Categorizing a Continuum – Quadrune Mind

Paul MacLean, the Triune Brain, and the Necessity of Metaphor

“Thus, we’ve got the brain divided into three functional buckets, with the usual advantages and disadvantages of categorizing a continuum. The biggest disadvantage is how simplistic this is. Despite these drawbacks, which MacLean himself emphasized, this model will be a good organizing metaphor for us.” –Behave, Robert M. Sapolsky¹

Introduction

My original inspiration for the quadrune mind model of human nature and spiritual consciousness was the triune brain model developed in the mid-20^th century by neuroscientist Paul MacLean. His brain model was presented as a training tool for use by counselors at an outpatient alcohol counseling center where I was working at the time.

Over several months of educational sessions during 1984 and 1985, I came to appreciate how the “three-layer” brain could help me better understand the “mind” of an addicted person. For example, if a loved-one tries to stop an alcoholic from drinking, the alcoholic experiences this intervention as if their loved one is trying to keep them from breathing. This extremely intense reaction is driven by the “reptilian” brain’s sole purpose of ensuring our biological survival. However, this brain is not “rational” enough to know if what we truly need to survive is alcohol or air. As a result, the alcoholic may think the loved one is suffocating them by trying to keep them from alcohol, and it becomes either the alcohol or the loved one, whichever is more necessary for survival at the moment.

In 1997, I began to do professionally related presentations as an Oklahoma licensed psychologist. Because of my generalist’s approach to human behavior, consciousness, and the brain, my various continuing education classes were approved for continuing education credits by the licensing boards of a wide range of helping professions, including physicians, licensed professional counselors, psychologists, social workers, nurses, and, of course, drug and alcohol counselors.

In 2019, my daughter, Kerri, began developing a website, and in 2020 we published our first essays for the website, Quadrune Mind: A Neurospiritual Guide to a Purposeful Life. Since then, we’ve transitioned the model from an evolutionary approach to a developmental one, with a focus on the inherent spirituality of human nature. However, although we rely less on the triune brain and more on developmental stages, MacLean’s work remains a strong influence in the current model, and we believe there is good reason to keep him as our philosophy-of-mind-inspiration.

During the 1980s, MacLean’s triune brain model had reached its greatest influence professionally, and its highest popularity among the public. Since then, it has retained much popular appeal but has lost a substantial portion of its professional support. Current neuroscientists see the human brain as much more complex than MacLean’s triune brain model suggests. And evolutionary biologists have learned that the ancestral history of humanity is much more tangled than MacLean’s more linear description of the evolution of reptiles to mammals to primates to humans.

To me the rejection of MacLean and his model seems to be overly dismissive in tone.² It is as though MacLean had been revealed as a charlatan selling snake oil, or so naïve as to be almost childish in his simplistic views of neuroanatomy. The attacks on MacLean seem to emphasize the tri- part while ignoring the -une side of his triune brain model.

In other words, I believe MacLean’s critics see the world as a series of categories and therefore only understand his model as dividing the brain into three simplistic parts (which the growing emphasis on brain networks seems to contradict). But in doing so, they miss the bigger continuum. If we understand MacLean’s model—and the world in general—in terms of continuum, not category, suddenly the significance of the “une” becomes much more evident. We can have a triune brain and brain networks, because it is the connectionsamong brain regions that are essential to a fully-functioning brain. When it comes to the brain, the whole is most certainly greater than the sum of its parts.

Q: Which is More Real, Category or Continuum? A: Continuum

“[The founder of behaviorism, John] Watson was pathologically caught inside a bucket having to do with the environmental influences on development. ‘I’ll guarantee… to train him to become any type.’ Yet we are not all born the same, with the same potential, regardless of how we are trained.” –Behave, Robert M. Sapolsky³

Before proceeding, it would be helpful to have a clear definition of “category” and “continuum” so we can clearly see how seeing a model or existence through one will color every aspect of our experience of that model or existence. Fortunately, Merriam-Webster nearly always has the perfect definition.

Category: “any of several fundamental and distinct classes to which entities or concepts belong.”⁴

Continuum: “a coherent whole characterized as a collection, sequence, or progression of values or elements varying by minute degrees.”⁵

Both MacLean and his critics are in the business of categorizing the continuum. However, they may believe differently about how “real” the categories are. MacLean’s “reptilian” category of the human brain receives some of the most intense rejections for not being real.⁶ Critics cite the reductionist research that “proves” that there is no “reptilian” brain in the human head. But this does not address the phenomenologically obvious proof that actual human beings are quite capable of behaviors that are horrifyingly analogous to reptilian-like behavior; e. g., cold-blooded predation of other human beings and the silent patrolling of territory.

