The Thomas Theorem

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Practical Psychology

Why do you stop your car at a red light? How do you know what to say when you sit down at a restaurant? Why do some people have such a hard time accepting LBGTQ folks? There is one idea in sociology that can answer all of these questions, and a lot of questions about social interaction: The Thomas Theorem. 

The Thomas Theorem is a basic, but wildly complicated idea. And the history behind who we credit for the Thomas Theorem just proves how significant this theorem is in today’s world. If you have ever stepped back and wondered just why humans follow the rituals we follow, treat some people one way and other people another way, or had questions about the “rules” we all abide by, this page may satisfy some of your curiosity. 

What Is the Thomas Theorem? 

The Thomas Theorem states, “If men define situations as real, they are real in their consequences.” This idea first appeared in the 1928 book The Child of America, co-authored by W. I. Thomas and Dorothy Swaine Thomas. W. I. Thomas most often gets credit for this theorem, further proving their point.

Let’s break this theorem down. 

How Do We Define Situations As Real? 

What is real? Take a walk outside and look at what is around you. Do you see a tree? Is it real? The object in front of you might be real, as you can touch the rough texture with your hands and see its leaves with your eyes. But the idea of a “tree” is real only because society says it is. Society’s definition of a tree is what makes it a tree. Otherwise, you could point to what we know as a tree and say, “this is a duck.” Society has defined what a duck is, what a tree is, and the differences between the two.  

Over time, “man” has defined a tree as “real.”

What Are the Real Consequences of Our Situation? 

What would happen if you walked up to a stranger, pointed at a tree, and said, “this is a duck?” Well, they probably wouldn’t agree with you. They might look for a duck in the tree. They might agree with you only to end the conversation and get far away from you. Or, you might just find yourself in an argument with someone over whether a tree is a tree or a tree is a duck. That’s a real consequence of the situation “man” has created. 

Rules surrounding that tree may also affect how we interact with the tree. Let’s say you go up to the tree and chop it down with an ax. Or, you attempt to. Before you can actually chop the tree down, a neighbor whose house sits next to the tree comes out to yell at you. 

“This is my tree!” they say. “It’s on my property!” 

Your neighbor’s property lines are real because “man” has created a system that sells land as property. The neighborhood surrounding that tree, and any other relevant governing bodies, have mapped out the property lines. Their authority is “real” because “man” has deemed them to be the authorities. We follow authorities like governing bodies because man has created rules for interacting with different groups and the rules they create, from presidents to legislators to neighbors to friends. 

“Nothing” is stopping you from chopping down a neighbor’s tree, but because of all these “real” concepts and rules that society has created, the consequences of your situation will be real, too. You may be fined, thrown in jail, or forcefully removed from the property. If you claim that you’re just chopping down a duck, you may be sent to a mental health facility. This is how real the consequences of society are. 

How the Thomas Theorem Impacted the Creators of the Thomas Theorem

Dorothy Swaine Thomas was the first female President of the American Sociological Association. She was also a fellow of the American Statistical Association and the President of the Population Association of America. Though she co-authored the book that first mentioned the Thomas Theorem, she was not mentioned as a creator of the theorem until many decades later. Why? The Thomas Theorem can explain. 

The idea of a “woman” and a “man” are social constructs. In most societies throughout history, “Man” has decided that women have certain genitalia and men have certain genitalia. The idea that genitalia must stay the same throughout the course of a person’s life or that genitalia defines a person’s role in society is a “real” situation that has significantly affected our society. A person with certain genitalia, for example, could not have a credit card unless a person of differing genitalia co-signed on their application, until the 1970s. Credit and the law that changed how women could apply for credit (the Equal Credit Opportunity Act of 1974) are also social constructs. 

A person’s genitalia largely impacts the expectations that society, a social construct itself, has on the person. Who is expected to stay home and care for the children? Who is expected to go get a Ph.D. and make great discoveries? When you think of a person with the name “Thomas,” first or last name, do you picture what society has deemed a “man” or a “woman?” 

The idea of a woman’s role in society has evolved, but the consequences of old views and expectations still make an impact today. Women are still paid less than men. Women make up less than 30% of Congress. Think about your family. If your parents get sick, which of your siblings will be expected to care for them? 

Types of Social Constructs 

Gender is just one social construct that makes a huge impact on our world today. Other social constructs make a similar impact, but they have been so widely accepted as “real” that we don’t even think of them as social constructs. The consequences of these social constructs affect how we live our lives every day. 


What separates this page from a work of art that you can view with a quick Google search? Why is a urinal displayed in a museum, considered art, when other urinals are considered objects where we dispose of our urine? When Banksy’s painting was shredded at an auction, why was it still considered art (and why did it go up in value?) Art is a social construct, often commenting on the consequences of social constructs. Meta!


Why does a person’s skin color, or the amount of melanin in their skin, have such an impact on how society expects them to behave? Why is it that a person with more melanin in their skin will likely receive a lower appraisal for their house than a person with less melanin? Race is a social construct; our society has defined what classifies someone as Black, white, Hispanic, etc. The consequences of what makes someone a certain race have had significant effects, and not just in the days of slavery or Jim Crow. 

Traditions and Rituals

Why do we sing the National Anthem before sports games? How does everyone seem to know what a “traditional marriage” and a traditional wedding ceremony look like? Why is it normal for families to engage in prayer to begin a meal? All of these traditions and rituals, and the existence of traditions and rituals, are social constructs. The world will not end if a baseball game doesn’t begin with a National Anthem, but there will likely be consequences if this tradition is forgotten. 

Even though we as individuals did not create these social constructs, we uphold them. And because society as a whole continues to uphold them and deem them as “real,” the consequences of them remain real. This is how we know The Thomas Theorem to be true.

Reference this article:

Practical Psychology. (2022, November). The Thomas Theorem. Retrieved from

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