§5 Causal Fallacies and Confusions

Because causal reasoning is inductive and probabilistic, it is the most common site for logical errors. The human brain is evolutionarily primed to find patterns, which often leads us to see a “cause” where there is only a coincidence. To be a Reasonable Person, one must distinguish between a genuine causal mechanism and a mere temporal or statistical association.

5.1 Post Hoc, Ergo Propter Hoc (False Cause)

The name is Latin for “After this, therefore because of this.” This fallacy occurs when we assume that because Event B happened after Event A, Event A must have caused Event B.

• The Philosophical Error: As David Hume noted, “priority in time” is a necessary part of our perception of causation, but it is not sufficient to prove causation.

• Example: “I wore my lucky socks, and then I won the game. Therefore, the socks caused the win.”

• Critical Defense: Ask if there is a physical or logical Efficient Cause (the “mechanism”) connecting the two events, or if it is merely a sequence.

5.2 Mistaking Correlation for Causation

This is perhaps the most frequent error in media and social science reporting. A correlation is a statistical relationship where two variables move together, but one does not necessarily drive the other.

• The Third Factor (Common Cause): Often, $X$ and $Y$ are correlated not because $X$ causes $Y$, but because a third factor, $Z$, causes both.

  • Example: Ice cream sales and drowning rates are highly correlated. Does ice cream cause drowning? No. The third factor ($Z$) is Hot Weather, which causes people to both buy ice cream and go swimming.

• Coincidence: Sometimes, two variables correlate purely by chance. Philosophers call these “spurious correlations.”

5.3 Confusing Cause and Effect (Reversibility)

Sometimes a causal link exists, but we get the direction of the “arrow” backward.

• Example: A study finds that people who exercise more have lower levels of depression. Does exercise cause happiness, or are happy people simply more motivated to exercise?

• Critical Defense: Use Mill’s Method of Difference—if we intervene and force exercise on a sedentary group, does their depression drop? If so, the direction is confirmed.

5.4 The Fallacy of the Single Cause

This occurs when we assume there is one “silver bullet” cause for a complex event, ignoring the INUS conditions (Section 1.4).

• Example: “The high school dropout rate is caused by bad teachers.” This ignores the web of material causes (funding), formal causes (curriculum), and social causes (poverty) that contribute to the effect.

5.5 Being Misled by Coincidence

As the philosopher Hans Reichenbach explored in The Direction of Time, humans often underestimate the “Law of Large Numbers.” In a world of 8 billion people, improbable coincidences (like dreaming of a friend right before they call) are statistically certain to happen to someone every single day. We tend to remember the “hits” and forget the millions of “misses,” a form of Confirmation Bias.

§5 Summary Table: Causal Pitfalls