I believe that, like John Watson in the quotation above, MacLean’s “scientific” critics are more caught up in their reified categorical descriptions of the human brain than the philosophically-minded MacLean was when he created his triune brain model. In contrast to Watson’s belief that his own categories of learning were real and needless of further examination, Sapolsky gives very valuable examples of how to use categories strategically. He uses various neurological terms “simplistically” to convey the greatest amount of useful information while causing the fewest migraine headaches for learners along the way. He often reminds the reader of the vast complexity of brain structure and function down to the microscopic level of neurons, hormones, genes, etc., and their dizzyingly tangled interactions. Sapolsky knows the territory. However, once it is understood that the simpler terms are being used as a shorthand for what would otherwise be too cumbersome to be a useful model of a real-life brain, then the simplistic use of those words is not simple-mindedness, but a pedagogical necessity.

This is how I think MacLean meant his terms to be used. As Sapolsky said in the quotation that opened this essay, MacLean himself was very aware of the limitations of his terms to describe the human brain. But the triune brain model was, and still is, a “good organizing metaphor” for understanding how and why human beings can exhibit an incredible range of behaviors, clearly revealed to all of us. It is MacLean, who was able to keep in mind the complexity of the underlying continuum of the whole brain without becoming mired in the reductionists’ weeds.

In the following sections I describe, from the perspective of the quadrune mind model of human nature, how people dominated by various levels of consciousness perceive the world in relation to categories and continua.

In the first section, I describe how infants and young children experience their reality as consisting of two categories and zero continua. In the quadrune mind model that I developed with my daughter, Kerri, we discuss how we see this same level of consciousnesses in adults who are acting from their infantile mind because afflictions to the brain have dissociated the mind (in other words, turned the mind from a continuum into categories because it is not able to function properly as a holistic continuum).

The second section refers to the perceptual world of the adolescent, who can conceive many categories and many continua. It is also during early adolescence that the ability to understand and express metaphors becomes fully developed.⁷ This level of consciousness represents the rational, critical-thinking mind, which, for the past few hundred years, has been held as the highest possible level of cognitive capacity for human beings. It is also the level of consciousness we see in adults thinking with their adolescent mind.

The highest level of consciousness, which represents the quadrune mind model’s fully matured human nature, is described in the third section. This is the spiritual Grownup described in the quadrune mind model, who is capable of letting go of all categorical thinking and experiencing directly the one and only continuum that remains.

For Infants and Young Children (or the Infantile Mind in Adults):

Q: How Many Categories and Continua Are There? A: Two Categories, Zero Continua

At birth, only the most primitive part of our brain at the bottom of our skull is already fully functional. It has one task: to insure our biological survival. To do this, it divides the world of sensations into one of two categories: pleasant or unpleasant. The baby will approach things that are experienced as pleasant, such as suckling the breast for milk, but will withdraw from an unpleasant stimulus, such as very bright lights. The categories of “breast” and “lights” are not contained in any conceptual continuum by the infant—the infant does not think, “breast milk is my favorite, but formula, though less desirable, will also keep me alive,” or, “if they dim the lights, it would be much more pleasant.” The milk and the light each exist as respective examples of one or another thing⁸: pleasant or unpleasant with nothing in between.

Many adults also spend much of their lives in the same two-category, no continuum world of young children. The categories of the world are seen as concrete and discrete. Good and evil can be sorted out every day without any ambiguity. Friend and foe are distinct characters, if not species. National borders are sacrosanct. Heaven and Hell exist as truly as Earth as categorical destinations dividing humanity for eternity. The specific two categories may vary from culture to culture and person to person, but the dichotomies, whatever they are, can never be bridged.

For Adolescents (or the Adolescent Mind in Adults):

Q: How Many Categories and Continua Are There? A: Many Metaphorical Categories for a Complex World, Many Continua for Discerning Thinking

The map is not the territory. –Alfred Korzybski

A map is a physical metaphor.⁹ A model is a mental map. The model is not the territory.

Categorizing a continuum is required whenever we need to slice reality into small enough bites that we can chew. We do this by using metaphors. Metaphors allow us to combine different “kinds” of things into a single conceptualized continuum within our creative mind. This is true whether we are dividing the continuum of biological evolution, human development, maps, or food.

I don’t believe many scientists would demand that a map contain every detail of the territory it represents for it to be “true” or “real.” And what the map needs for it to be useful depends on how it is to be used.¹⁰

Whatever the mental map, or model, represents, it must always be judged upon its usefulness as a representation of reality; not in the fidelity of its reproduction of reality.¹¹ If MacLean’s triune brain model is good enough for the splendid Robert M. Sapolsky, it’s good enough for me.¹² In any case, we will always need categories to live everyday life. What really matters is if we create the categories for good or ill; whether categories are used to benefit life or destroy it.

