A previous article discussed the definition of the word root as it applies to the concept of Root Cause. However, that article did not provide a definition for the word cause. While the meaning of cause may seem obvious to the casual observer, this article will develop a very precise definition that is useful for any incident investigator performing a root cause analysis.
One simple, general definition of cause is the producer of an effect. This isn't a very precise definition, but we can use it to get at something more useful. Let us break it down into components with that goal in mind.
First, consider the concept of an effect. The word itself is fairly ambiguous, because it is so often tied to the word cause, as in cause and effect. Looking at the concept intuitively, however, yields some insight. What is the difference between having an effect, versus having no effect?
In a situation where some action was taken, but there is no effect, then nothing changed. If there was an effect, then something must have changed. The difference is then the presence or lack of a change. In essence, an effect is a change.
Our definition for cause can now be written as the producer of a change. Let us now try to refine this by expanding upon the concept of a producer. What is required to produce a change?
A change requires that there be a discrete difference between initial and final states. Except for processes like radioactive decay, where the impetus driving the change of state is completely internal, there must be an external driver. Additionally, there are usually other factors required to exist coincident with the driver.
What is required, then, is a set of factors sufficient to drive a particular change of state. One or more of these factors may be active in nature, such as an action or another change. Others may be passive or constant, such as local ambient conditions or object properties.
Given a set of factors sufficient to drive a change, it would be instructive to ask what happens if one or more of the factors were not present. If the factor is not necessary, then it doesn't matter whether it does or does not exist. However, if the factor truly is necessary but not present, then the change cannot happen.
So, in order for a change to be produced, we must have a sufficient set of factors in which all necessary factors are present. If any of the necessary factors are not present, the change does not occur -- each of the necessary factors is a sort of on/off switch for the given change. In this sense, each of the necessary Causal Factors can be considered a cause of the effect.
Incorporating all the points discussed above leads to the following definition for cause:
A cause is any necessary component of a set of factors sufficient to drive a change.
This definition is somewhat wordy, but is very precise. It is also valuable because it provides a clear test of whether an action or condition is in fact a cause for a given effect: the Necessary and Sufficient test. Using this definition, it is possible to screen out factors that are irrelevant. Conversely, this definition can be used to identify missing evidence or even rule out invalid hypotheses.
by Bill Wilson