Do You Know What I Know?: Celebrating the Career of Henry M. Wellman

Henry M. Wellman, the Harold W. Stevenson Collegiate Professor Emeritus of Psychology, is known to friends and colleagues for many things. Among them are his always-on ironic sense of humor, his voluminous handwritten feedback on manuscripts, and his insistence on commuting by bicycle regardless of weather. But he is also known as one of the most prominent developmental psychologists of his generation, as well as a generous mentor who has launched the careers of dozens of other scientists.

As a researcher, Wellman studies children’s Theory of Mind (ToM)—how children come to understand their own and others' knowledge, beliefs, desires, intentions, and emotions. This capacity emerges early in childhood and underlies much of what makes our species distinctive, including pretend play and the ability to lie. For the past 40 years, Wellman has been the most prominent researcher studying these issues. His research has examined questions that include: What are the components and structure of these belief systems? In what sense do they constitute a theory? What changes and what is constant throughout development? How does ToM develop across different cultures? What are the brain bases of ToM in young children?

Our understanding of how ToM develops is one of the greatest success stories in recent psychological research. Indeed, ToM is one of the rare psychological concepts with such compelling explanatory power that it appears in every introductory psychology textbook. The textbook definition typically goes something like this: babies and very young children can struggle to distinguish their own minds and experiences from those of others; they often assume that other people see what they see and know what they know. But as children develop, they come to understand that other people have minds that are separate and different from their own—that each person has differing knowledge, experiences, and desires—and those different minds are what drive people’s behaviors. 

Many textbooks also mention a particular moment in ToM development: a child’s realization that other people’s beliefs (and even the child’s own beliefs) can be false or incomplete and that others cannot see inside the child’s own thoughts to know what he or she knows. That milestone is important in part because it is what allows children to learn deception. After all, I cannot understand how (or even why) to lie to you until I understand that your knowledge of the world is limited (sometimes downright wrong), and that I can inform you about the world (and so do falsely).

Wellman has been a foundational thinker in ToM research since its inception in the early 1980s. But to understand many of his contributions, one must dig a bit deeper than those sketchy textbook passages. For understanding Wellman’s work, one of the most important of those questions is this: Why is it called theory of mind? Is that just a catchy phrase? Wouldn’t knowledge of mind or understanding of mind be more appropriate?

Well, no, at least not according to Wellman and other proponents of the so-called theory-theory—that is, the theory that ToM really is a theory. Throughout his career, Wellman has posited that children develop ToM using essentially the same neurocognitive processes adults use when developing other theories about how the world works. Those processes include the three “Es”: exploration, experimentation, and explanation. Indeed, one of Wellman’s greatest contributions to developmental psychology could be summed up as the idea that children’s theory of mind is a naïve theory children develop to explain the social world of people. In Wellman’s model, children’s theories are not static; children create and revise their theories over time as they attain new knowledge, in a process somewhat similar to the way scientific theories develop. That similarity has led some Wellman-inspired theoretical frameworks to be called “child scientist” models, though Wellman is careful to point out the limitations of this analogy and turn it on its head by saying, “It’s not so much that children are little scientists as that scientists are big children.”

In fact, it was partly Wellman’s fascination with the similarities between children’s naïve theories and other kinds of theories that first led him to developmental psychology. During our interview, he cited a particularly memorable childhood theory he encountered while working as a Minnesota preschool teacher in the early 1970s. One summer, he was helping a four-year-old boy put his shoes on when he idly remarked that the child was going to need new shows soon because his feet were getting so big. 

The boy’s response took Wellman off-guard: “He looked at me and said, ‘No, your feet never get any bigger,’” Wellman recalls. “So I asked him how that works, and he said, ‘Well, you drink your milk, and it goes down to your belly, and it comes out in your pee.’ Essentially, ‘It never gets to your feet, so they can’t ever get bigger.’ That really struck me because—although completely incorrect—it’s such a sensible idea that is based on a kind of theory about nutrition he had developed on his own. He understood that we need food to provide energy and make us grow. But not knowing anything about blood circulation or the like, he came up with this idea that food directly contacts parts of the body to make them grow. In its own way, it was a coherent explanatory theory based on the evidence available to him. When scientists come up with coherent explanations based on their explorations of the world, we call them theories. These childhood understandings—and many adult ones too—are, I believe, ‘theories’ as well. Not scientific theories but naïve theories. And they fascinate me. When David Premack and Guy Woodruff came up with the term theory of mind in the late 1970s, a lot of people liked it as a catchy title. But I said, ‘No, children’s theory of mind really is a theory.’”

Wellman explains that his work over the decades has provided evidence supporting the theory-theory in various ways. “Children’s theory of mind promotes exploration—finding out what others do and do not know. It promotes explanation—why did mom go to her purse for the car keys when they are on the table? She thought they were in her purse. It promotes exploitation—I can deceive you by lying to you.” 

Scientific theories develop; they change as evidence accumulates. “So too does childhood theory of mind” says Wellman. “That’s part of its fascinating story.” 

But what does the process of ToM development look like in practice? Wellman and his collaborators have developed a scale to track children’s progress in developing ToM. The scale defines and tracks children’s attainment of several important conceptual milestones. Those milestones, in order of development, are as follows:

1. Diverse Desires: Children realize that other people can have different desires about the same object. For example, “I like apples, but you don’t.”

2. Diverse Beliefs: Children realize that people can believe different things about the same object when the child themself does not know which answer is true. For example, “I think my lost book is at home; Dad thinks it’s at school.”

3. Knowledge Access: Children learn that people can know things that other people do not know. For example, “I know the remote is on the couch, but Mom doesn’t know where it is.”

4. False Belief: A child is able to understand that someone is not only ignorant but has a decidedly incorrect belief. For example, “There are crayons in the bandaid box, but my teacher thinks it has bandaids.”

5. Hidden Emotion: A child understands that the emotions people display externally can be false or may disguise what they actually feel. For example, “Jane hates the scarf her grandmother gave her, but she says she smiles and says she loves it.”

Although the exact age at which children reach the milestones varies, the order in which they reach them is relatively invariant. The pattern follows a mostly consistent, linear pattern because each major milestone appears to be a prerequisite for the next.

Interestingly, however, sizable variations in the rates at which children attain the milestones do exist. For example, research conducted by Wellman and his collaborators has shown that Deaf children raised in non-Deaf families tend to reach the milestones much later than hearing children raised in hearing families (and 95% of deaf children are born to hearing parents). But intriguingly, Deaf children raised in Deaf families (or in families that make extensive use of sign language) attain the milestones at the same rate as hearing children. It has long been suspected by theory-theorists that exposure to conversation and vocabulary concerning emotions and beliefs helps children more readily grasp concepts critical to developing ToM, and Wellman believes the differences seen among those groups provide definite evidence in support of that hypothesis. Moreover, other studies conducted by Wellman and his collaborators have shown a positive correlation between the rate at which children develop ToM and their performance in school, particularly in elementary and middle school. Among other implications, this suggests that exposing young children to rich conversations and language about feelings and beliefs—whether that language is spoken or signed—may help children achieve ToM more quickly and ultimately perform better in school and later in life. 

But Wellman is known for more than just his trailblazing contributions to understanding ToM. His collaborations—and especially his mentorship of students and junior faculty—have also had a tremendous impact on the field. To honor that impact, he has received major mentoring awards from both the American Psychological Association (APA) and the Association for Psychological Science (APS).