There is only one core issue for all psychology. Where is the "me”? Where does the “me” begin? Where does the ‘me’ stop”? Where does the ‘other’ begin?” So observed the late psychologist James Hillman.

This question is fundamental not just for individuals but for the societies they compose. We see lines being drawn every day—between self and other, us and them—in fields as disparate as politics, religion, science, art, music, language, ethics, law and entertainment. Whether it’s fierce disagreement over building a wall to keep out illegal immigrants, recognizing and accommodating transgender people, or the appropriateness of “edgy” humor or “boundary pushing” fashions, we continuously grapple with where to set limits.

What’s considered right or wrong, moral or immoral, understandable or outrageous isn’t defined as much by external authorities as by each one of us based on our personal sense of me/not me. The extent to which that line is fixed or permeable offers a fascinating vantage point on individual differences, as well as differences between contending groups and schools of thought.


A self requires a boundary. Even the most primitive creatures have a physical boundary (skin or another form of membrane) to discriminate “in here” from “out there.” The separation allows sensory stimuli to be processed, nutrients to be taken in and waste products to be discharged. Such a boundary literally defines the individual.

Through the development of nervous systems over the eons, some animals became capable of assessing what was happening to them in a more sophisticated way and determining what was to be done about it (approach, avoid, chase, etc.). Brains gradually emerged through this ongoing, sensory-based assessment of environmental interactions.

As individual selves, we become conscious of our own existence. We notice what is happening to us, but we do much more—we feel something about it, think about it, remember, plan, dream, imagine, create, all with our minds exploring real or represented environments. Because we are bounded within our bodies, we’ve ultimately come to have distinct minds and personalities.


A fascinating way of looking at personality differences revolves around this very concept of boundaries. The late psychiatrist Ernest Hartmann asserted that each person can be characterized on a boundary spectrum ranging from “thick” to “thin.” In his words:

“There are people who strike us as very solid and well organized; they keep everything in its place. They are well defended. They seem rigid, even armored; we sometimes speak of them as ‘thick-skinned.’ Such people, in my view, have very thick boundaries. At the other extreme are people who are especially sensitive, open, or vulnerable. In their minds, things are relatively fluid.… Such people have particularly thin boundaries…. I propose thick and thin boundaries as a broad way of looking at individual differences.”

Hartmann came to his conception in an interesting way. In the 1980s, he was studying people who have nightmares and noticed that they could readily recall other vivid or colorful dreams even if these didn’t qualify as nightmares. Such people seemed to him especially “sensitive,” “vulnerable,” or “imaginative” in contrast with others who came across as more “solid,” “stoic” or “persevering.” He suspected there are real neurobiological differences between thin and thick boundary people, and developed his Boundary Questionnaire (BQ) to gain more insight.

Since the 1980s, at least 5,000 people have taken the BQ, and more than 100 published papers have referenced it. The scores distribute in a Bell-shaped curve. Women tend to score significantly thinner than men, and older people tend to score somewhat thicker than younger people. Certain professions also seem to attract people of differing boundary type. Thin-scoring people predominate among artists, musicians, and fashion models, whereas thick-scoring people are more commonly naval officers, salespeople and lawyers.


More recent researcher has explored similar terrain. Psychologist Elaine Aron has examined various facets of what she calls the “highly sensitive person” or HSP. Harvard professors Jerome Kagan and Nancy Snidman have pointed up the differences between “high reactive” and “low reactive” individuals. Developmental psychologist Bruce Ellis and pediatrician Thomas Boyce have differentiated “orchid” children from “dandelion” kids (the former are highly sensitive; the latter are more numerous and more hardy). And author Susan Cain touched a nerve with her popular book Quiet, extolling the underappreciated virtues of the introspective personality. Taken together, such investigations indicate a rising degree of interest in the biological basis of key individual differences.


Boundaries are more than a measure of introversion or extroversion, openness or closed-mindedness, agreeableness or hostility, or any other personality trait. While boundary thinness has been found to correlate strongly with openness to experience (one of the Big Five personality dimensions), Hartmann and his colleagues considered boundaries to be a broader measure—and more interesting and useful for that reason.

Boundaries allow for an assessment of the characteristic way anyone operates in the world. To what extent are stimuli kept out or let in? To what degree is a person rigid versus flexible, impassive versus excitable, self-contained versus sensitive, closed versus open?

Such terms inevitably invoke sentience, i.e., the felt basis of self. Although Descartes opined “I think, therefore I am,” the contemporary scientific view is Sentio, ergo sum: I feel, therefore I am. Since consciousness derives from the having of sensations, and since sensation would be impossible absent a demarcated body, self must be based in feeling.


This approach is consistent with the work of neuroscientists and evolutionary psychologists such as Antonio Damasio and Nicholas Humphrey, as well as social psychologists such as Jonathan Haidt (The Righteous Mind) and Drew Westen (The Political Brain). The latter two explain how moral judgments and political preferences stem from an emotional core, as well as factors such as one’s embrace of order, the inclination to view others as similar versus different from oneself, and even the intensity of one’s sense of disgust (those who feel disgusted more easily tend toward conservatism).

Disgust offers compelling insight into the thick boundary/thin boundary dichotomy. At bottom, disgust is an involuntary reaction aimed at quickly and efficiently distancing oneself from a poisonous, unsafe or unsavory “other.” Someone whose boundaries are relatively thick will be more likely to notice and react to what is unfamiliar (and therefore suspicious), whereas someone with thin boundaries will be more likely to notice what may be similar between him/herself and others. Unsurprisingly, perhaps, numerous studies have drawn a correlation between germophobia and xenophobia.


People inevitably consider their own boundary type desirable and tend to disparage qualities associated with the other type. Thin boundary people may see themselves as “exciting,” “creative” and “innovative” but look upon those with thick boundaries as “dull,” “rigid” and “unimaginative.” Thick boundary people, on the other hand, may view themselves as “solid,” “reliable” and "persevering” while considering those with thin boundaries as “flaky,” “out there” and “unreliable.”

These differences suffuse every aspect of society, affecting perceptions of what is legal, just, worthwhile, artistic, funny, desirable, etc. People hardly ever realize the tremendous influence exerted by their own underlying sense of self. In that, most of us wear blinders. We would do well to embrace a bit of wisdom that comes with maturity, as expressed by that keen observer of people and relationships, Billy Joel:

Shades of grey wherever I go
The more I find out the less that I know
Aint no rainbows shining on me
Shades of grey are the colors I see

Note: Readers interested in learning more about boundaries are referred to Ernest Hartmann’s book Boundaries: A New Way to Look at the World (Summerland, California: CIRCC EverPress, 2011). An encompassing view of his work is available at