This fallacy has the following general form:
The general idea behind this fallacy is that it is an error in reasoning to conclude that one thing causes another simply because the two are associated on a regular basis. More formally, this fallacy is committed when it is concluded that A is the cause of B simply because they are associated on a regular basis. The error being made is that a causal conclusion is being drawn from inadequate evidence.
The Questionable Cause Fallacy is actually a general type of fallacy. Any causal fallacy that involves an error in a reasoning due to a failure to adequately investigate the suspected cause is a fallacy of this type. Thus, fallacies like Post Hoc and Confusing Cause and Effect are specific examples of the general Questionable Cause Fallacy.
Causal reasoning can be quite difficult since causation is a rather complex philosophic issue. The complexity of causation is briefly discussed in the context of the specific versions of this fallacy.
The key to avoiding the Questionable Cause fallacy is to take due care in drawing causal conclusions. This requires taking steps to adequately investigate the phenomena in question as well using the proper methods of careful investigation.
Description of Ignoring a Common Cause
One day Bill wakes up with a fever. A few hours later he finds red spots on his skin. he concludes that the fever must have caused the red spots. His friend insists that the spots and the fever are caused by some microbe. Bill laughs at this and insists that if he spends the day in a tub of cold water his spots will go away.
Over the course of several weeks the needles from the pine trees along the Wombat river fell into the water. Shortly thereafter, many dead fish washed up on the river banks. When the EPA investigated, the owners of the Wombat River Chemical Company claimed that is it was obvious that the pine needles had killed the fish. Many local environmentalists claimed that the chemical plant's toxic wastes caused both the trees and the fish to die and that the pine needles had no real effect on the fish.
A thunderstorm wakes Joe up in the middle of the night. He goes downstairs to
get some milk to help him get back to sleep. On the way to the refrigerator, he
notices that the barometer has fallen a great deal. Joe concludes that the storm
caused the barometer to fall. In the morning he tells his wife about his
conclusion. She tells him that it was a drop in atmospheric pressure that caused
the barometer to drop and the storm.
Joe gets a chain letter that threatens him with dire consequences if he breaks the chain. He laughs at it and throws it in the garbage. On his way to work he slips and breaks his leg. When he gets back from the hospital he sends out 200 copies of the chain letter, hoping to avoid further accidents.When investigating a small pond a group of graduate students found that there was a severe drop in the fish population. Further investigation revealed that the fishes' food supply had also been severely reduced. At first the students believed that the lack of food was killing the fish, but then they realized they had to find what was causing the decline in the food supply. The students suspected acid rain was the cause of both the reduction in the fish population as well as the food supply. However, the local business council insisted that it was just the lack of food that caused the reduction in the fish population. Most of the townspeople agreed with this conclusion since it seemed pretty obvious that a lack of food would cause fish to die.