Post Hoc Fallacy: Does “After This” Really Mean “Because of This”?
The post hoc fallacy assumes that because one event came after another, the first caused the second. This guide explains the Latin phrase, shows examples from health, politics and superstition, lists the tests that separate cause from coincidence, and gives a reply for debates.
Updated 2026-11-04
What is the post hoc fallacy?
Post hoc ergo propter hoc is Latin for “after this, therefore because of this.” The fallacy is to infer that A caused B simply because A happened before B. Time order is a requirement for causation, since a cause cannot come after its effect, but it is not proof.
The classic illustration is the rooster. A rooster crows before sunrise every morning, but the crowing does not cause the sun to rise. Another is a superstition: a player wears lucky socks and the team wins. Many cases are subtler, such as a government introducing a policy and a statistic improving the next year, when other factors may have been at work.
The pattern to look for
The argument typically has this shape.
- Event A occurs.
- Event B occurs afterwards.
- Therefore, A caused B.
- No other explanation is considered, and no mechanism or comparison is offered.
Examples in everyday talk and debate
The same error appears in different settings. These examples show the pattern and what is missing from each.
| Claim | Sequence | Other explanations |
|---|---|---|
| “I took a herbal remedy and my cold cleared up.” | Remedy, then recovery | Most colds clear up on their own in a week or so. |
| “Crime fell after the new mayor took office.” | Election, then lower crime | Long-term trends, economic shifts, policing changes that began earlier. |
| “The team won after we changed the coach.” | Coaching change, then win | Easier fixtures, returning players, luck. |
| “Grades dropped after the school introduced tablets.” | Tablets, then lower grades | A new curriculum, a change in intake, test difficulty. |
| “The market rose after the announcement.” | Announcement, then rise | Earnings reports, global events, unrelated news. |
| “Our new website design led to more sales.” | Redesign, then sales rise | A seasonal peak, a marketing campaign, price changes. |
Why it is persuasive
The mind looks for patterns and stories. When one event follows another, we naturally connect them. Time order feels like a thread, and the story it tells is simple. People also tend to act when things are at their worst, so a treatment or policy often follows a low point and the subsequent improvement is credited to it. This is called regression to the mean: extremes tend to be followed by more average results regardless of what was done.
It is also persuasive because it often feels like common sense. If you changed something and the result changed, the connection seems obvious. That is why this fallacy is common in health claims, politics and business.
Watch it explained
A short video can make the pattern easier to spot the next time you hear it.
Watch: Critical Thinking: Fallacies: Post Hoc Ergo Propter Hoc (Wireless Philosophy). Why coming after is not the same as being caused by.
Watch: Critical Thinking: Fundamentals: Correlation and Causation (Wireless Philosophy). Why two things moving together need not be linked.
When it is not a fallacy
Sequence can be part of good causal reasoning. In a well-designed experiment, a treatment is applied and the outcome is measured afterwards, and the treatment group is compared with a control group. In that case, the order matters, but it is combined with other evidence. A strong causal claim also has a plausible mechanism and holds up when other factors are accounted for.
A single clear case can also be convincing when the link is direct and there is no plausible alternative: you flip a switch and the light comes on, every time. The fallacy arises when sequence is the only evidence for a claim that has many possible causes.
How to respond
Do not simply say “correlation is not causation”; show what is missing.
- Grant the order of events, then ask whether it shows cause.
- Offer at least one other explanation and ask why it is ruled out.
- Ask what would have happened without the first event: is there a comparison group?
- Ask for the mechanism: how, exactly, did A produce B?
- Ask whether the pattern repeats in other cases, and whether the size of the effect fits the cause.
Using this in a debate
Post hoc reasoning is rife in policy debates, where each side credits or blames a policy for subsequent changes. A strong speaker will ask for the counterfactual: what do we expect would have happened anyway? Evidence from comparison, such as other regions that did not adopt the policy, or from trends before the change, is more persuasive than a before-and-after claim.
When you make a causal claim yourself, include the checks: give the timeline, offer a mechanism, point to a comparison, and say what other factors you considered. It makes the claim harder to dismiss and shows judges you have thought about it.
Four checks before you say “because”
Four questions separate a causal claim from a coincidence. First, timing: did the cause come before the effect, and is the gap plausible? Second, mechanism: can you explain how one led to the other? Third, comparison: what happened where the cause was absent? Fourth, alternatives: what else changed at the same time, and why is it not the explanation? If a claim cannot answer the third and fourth questions, treat it as a hypothesis to test, not a finding. In a debate, saying so openly is a strength: “This is consistent with our argument, and here is what would count against it.”
Related fallacies
These are easy to confuse with this one, or often appear alongside it.
- False cause (non causa pro causa): the broader family of causal mistakes.
- Correlation versus causation: two things move together without one causing the other.
- Regression to the mean: extremes followed by more typical results.
- Single cause fallacy: assuming only one cause when there are many.
Frequently asked questions
What does post hoc ergo propter hoc mean?
It is Latin for “after this, therefore because of this.” It names the fallacy of assuming that an event that follows another was caused by it.
What is an example of the post hoc fallacy?
“I started taking vitamin C and my cold went away, so vitamin C cured it.” Most colds go away on their own, so the timing proves nothing.
What is the difference between post hoc and correlation?
Post hoc is based on one event following another. Correlation is a statistical relationship between two variables. Both can mislead if used as proof of cause.
How can I show cause and not just sequence?
Show a mechanism, compare with cases where the supposed cause was absent, rule out other explanations, and, where possible, use a controlled experiment.
Is post hoc the same as false cause?
Post hoc is a type of false cause. False cause also covers errors such as confusing correlation with causation and reversing cause and effect.
Sources and further reading
- Post hoc ergo propter hoc (Wikipedia)
- Correlation does not imply causation (Wikipedia)
- Logical Fallacies (Purdue Online Writing Lab)
- Fallacies (UNC Writing Center)
- Fallacies (Internet Encyclopedia of Philosophy)