Post Hoc Fallacy: Definition & Examples
The post hoc fallacy — short for post hoc ergo propter hoc (Latin for "after this, therefore because of this") — is a logical error that assumes because one event followed another, the first event caused the second. It's one of the most common reasoning mistakes in everyday life, politics, and media.
The Pattern
A happened, then B happened. Therefore, A caused B.
The flaw: sequence alone doesn't prove causation. There may be a third factor, or the connection may be pure coincidence.
Correlation vs. Causation
Two things can be correlated — they happen together or in sequence — without one causing the other. Ice cream sales and drowning rates both rise in summer, but ice cream doesn't cause drowning. The shared cause is hot weather. The post hoc fallacy ignores these alternative explanations and jumps straight to a causal claim based on timing alone.
15+ Post Hoc Fallacy Examples
Everyday Superstitions
- —I wore my lucky socks and we won the game — the socks must be lucky.
- —I broke a mirror and then had a bad week. Breaking the mirror caused the bad luck.
- —Every time I wash my car, it rains the next day.
- —I forgot to knock on wood and then failed the test.
- —A black cat crossed my path and I tripped — the cat caused it.
Health & Wellness
- —I started taking a supplement and my cold went away two days later — the supplement cured me.
- —She ate organic food and never got sick, so organic food prevents illness.
- —He stopped eating gluten and felt happier, so gluten must cause depression.
- —I did a "detox cleanse" and felt better afterward — the toxins must have been removed.
Politics & Media
- —Crime rates dropped after the new mayor took office, so the mayor reduced crime.
- —The economy improved after the policy was signed — the policy fixed the economy.
- —Violent video games became popular and youth aggression increased — games cause violence.
- —Social media grew and teen anxiety rose, so social media must be the sole cause.
Technology & Business
- —We redesigned our website and sales went up — the redesign boosted sales. (Ignoring a seasonal spike.)
- —The company hired a new CEO and profits rose the next quarter — the CEO turned things around.
- —We ran an ad campaign and got more traffic, so the ads worked. (Ignoring a viral social media mention.)
Personal Relationships
- —I texted her and she didn't reply, then it rained — my text ruined the weather. (Absurd, but illustrates the structure.)
- —After he moved to a new city, his friendships faded — moving must destroy friendships.
- —She started meditating and her marriage improved — meditation fixed the relationship.
How to Avoid the Post Hoc Fallacy
Ask: is there a third factor?
Before assuming A caused B, consider whether a hidden variable (C) could explain both events. The classic example: rooster crows, then the sun rises — but the rooster doesn't cause sunrise. Earth's rotation causes both.
Look for controlled evidence
Genuine causation is established through controlled experiments, not anecdotes. When someone claims a supplement "works" because they felt better after taking it, a proper study would compare outcomes with and without the supplement while controlling for other variables.
Consider coincidence
Sometimes things just happen in sequence. The human brain is wired to find patterns, even where none exist. Recognizing this tendency is the first step toward more rigorous thinking — and more persuasive writing.
Using post hoc in your writing
As a writer, you can use the post hoc fallacy intentionally — to reveal a character's superstitious thinking, create dramatic irony, or build unreliable narration. Knowing the fallacy lets you deploy it as a storytelling tool rather than falling into it accidentally in your arguments or essays.
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