Have you ever pictured a child who has just received a toy hammer wandering around the house, tapping the corners of tables, the legs of chairs and even the lids of pots? Adults are not so different: once we master one method, even unfamiliar problems start to look like problems that method can solve. This tendency is called the “Law of the Instrument.”
Put simply, the Law of the Instrument means “the phenomenon in which the tools we have decide how we see a problem.” American philosopher Abraham Kaplan introduced it under this name in a 1962 talk, and because psychologist Abraham Maslow popularized it in 1966 with the image of a hammer and nails, it is also known as “Maslow’s Hammer.”
In this article, we will look in turn at the history of the hammer-and-nail metaphor, the mechanism by which familiar methods hold our thinking in place, examples found across work and society, and finally ways to avoid being trapped by a single hammer.
The Tool in Your Hand Shapes the Problem: The Law of the Instrument
1. The History of the Hammer-and-Nail Metaphor
The saying that everything looks like a nail to a person holding a hammer is used today like a proverb, but it actually took its present form through the writings of several people.
(1) The Boy with a Hammer
In 1868, the London magazine Once a Week published a piece observing that if you give a boy a hammer and chisel and show him how to use them, he immediately begins to hack at the doorposts.
(2) Kaplan’s Law of the Instrument
At a February 1962 meeting of the American Educational Research Association, Kaplan stated the law, “Give a boy a hammer and everything he meets has to be pounded,” and left a similar sentence in his 1964 book The Conduct of Inquiry. He pointed out that scientists, too, tend to frame problems so that they require the techniques they already know well.
(3) Maslow’s Hammer
In The Psychology of Science (1966), Maslow told the story of an automatic car wash that treats whatever goes into it as a car to be washed, and then wrote that if the only tool you have is a hammer, it is tempting to treat everything as if it were a nail. The line is often attributed to Mark Twain, but quotation researcher Ralph Keyes stated that there is no evidence whatsoever for this.
2. How Familiar Methods Hold Our Thinking in Place
The Law of the Instrument stems less from laziness than from the way the brain works. A method that has succeeded once comes to mind first, and the more often it has worked, the less we feel the need to look for another path.
- Law of the Instrument: The tendency to rely too heavily on one familiar tool or method and try to solve every problem with it.
- Golden Hammer: A term in software for the faulty pattern of stubbornly applying one familiar technology to many different problems.
- Functional Fixedness: The phenomenon of seeing an object only in terms of its usual purpose and failing to think of other uses.
- Déformation Professionnelle: A French expression for the tendency to see the world only from the perspective of one’s own profession.
(1) Luchins’ Water Jar Experiment
In 1942, American psychologist Abraham Luchins gave people problems in which they had to measure out a set amount of water using three jars of different sizes. For example, to measure 100 units with jars of 21, 127 and 3 units, you have to fill the large jar and then pour off water with the smaller ones. People who practiced this long method mostly kept using it even when a problem could be solved simply with just two jars, while almost everyone who solved the problems without practice found the simple method. This is called the “Einstellung Effect.”
(2) Rewriting the Problem to Fit the Tool
Kaplan believed that people tend to define problems in a shape that can be solved with what they already have. Instead of seeing the problem as it is, we magnify the parts our tool handles well and shrink the parts it does not fit.
(3) The Urge to Use Skills We Have Learned
In 1984, investor Warren Buffett criticized academics for applying unsuitable mathematics to the study of financial markets, remarking that skills acquired with great effort feel wasteful to leave unused, even when they serve no purpose.
3. Hammers Throughout Work and Society
The Law of the Instrument goes beyond personal habit and also influences decisions made by organizations and societies.
(1) The Golden Hammer in Software
The 1998 book AntiPatterns described the obsessive application of one familiar technology or concept to many software problems as an anti-pattern called the “golden hammer.” A typical case is carrying a well-known language or database into a new project with entirely different needs.
(2) The Law of Irresistible Use
In 1967, Lee Loevinger, a commissioner of the U.S. Federal Communications Commission (FCC), applied this idea to government and called it the “law of irresistible use.” He observed that the very existence of a government agency is treated as proof that something needs regulating.
(3) The Opposite When You Lack a Hammer
In his 2003 book Of Paradise and Power, American historian Robert Kagan proposed a corollary: when you do not have a hammer, you do not want anything to look like a nail. He used this idea to explain the different views of the United States and Europe on the use of military force after World War II.
4. How to Avoid Being Trapped by a Single Hammer
Escaping the Law of the Instrument does not mean throwing away familiar tools. A tool you handle well is a great strength; what matters is the habit of checking once more whether it fits the problem at hand.
(1) Write Down the Problem First
Before thinking of a solution, first write down what the problem is and what state would count as solved. Defining the problem apart from the tool reduces the temptation to bend the problem to fit the tool.
(2) Expand Your Toolbox
Learning new methods little by little increases the options you can choose from. In Luchins’ experiment, too, more than half of the people who heard the warning “Don’t be blind” found the simplest method on the later problems.
(3) Borrow the Eyes of Other Fields
Explain the same problem to people from other fields and ask how they would solve it. A path you could not see may be obvious to someone who holds a different tool.
The Law of the Instrument is not a claim that tools are bad, but a warning that tools can quietly set the limits of our thinking. When you meet a new problem, the simple thought, “Is the hammer in my hand the right tool for this problem?”, is the first step toward understanding the Law of the Instrument.
