship between reading and living, between a book and life. Life can have meaning without books, but books have no meaning apart from life. A book can enrich how one experiences life, but the book is never life itself. Books are a distilled, boundaried, frozen slice of life experienced. But now that the book is bound and on a shelf, it is dead until it is read and brings something new and creative to life through the reader.

“Life goes into books and books go back into life,” transforming life in the process. Think about all the life experiences that went into the writing of books, and how books, in turn, have had their part in creating the world we know.

All metaphors break down somewhere, but it illuminates something key to life in the hemispheres. The book is like life in the left hemisphere: A static, organized, categorized re-presentation of life. It has taken life in all its wild complexity and fluctuation and tried to freeze some kind of moment or pattern. Life in the right hemisphere is like life as it comes to us in a torrent of immediacy, and also as it emerges through reading a book.

Throughout the millennia, thinkers have commonly conceived of human history as a series of clashes between two opposing forces. Nietzsche used the Greek deities Apollo and Dionysos to personify the different drives, one force celebrating human ingenuity and creative order of the world, the other reveling in life’s incorrigible chaos. Freud wrote of life and death instincts. Jung mapped out his own history-influencing polarities. These forces are invisible, but their presence becomes evidenced during the long course of history’s ebbs and flows.

The relationship between the brain’s left and right hemispheres gives us fresh insights into historical processes. Obviously the human brain has remained a constant throughout history, and we have hints of which hemisphere was preeminent during which periods of Western history. Without reducing historical moments to a single factor, or saying laterality explains it all, we can see how the different hemispheric processes play out in the realms of society, politics, economics, and religion. We humans have always possessed brains, and depending on which hemisphere rules the cerebral roost at a current historical moment, the kinds of decisions and approaches to life can radically diverge. When the left hemisphere goes rogue and stops communicating with the right, that will manifest itself in all kinds of ways.

It would take reams and reams to do even partial justice to the effects of the interplay between the hemispheric brain and Western history, and far more still to track those connections across world history. But Western history, especially the past five centuries, reveals a growing reliance on left hemisphere processes—to the neglect and exclusion of the right hemisphere. The hemispheres have become disconnected and the right hemisphere, the master, historically the source of security and wisdom for humans, is being locked away. We have increasing trouble returning to it.

What would a world completely dominated by the left hemisphere look like? It would be a society lost in facts and the details of life, unable to consider the bigger picture of what it all means. Cosmic questions would not be entertained because they are too grand and irreducible. Scientists and thinkers in left hemisphere society would contemptuously brush aside such trivialities as unanswerable. People would care more about information than knowledge—and certainly more than wisdom, which would strike the left hemisphere society as too vague to pick apart or pin down a set of general rules and regulations.

Knowledge that came through embodied experience (instead of through documented paths of certification) would be viewed with suspicion or derisiveness—even though embodied experience in a skill has been considered the mark of expertise for most of human history.

Life would be thoroughly mechanical and bureaucratized, with a growing number of ventures under someone’s persnickety, paper-pushing thumb. More documentation, more people behind desks who report to people behind bigger desks. Life would be heavily documented and monitored, and to rationalize more bureaucracy, there would be yet another onslaught of paperwork.

The left hemisphere loves numbers because they allow us to measure quantity (not quality). They are predictable, safe, and easy to manipulate. It is in the world of what-ness rather than how-ness, where everything becomes an object rather than a subject—including other people. The individual is lost because uniqueness (a hallmark of right hemisphere processing) gets in the way of efficiency that the left hemisphere craves. It is easier to come up with broad, identifiable categories to sort large groups of people rather than to see people as individuals. Uniqueness gets in the way. Equality becomes an ideal, but a very abstract one. Moreover, equality comes to mean sameness and interchangeability, rather than individuals deserving of dignity and respect. People become treated like exchangeable (“equal”) parts in a machine and assessed in terms of productivity. A person would be viewed and valued according to machine-like criteria: How much can one do? How quickly? and How precisely?

Life and relationships would be more fragmented and abstract. People would spend more time in re-presentations and virtual life than life itself—with all its immediacy, risks, and unpredictable vicissitudes. Technological advancements would remove such inconveniences, but it would remove life lived in the process. The left hemisphere makes life manageable, but it is always life at a distance until the left hemisphere reconnects its small pool of “knowledge” to its master right hemisphere.

Does any of this sound eerily familiar? In many ways, this is the Western world in ever-increasing measure: A civilization trapped in the left hemisphere and dismissive of right hemisphere processes, a society trying to run ahead of life without realizing that life provides the ground needed to step anywhere in the first place. The left hemisphere has enabled the building of remarkable institutions and technologies. Civilization would not exist without it, but if the left hemisphere operates on its own without connecting with the master right hemisphere, civilizations have no soul, no meaning. They begin to collapse, just like ancient Greece and Rome.

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