The Five Whys

The Five Why is a question asking method for getting at the root cause of a problem.  The method involves asking the question Why? five (or more) times until the root cause is revealed, and the problem can then be resolved.

The following example demonstrates the basic technique:

• My air conditioner does not work. (the problem)

1. Why? The unit blows air, it is not cold.
2. Why? The compressor seems to run, but it is not effective.
3. Why? There is probably not enough refrigerant in the system.
4. Why? I have not had the unit serviced in several years.
5. Why? I did not think of having it serviced when it was working.

• I will have it repaired, and have it serviced at the recommended intervals in the future so it doesn't break unexpectedly again.

This technique was originally developed by Sakichi Toyoda and was later used by Toyota during the evolution of their manufacturing methodologies. Taiichi Ohno, the architect of the Toyota Production System, described the Five whys method as "the basis of Toyota's scientific approach . . . by repeating why five times, the nature of the problem as well as its solution becomes clear."

The tool has seen widespread use beyond Toyota, and is now used within Kaizen, lean manufacturing, and Six Sigma.

"If you don't ask the right questions, you don't get the right answers. A question asked in the right way often points to its own answer. Asking questions is the ABC of diagnosis. Only the inquiring mind solves problems." -- Edward Hodnett