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'''5 Whys''' is an iterative interrogative [[Philosophy:Skill|technique]] used to explore the [[Causality|cause-and-effect]] relationships underlying a particular problem.<ref>{{cite web|title=Five Whys Technique|url=http://www.adb.org/publications/five-whys-technique|work=adb.org|publisher=Asian Development Bank|accessdate=26 March 2012  |date=February 2009}}</ref> The primary goal of the technique is to determine the root cause of a defect or problem by repeating the question "Why?" Each answer forms the basis of the next question. The "5" in the name derives from an anecdotal observation on the number of iterations needed to resolve the problem.
Not all problems have a single root cause. If one wishes to uncover multiple root causes, the method must be repeated asking a different sequence of questions each time.

The method provides no hard and fast rules about what lines of questions to explore, or how long to continue the search for additional root causes. Thus, even when the method is closely followed, the outcome still depends upon the knowledge and persistence of the people involved.

== Example == 

*The vehicle will not start. (the problem)
#'''''Why?''''' - The battery is dead. (First why)
#'''''Why?''''' - The alternator is not functioning. (Second why)
#'''''Why?'' '''- The alternator belt has broken. (Third why)
#'''''Why?''''' - The alternator belt was well beyond its useful service life and not replaced. (Fourth why)
#'''''Why?''''' - The vehicle was not maintained according to the recommended service schedule. (Fifth why, a root cause)<ref>{{cite book|last1=Spears|first1=Stephen|title=The High Velocity Edge}}</ref>

The questioning for this example could be taken further to a sixth, seventh, or higher level, but five [[Iteration|iteration]]s of asking why is generally sufficient to get to a root cause.{{Citation needed|date=January 2018}}  The key is to encourage the trouble-shooter to avoid assumptions and logic traps and instead trace the chain of causality in direct increments from the effect through any layers of abstraction to a root cause that still has some connection to the original problem. Note that, in this example, the fifth why suggests a broken process or an alterable behaviour, which is indicative of reaching the root-cause level.

The last answer points to a process. This is one of the most important aspects in the 5 Why approach - the ''real'' root cause should point toward a process that is not working well or does not exist.<ref>Ivan Fantin (2014). Applied Problem Solving. Method, Applications, Root Causes, Countermeasures, Poka-Yoke and A3. How to make things happen to solve problems. Milan, Italy: Createspace, an Amazon company. {{ISBN|978-1499122282}}</ref> Untrained facilitators will often observe that answers seem to point towards classical answers such as not enough time, not enough investments, or not enough manpower. These answers may be true, but they are out of our control. Therefore, instead of asking the question ''why?'', ask ''why did the process fail?''

A key phrase to keep in mind in any 5 Why exercise is "people do not fail, processes do". [citation needed?]

== History ==
The technique was originally developed by Sakichi Toyoda and was used within the [[Company:Toyota|Toyota]] Motor Corporation during the evolution of its manufacturing methodologies.  It is a critical component of problem-solving training, delivered as part of the induction into the [[Finance:Toyota Production System|Toyota Production System]]. The architect of the Toyota Production System, Taiichi Ohno, described the 5 Whys method as "the basis of Toyota's scientific approach by repeating why five times<ref>{{cite web |url=https://www.toyota-global.com/company/toyota_traditions/quality/mar_apr_2006.html |title=Ask 'why' five times about every matter |accessdate=2006-03-06 }}</ref> the nature of the problem as well as its solution becomes clear."<ref>{{cite book |author=Taiichi Ohno; foreword by Norman Bodek |title=Toyota production system: beyond large-scale production |publisher=Productivity Press |location=Portland, Or |year=1988 |isbn=0-915299-14-3 }}</ref> The tool has seen widespread use beyond Toyota, and is now used within [[Finance:Kaizen|Kaizen]], [[Finance:Lean manufacturing|lean manufacturing]], and [[Six Sigma]].
In other companies, it appears in other forms.  Under Ricardo Semler, Semco practices "three whys" and broadens the practice to cover goal setting and decision making.<ref>{{cite book |last=Semler |first=Ricardo | date=2004 |title=The Seven-Day Weekend |publisher=Penguin |quote="Ask why.  Ask it all the time, ask it any day, and always ask it three times in a row." |isbn=9781101216200}}</ref>

