Left-brain versus right-brain ethics

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NPR science correspondent Shankar Vedantam hosts an excellent podcast entitled Hidden Brain, focusing on the science of human behavior. A recent episode features brain researcher and psychiatrist Iain McGilchrist, author of a book that tries to sort the myths from the science regarding the differences between our “left brain” and “right brain.” The two brain hemispheres sometimes appear complementary or mirrors of one another, yet at other times they seem to be locked in conflict.

Much of popular culture’s view of left brain versus right brain differences McGilchrist sees as unsupported by science, but in this podcast episode he does touch on a documented difference between the hemispheres corresponding to a view on ethical decision-making that I presented in my “Good People Disagree” series from last year. In short, McGilchrist sees goal-oriented ethical decision-making as mostly evaluated by the left side of the brain, while the “big picture” ethical considerations are primarily the domain of the right brain. So, how does he document this difference?

McGilchrist presents much of his research in his book Master and His Emissary: The Divided Brain and the Making Of The Western World, and this view of left-versus-right ethical decision-making is consistent with that thesis. [1] The “big picture” right brain usually functions as what he calls “the Master,” while the left brain processes the details perceived from the outside word through the sensory organs, or what he calls “the Emissary” role.

McGilchrist takes a similar approach to brain research as did the late Oliver Sacks, mostly by examining and following up on case studies of people who have incurred some sort of brain damage due to stroke, tumor, injury or other impairment. By examining functions lost and functions retained by these people, we get clues into the normal partitioning of the brain. This is also consistent with neuroscientist/philosopher Daniel Dennett’s view of the brain as a “probability evaluation engine,” an evolved, multi-function organ for processing sensory input, plus recalled memories, and evaluating the odds of the best decision paths for survival and procreation of the species.

It always needs to be said that this is not so much by intent or design as it is by millions of years of incremental math. Tiny probabilistic improvements in the chances for survival and procreation over this kind of time mean that these incremental improvements to the brain also tend to propagate.

The ethics of intention versus the end achieved

One of McGilchrist’s tests investigates how a person with damage to one or the other hemispheres, usually from stroke, evaluates an ethical dilemma designed to parse out end-based utilitarian thinking from a more “meta-ethics” evaluation of “the big picture.” The test asks, given these two scenarios, “Who is the most unethical?”

  1. A woman tries to poison the tea of her friend by putting poison in the tea, but she mistakenly puts in sugar instead.
  2. A woman intends to put sugar in her friend’s tea, but inadvertently puts in poison instead.

McGilchrist’s research indicates multiple instances where a person who has sustained a right-brain stroke, serious enough to cause impairment but leaving the left hemisphere unharmed, often sees the second woman as the more unethical, because in the end her friend was harmed. In the reverse situation, however, a person with a left-brain stroke can have severe trouble in evaluating detail, yet still perceive that it was the intent of the first woman that made her the more unethical, even though she was unsuccessful.

The suggestion here is that utilitarian thinking, a major “vector” of classic philosophical and theological ethical theory, while not necessarily confined to the detail-oriented left brain, nonetheless finds much of its decision-making volition there, while “big picture” meta-ethical thinking, or at least the part of end-based reasoning that considers the larger, more complex concept of intention, has a much stronger presence in the right hemisphere of the brain.

Implications for the “moral conversation”

My primary approach to ethics is what I call the “moral conversation” that has continued for many thousands of years among people seeking to live together in society. The earliest conversations were in “God languages” invoking the supernatural and preceding more formal theologies, and that language still speaks loudly in this conversation today. “Philosopher language” emerged as a non-religious alternative, and in addition to its formal speakers over the decades, we hear it in the arts and popular culture. Finally, scientists and mathematicians add their own languages based on rationality, observation and testing.

The narrow utilitarianism of parts of the left brain and “bigger picture” right brain, as noted by Iain McGilchrist, are joined by other evolved brain regions across both hemispheres to create the (at least) “four ethical brains” that we use in daily in this conversation. The conversation goes around and around inside our own heads as well as with our neighbors, as we seek to make moral and ethical decisions that will determine if we can indeed still live together in society. [2]

As long as we are talking, we are not fighting. And somewhere in that discussion, attitudes and viewpoints are changed, one by one. Sometimes that viewpoint change seems to move us into an anti-society direction, and that stress seems to hit my Twitter feed daily.


  1. Mcgilchrist, Iain. Master and His Emissary: The Divided Brain and the Making Of The Western World. Yale University Press, 2019.
  2. Here is my distinction between morality and ethics.

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