Causal Fallacies
Misidentifying Relevant Factors
A key issue in any type of causal reasoning is whether the factors preceding an effect are truly relevant to that effect. In the Method of Agreement, for example, it's easy to find a preceding factor common to all occurrences of a phenomenon. But that factor may be irrelevant. Relevant factors include only those things that could possibly be causally connected to the occurrence of the phenomenon being studied. Lack of background knowledge might lead you to dismiss or ignore relevant factors or to assume that irrelevant factors must play a role.
Post Hoc
A particularly prevalent type of misjudgment about coincidences is the logical fallacy known as post hoc, ergo propter hoc ("after that, therefore because of that").
Correlation
A very important cautionary note must accompany this discussion of correlation. Correlation, of course, does not always mean that a causal relationship is present. A correlation could just be a coincidence.
Correlation
An increase in home PC sales is correlated with a rise in the incidence of AIDS in Africa, but this doesn't mean that one is in any way causally linked with the other.
Confusing Cause and Effect
As you can see, it's not always a simple matter to discern what the nature of a causal link is. We must rely on this rule of thumb: Don't assume that a causal connection exists unless you have good reason for doing so.
Confusing Cause and Effect
Does participation in high school sports produce desirable virtues such as courage and self-reliance—or do the virtues of courage and self-reliance lead students to participate in high school sports?
Confusing Cause and Effect
Does your coffee drinking cause you to feel stressed out—or do your feelings of being stressed out cause you to drink coffee?
Post Hoc
Jasmine left her umbrella at home Monday, and this caused it to rain I wore my blank shirt on Tuesday and got an F on a math quiz. I wore the same shirt the next day and flunked my psych exam. That skirt's bad luck
Misidentifying Relevant Factors
Let's say that all those who got sick in Elmo's bar had black hair. So what? We know that hair color is very unlikely to be related to intestinal illness.
Being Misled by Coincidence
Plenty of interesting pairings can also show up in scientific research. Scientists might friend, for example, that men with the highest rates of heart disease may also have a higher daily intake of water. Or women with the lowest risk of breast cancer may own Toyotas. Such pairings are very probably just coincidence, merely interesting correlations of events. A problem arises, though, when we think that there must be a causal connection involved.
Being Misled by Coincidence
Sometimes ordinary events are paired in unusual or interesting ways: You think of Hawaii, then suddenly a TV ad announces low-cost fares to Maui; you receive some email just as your doorbell sounds and the phone rings; or you stand in the lobby of a hotel thinking of an old friend—then see her walk by.
Confusing Cause and Effect
Sometimes we may realize that there's a causal relationship between two factors—but we may not know which factor is the cause and which is the effect. We may be confused, for example, about the answers to questions like these: