January 7, 2026 | Mark Paradies

Does an Incident Have a Single Root Cause?

comparing root cause analysis techniques

Before You Can Answer the Question Above, You Have to Define a Root Cause

There are many definitions of the term “root cause.” For example, DOE Guideline DOE-NE-STD-1004-92 defines a root cause as:

The cause that, if corrected, would prevent recurrence of this and similar occurrences. The root cause does not apply to this occurrence only, but has generic implications to a broad group of possible occurrences, and it is the most fundamental aspect of the cause that can logically be identified and corrected. There may be a series of causes that can be identified, one leading to another. This series should be pursued until the fundamental, correctable cause has been identified.

This seems to imply that each incident has only one root cause.

The online Collins Dictionary defines a root cause as:

The fundamental reason for the occurance of a problem.

This definition also implies a single root cause.

I was part of an IEEE standards committee that disagreed with the definition of a root cause as being singular. In 2014, we eventually agreed on this definition:

The basic reason(s) for a problem, that, if corrected,
will prevent recurrence of the problem.

Note that this definition suggests that there is a basic reason or reasons. Thus, there can be multiple root causes for an incident.

In the TapRooT® Root Cause Analysis System, the early definition that we used in the 1990s was:

A root cause is
the most basic cause (or causes)
that can reasonably be identified
that management has control to fix
and, when fixed, will prevent
(or significantly reduce the likelihood of)
the problem’s recurrence.

From the start, we understood that there could be multiple root causes.

In 2006, we updated the TapRooT® System definition of a root cause to:

A Root Cause is
the absence of a best practice
or the failure to apply knowledge
that would have prevented the problem.

In every case, there have always been multiple best practices and failures to apply knowledge for a single incident. Thus, we believe there are always multiple root causes for any significant incident.

What Difference Does It Make?

So what difference does it make if you say there can be only one root cause or you think there are multiple root causes?

First, I have seen investigators, investigation teams, and management waste valuable time arguing over what is the “rootiest” root cause. I claim that the time was wasted because often there were multiple corrective actions (best practices or knowledge) that needed to be applied to prevent similar incidents. And deciding which was the rootiest root cause did little if anything to improve the corrective actions that were going to be applied. It is seldom productive to argue over which is the rootiest root cause or the highest priority corrective action.

Second, focusing on a single root cause can often lead to missing other, equally important root causes. Missing these root causes means that effective corrective actions aren’t developed for these causes and, therefore, their associated problems are left unsolved. These unsolved problems can lead to future incidents that are slightly different. Incidents that, under different circumstances, may be more severe.

Finally, blame-oriented root cause systems often find human error as the single root cause. This focus on who is to blame is ineffective in preventing future incidents. It often leads to mysterious incidents because the people involved are less than forthcoming with information to the investigative team. As Bart Simpson said: