The 5 Why’s is the practice of asking the question ‘why’ five or more times to discover the route cause that may not be obvious to begin with.
Toyoda Sakichi, the Japanese inventor, and industrialist, most famously known as the founder of ‘Toyota Industries,’ and for his invention of the first automatic shuttle-changing mechanism, was the original creator of the ‘5 Why’s’ method.
This method gained a greater reputation through the Japanese industrial engineer Ōno Taiichi. He was the father of the Toyota Production System which inspired Lean Manufacturing in the US. Taiichi believed that “by repeating why five times, the nature of the problem as well as its solution becomes clear.”
Most used within manufacturing or engineering, the ‘5 Why’s’ method can be used to solve both simple and difficult problems.
Identify the Problem: We must first identify the problem to tackle. For this example, we shall use the issue, “Vehicle will not start.”
Ask "Why?": Ask why the problem happened and begin to identify the issue by narrowing down outcomes.
Analyse the Answer: Use the answers to ask another "Why?"
Repeat: Continue asking "Why?" for a total of five times, or until you reach the root cause of the problem.
It must be noted that this method may not be useful for complex problems, with the former managing director global purchasing for Toyota commenting that the tool suffers from being “too basic” to analyse root causes to assure that issues are fixed.
The University of Derby is partnered with ‘Toyota City’, Japan. This partnership stems from the establishment of the Toyota Motor Companies first European car factory in Burnaston, South Derbyshire in 1989. As a result, Derbyshire City Council and Toyota City formalised a twinning agreement in 1998.
‘Toyota City’; located in the Aichi Prefecture of Honshu, was originally known as Kokomo City, but was renamed in 1959 in recognition of the economic significance of Toyota Motor Corporation, founded by Kiichiro Toyoda, the son of Sakichi Toyoda.
Derbyshire County Council (2024). Toyota City, Japan - Derbyshire County Council. [online] Derbyshire.gov.uk. Available at: https://www.derbyshire.gov.uk/community/twinning/toyota-city/toyota-city-japan.aspx.
Ohno, T. (1988). Toyota Production System : beyond large-scale Production.
[You may note that in other texts, these names may be reversed. Traditionally, in 19th century Japan, family names (surnames) come before the given name. Towards the latter of the 19th century this became outdated and began to favour the western choice of placing the family name last; especially within educational settings.]
