Glossary · Cognition and analysis methods
Five whys
Also known as: 5 Whys, 5-why analysis, Five whys analysis
German: 5-Why-Methode
In quality management, the five whys is a questioning technique that asks “why?” repeatedly — typically about five times — to trace a problem from its symptom to an underlying cause; it was developed at Toyota and described by Taiichi Ohno as part of the Toyota Production System.
- Thinking models
- Problem solving
- Engineering
In one sentence
The five whys asks “why?” repeatedly to trace a problem from its symptom to an underlying cause, a technique from the Toyota Production System.
Example
Why did the operator skip the purge step? The step was on the next page. Why? The warning pushed it there. Why? The template puts all warnings first. The cause is the template, not the operator.
Explained in context
Context cards connect this term with others to answer one question. Also in British English and German.
How it applies
- Origin: The technique is credited to Toyota, where Sakichi Toyoda is often named as its originator; Taiichi Ohno described it in his book on the Toyota Production System as a way of reaching the real cause of a problem on the shop floor.
- Use: It is a quick entry point into root-cause analysis. Its limits are known: a single chain of answers can miss parallel causes, and it stops at what the people asking already know.
- Technical documentation: Asking "why" repeatedly about a user error often ends at the document — an unclear step, a misplaced warning, a template — rather than at the user.
Five whys vs. first principles thinking
The five whys looks backward from a symptom to its cause. First principles thinking looks downward from a problem to what is fundamentally true and then builds forward. Both start by refusing the first answer.