|July 11, 2001||Volume 1, Issue 28|
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by Rick Brenner
Although we sometimes make decisions with incomplete information, we do the best we can, given what we know. Sometimes, we make wrong decisions not because we have incomplete information, but because we make mistakes in how we reason about the information we do have.
Ginny was getting pretty steamed. "We tried code inspections back in Release 5, and you know what happened then. Everything slowed down, we got nothing done, everyone got into fights, and Morgan left the group. If we have to do inspections, you can count me out." Ginny's argument, in essence, was that since some unpleasant events happened shortly after inspections began, the code inspections caused them.
Arguments based on
the Fallacy of the False Cause
to make costly errorsAlthough her argument is convincing to many, it doesn't prove her case. It's an example of a rhetorical fallacy called post hoc ergo propter hoc — Latin for after this, therefore because of this. Ginny argues that since the unpleasant events followed the adoption of code inspections, the code inspections caused the problems, and therefore all code inspections, of any kind whatever, are bad.
A more convincing argument would exclude other possible causes. For example, were the inspections run badly? Were people inadequately trained? Were inspections introduced when people were too busy to learn how to do inspections?
The Post Hoc fallacy is a special case of a more general type of fallacy — the fallacy of the false cause. In Post Hoc, the apparent causal connection relates to the timing of the two events. But connections can also be unrelated to timing:
All of the projects Gerhard has managed in the past few years have been late and over budget. Since people now believe that Gerhard was the cause of the overruns, he can no longer get assignments as a project lead. Nobody seems to remember that each of Gerhard's project sponsors had either reduced his budget or expanded requirements so many times that no project manager would have had much of a chance to perform well.
Gerhard's management skill was the most obvious factor common to the failed projects, but it wasn't the cause. In this case, faulty reasoning damages a career and deprives the company of a skilled manager.
How can you spot this kind of error in the heat of debate? The fallacy of the false cause might be lurking if the argument states that:
Since A was present when B occurred, then A was the cause. Or Since A preceded B, A caused B.
To respond to arguments that use this fallacy, use examples in which A was present, but B wasn't. Your debate partner might not be convinced, but it's your best shot.
Educate your colleagues about the Fallacy of the False Cause. When we understand how much it can cost, and when we understand how to avoid it, we can save much pain and frustration. Perhaps Will Rogers said it best:
It's not what we don't know that hurts; it's what we know that ain't so.
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