== Techniques ==
Two primary techniques are used to perform a 5 Whys analysis:<ref>{{cite web |url=http://blog.bulsuk.com/2009/03/5-why-finding-root-causes.html |title=An Introduction to 5-why |accessdate=2010-03-06 }}</ref>
*the [[Ishikawa diagram|fishbone (or Ishikawa) diagram]]
*a tabular format
These tools allow for analysis to be branched in order to provide multiple root causes.<ref>{{cite web |url=http://blog.bulsuk.com/2009/07/5-why-analysis-using-table.html |title=5-why Analysis using an Excel Spreadsheet Table |accessdate=2010-12-25 }}</ref>

== Rules of performing 5 Whys ==
In order to carry out the 5-Why analysis properly, the following advice should be followed:{{Citation needed|reason=why should these advices be followed?|date=July 2016}}
# It is necessary to engage the management in the 5Whys process in the company. For the analysis itself, consider what is the right working group. Also consider bringing in a facilitator for more difficult topics.
# Use paper or whiteboard instead of computers.
# Write down the problem and make sure that all people understand it.
# Distinguish causes from symptoms.
# Pay attention to the logic of cause-and-effect relationship.
# Make sure that root causes certainly lead to the mistake by reversing the sentences created as a result of the analysis with the use of the expression "and therefore". 
# Try to make our answers more precise.
# Look for the cause step by step. Don't jump to conclusions.
# Base our statements on facts and knowledge.
# Assess the process, not people.
# Never leave "human error", "worker's inattention", "blame John" etc., as the root cause.
# Foster an atmosphere of trust and sincerity.
# Ask the question "Why" until the root cause is determined, i.e. the cause the elimination of which will prevent the error from occurring again.<ref>{{Cite book|title = 5xWhys. Method First Handbook.|last = Brożyńska|first = Martyna|last2 = Kowal|first2 = Krzysztof|last3 = Lis|first3 = Anna|last4 = Szymczak|first4 = Michał|publisher = 2K Consulting|year = 2016|isbn = 978-83-939309-2-0|location = Łódź, Poland|pages = 34}}</ref>
# When you form the answer for question "Why" - it should happen from the customer's point of view.

== Criticism ==

While the 5 Whys is a powerful tool for engineers or technically savvy individuals to help get to the true causes of problems, it has been criticized by Teruyuki Minoura, former managing director of global purchasing for Toyota, as being too basic a tool to analyze root causes to the depth that is needed to ensure that they are fixed.<ref>{{cite web|url=http://www.toyotageorgetown.com/tpsoverview.asp|title=The "Thinking" Production System: TPS as a winning strategy for developing people in the global manufacturing environment|accessdate=2014-02-19|archive-url=https://web.archive.org/web/20140227050644/http://www.toyotageorgetown.com/tpsoverview.asp|archive-date=2014-02-27|dead-url=yes|df=}}</ref> Reasons for this criticism include:

*Tendency for investigators to stop at symptoms rather than going on to lower-level root causes.
*Inability to go beyond the investigator's current knowledge - cannot find causes that they do not already know.
*Lack of support to help the investigator ask the right "why" questions.
*Results are not repeatable - different people using 5 Whys come up with different causes for the same problem.
*Tendency to isolate a single root cause, whereas each question could elicit many different root causes.

These can be significant problems when the method is applied through deduction only. On-the-spot verification of the answer to the current "why" question before proceeding to the next is recommended to avoid these issues. In addition, performing logical tests for [[Necessity and sufficiency|necessity and sufficiency]] at each level can help avoid the selection of spurious causes and promote the consideration of multiple root causes.<ref>{{cite web|last1=Wilson|first1=Bill|title=Five-by-Five Whys|url=http://www.bill-wilson.net/b73|website=www.bill-wilson.net|accessdate=7 October 2014}}</ref>

==See also==
<!-- New links in alphabetical order please -->
* [[Causality]]
* Eight Disciplines Problem Solving
* [[Five Ws]] (information-gathering)
* [[Philosophy:Four causes|Four causes]]
* Issue map
* [[Issue tree]]
* [[Root cause analysis]]
* [[Philosophy:Socratic method|Socratic method]]
* [[Why–because analysis]]

==References==
{{reflist}}
[[Category:Problem solving methods]]
[[Category:Lean manufacturing]]

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