For example, we can categorize the nature continuum for the purpose of taking shared joy in the gift of its multifaceted and rich beauty and abundance, or so that we can more easily divide it into personal property. The different reasons we create categories will lead to very different relationships with others and the environment. Categorizing human beings can help us conceptualize all of humanity as our very extended family for whom we must care, or see others as predators and competitors to our own personal survival. From the quadrune mind perspective, the way we categorize (subconsciously for our own survival, subconsciously for our family’s survival, rationally to create a rational world, or rationally in the paradoxical service of spirituality beyond rationality) reveals the level of our consciousness.¹³

Our ability to categorize what exists is truly unlimited. Even more, each “individual” continuum is part of a higher order continuum. The animal continuum is a subset of the life continuum; the human being continuum is a subset of the life continuum; the moral continuum is a subset of the life continuum; the hygiene continuum is a subset of the life continuum; and the life continuum is a subset of the existential continuum!

Consider A Shopping List for the Grocery Store

As an example of the necessity of balancing categories and continua to take purposeful action in the real world, consider this rather quaint scene: A mother is sending her young son to the grocery store to buy an item she needs for a recipe. The first category she says is, “Go to the store,” which categorizes the continuum of all places he might go, including offices, friends’ homes, etc. The next category: “Go the grocery store,” eliminating all other kinds of stores. Then, she might say, “Go to the grocery store and buy what I need for my recipe.” The child can now ignore all nonedible items and edible items, such as candy bars (perhaps to the boy’s chagrin), that she does not use in recipes. The child is then told to buy some berries, but which kind? She tells him to buy blueberries, organic, grown locally. These further categories discriminate each continuum of kinds of berries, how they were grown, and where they are grown, although the boy still may not know whether “locally grown” means in the state or from the nearby organic, regenerative locally owned farm.

After many of these errands for which the boy is sent to the grocery store to get his mother what she needs for the family meals, he begins to acquire a more sophisticated understanding of what she intends him to buy with less need of categorizing the continua of stores, specific items, and what kind of each product she wants him to get. At that point the mother can confidently use the simpler instruction for the boy to “go to the store and get what I need to cook dinner” without losing any of the finer levels of instructions.

For the Spiritually Minded Grownup:

Q: How Many Categories and Continua Are There? A: Zero Categories, One Continuum

I believe that behind every categorical difference of kind is a more subtle continuum of differences of degree. —Tom F. Shadid

The mystic of the one continuum has always known that all is connected to all. There is no Other. There are no borders. To experience the wholeness of all the categories of all continua is to be in a state of awe! As physical beings in a physical world, we really can’t live with zero categories all the time, and probably shouldn’t try to, if we are to be of any use during this lifetime. On the other hand, as adults, being stuck in the categories as the only reality, is to be separated from our own true Grownup human nature, each other, and the Organizing Universal Metaphor, which is the One Continuum, which is God.

QM and Paul MacLean’s Triune Brain Model

QM, Phylogenetic Regression, and Extreme Aggression

What Is It Like to Have a Mind?

QM as a Model of Human Consciousness

Sapolsky, R. M. (2017). Behave: The biology of humans at our best and worst. New York: Penguin Books. [Emphasis added. P. 23].
For example, “triune.” Merriam-Webster.com Dictionary, Merriam-Webster. Accessed 6 Jan. 2026. “Recent Examples on the Web: The triune brain model, developed in the mid-20th century by neuroscientist Paul MacLean, has long been considered nonsense by most neuroscientists; the theory was first disproved back in the 1970s.—Kristen Martin, Washington Post, 2 Aug. 2023” [This is an example of popular culture’s simplistic total rejection of MacLean’s model. Nevertheless, I believe it can be used as a powerfully useful metaphor for philosophy of mind or as a new model of human nature].
Sapolsky, R. M. (2017). Behave: The biology of humans at our best and worst. New York: Penguin Books. [P. 9].
[This quotation indicates that John Watson took the behaviorists’ categories to be absolutely real, the way things really are. For him there is no continuum between physical behaviors and mental processes in animals or humans. I believe that Watson’s essentially dogmatic rejection of a continuum between “nurture” and “nature,” as co-determinants of human development, is the “pathological” point of Sapolsky’s comment].
See “category” Merriam-Webster.com Dictionary, Merriam-Webster. Accessed 26 Jan. 2026.
See “continuum” Merriam-Webster.com Dictionary, Merriam-Webster. Accessed 26 Jan. 2026.
Wills, M. (2025, April 11). The reptilian renaissance: Think reptiles like crocodiles and caimans are slow learners? It’s probably because you’re human. JSTOR Daily. “These aren’t your grandfather’s reptiles.

“There’s even some evidence of reptilian tool-use: species of crocodiles and alligators ‘display sticks and twigs on their snout in order to lure nest-building birds.’ This has only been observed in bird-breeding season, when the birds on the lookout for sticks to construct or repair their nests.

“Once considered simple and ‘primitive,’ the ‘reptilian brain is now recognized to govern complex behaviours,’ write De Meester and Baeckens. They argue that reptiles show ‘immense potential’ as model species for research into the ‘mechanisms, the development, and evolution of animal cognition.’

“Clearly, there’s a lot more to be learned about lizards, snakes, turtles, and crocs. As always when it comes to evolution, this also means discovering more about ourselves, for we share a common ancestry with reptiles. In fact, all vertebrate brains share the same basic ingredients, differing in the number and arrangements of neurons.

“In the 1960s and 1970s, the concept of the ‘reptilian brain’ as the foundation of a triune human brain system became so popular it still inflects the discourse even though neuroscience has moved well beyond that simplification. The human brain doesn’t have a ‘primitive’ part at its base; there’s no lizard amygdala controlling our flight or fight reflexes. The idea, however, continues to have pull, likely because it’s so easy to understand—and provides a scapegoat, in the lizard-made-me-do-it excuse—than the actual complex interactions of brain networks.

“And now we know that characterizing actual lizards and other reptiles as being primitive when it comes to cognition is another simplification.”

[Emphasis added. Hyperlinks have been removed from the original. This recent article presents an interesting complication to the discussion of brain evolution. I think for MacLean, it would be the commonality of our ancestry with reptiles and mammals, which need not be linear, that gives credence to the triune model as a metaphorical organizing principle of human behavior, which is how Sapolsky uses MacLean’s model].
For more information about metaphors, see Kalandadze, T., Tonini, E., & Bambini, V. (2021, December 22). When dancers are butterflies: How the brain understands metaphors. Frontiers for Young Minds. “Imagine that a friend of yours, Sarah, is talking about a ballet and says, ‘Those dancers are butterflies!’… The magic of metaphors is that they can communicate a lot of information with just a few words. The mental images metaphors create provide more information faster than when someone describes something with a literal sentence, that is, a sentence in which words are used only in the way they are defined in the dictionary. With a metaphor, Sarah communicates more details than simply saying that the dancers are nice. For instance, the butterfly metaphor tells us that the dancers’ movements are so elegant and delicate that they resemble those of butterflies. Metaphors have a sort of superpower compared to literal expressions, as they allow us to say more than our words mean.

“Metaphors can also be helpful when talking about things that are difficult to explain, such as feelings, emotions, or complex scientific ideas.” [The authors describe techniques, such as “thinking maps,” to help people who have difficulty understanding metaphors; for example, people with autism spectrum disorder. A helpful Glossary of basic relevant terms is also provided].
See “thing” Merriam-Webster.com Dictionary, Merriam-Webster. Accessed 13 Jan. 2026. “1 : an object or entity not precisely designated or capable of being designated

use this thing.
Gibson, S. (2020, November 29). Maps are metaphors. Medium. “Maps can define our surroundings, define who is in charge of the land, explain how to get from point a to point b, or simply convey what we can do or not do…

“Maps served a metaphorical function of defining our world for political purposes and navigation. We used maps to represent the real world, and maps limited what we could imagine and describe…

“Maps have historically been a driving force in how we understand the world. How we set up the maps and present the maps reveals our bias and beliefs about our power. A map containing marked borders dictates political separation and nations. Maps can demonstrate who belongs with who, and who is persona non grata.”
Some uses for various maps include: political maps depict political boundaries and capitals; physical maps display the natural landscape features of the Earth; topographic maps portray the Earth’s three-dimensional landscape on a two-dimensional medium; weather maps provide a snapshot of atmospheric conditions at a specific time and location; and geologic maps illustrate the Earth’s geological diversity, portraying rock types and geological periods that shaped a region.
See my essay, QM and Paul MacLean’s Triune Brain Model, for my use of George E. P. Box’s quotation, “Remember that all models are wrong; the practical question is how wrong do they have to be to not be useful.”
Of course, my statement here does not mean that I necessarily believe Sapolsky would endorse my applications of MacLean’s model, should he ever come upon them.
See QM as a Model of Human Consciousness for additional information.