Post hoc ergo propter hoc

This article is about the informal fallacy. For the West Wing episode, see Post Hoc, Ergo Propter Hoc (The West Wing). For other uses, see Post hoc.

Post hoc ergo propter hoc (Latin: 'after this, therefore because of this') is an informal fallacy. Its a fallacy in which an event is presumed to have been caused by a closely preceding event merely on the grounds of temporal succession. This type of reasoning is fallacious because mere temporal succession does not establish a causal connection.^[1][2] It is often shortened simply to post hoc fallacy. This kind of reasoning is quite common and lies behind most forms of superstition. (Example: “A black cat crossed my path and later I tripped and sprained my ankle. It must be that black cats really are bad luck.”)^[2]

Post hoc is a particularly tempting error because correlation sometimes appears to suggest causality. The fallacy lies in a conclusion based solely on the order of events, rather than taking into account other factors potentially responsible for the result that might rule out the connection.^[3] Post hoc ergo propter hoc is an easy fallacy to detect when it is blatant, but even the best of scientists and statesmen are occasionally misled by it.^[1]

Pattern

The form of the post hoc fallacy is expressed as follows:

• A occurred, then B occurred.
• Therefore, A caused B.

When B is undesirable, this pattern is often combined with the formal fallacy of denying the antecedent, assuming the logical inverse holds: believing that avoiding A will prevent B.^[4]

Examples

• A tenant moves into an apartment and the building's furnace develops a fault. The manager blames the tenant's arrival for the malfunction. One event merely followed the other, in the absence of causality.^[5]
• During the past two months, every time that the cheerleaders have worn blue ribbons in their hair, the basketball team has been defeated. Therefore, to prevent defeats in the future, the cheerleaders should get rid of those blue ribbons.^[2]
• Reporting of coincidental vaccine adverse events, where people have a health complaint after being vaccinated and assume it was caused by the vaccination.^[6]

See also

• Apophenia – Tendency to perceive connections between unrelated things
• Affirming the consequent – Type of fallacious argument (logical fallacy)
• Association fallacy – Informal inductive fallacy
• Cargo cult – New religious movement
• Causal inference – Branch of statistics concerned with inferring causal relationships between variables
• Coincidence – Concurrence of events with no connection
• Confirmation bias – Bias confirming existing attitudes
• Correlation does not imply causation – Refutation of a logical fallacy
• Jumping to conclusions – Psychological term
• Magical thinking – Belief in the connection of unrelated events
• Superstition – Belief or behavior that is considered irrational or supernatural
• Survivorship bias – Logical error, form of selection bias
• Surrogate endpoint
• Texas sharpshooter fallacy

Bibliography

1. Woods, J. H., Walton, D. N. (1977). Post Hoc, Ergo Propter Hoc.
2. Mommsen, J. K. F. (2013). Wider Das Post Hoc Ergo Propter Hoc - Primary Source Edition. United States: BiblioLife.
3. Woods, J., Walton, D. (2019). Fallacies: Selected Papers 1972–1982. Germany: De Gruyter.

References

1. Cope, Irving M; Cohen, Carl; McMahon, Kenneth (2016). Introduction to logic (in 639-2) (14th ed.). Routledge. p. 172. ISBN 9780205820375.{{cite book}}: CS1 maint: unrecognized language (link)
2. Hurley, Patrick J. A Concise Introduction to Logic (11th ed.). p. 143. ISBN 9780495504047.
3. "post hoc". LII / Legal Information Institute. Retrieved 2021-08-28.
4. Summers, Jesse S. (24 March 2017). "Post hoc ergo propter hoc : some benefits of rationalization". Philosophical Explorations. 20 (sup1): 21–36. doi:10.1080/13869795.2017.1287292. S2CID 151401300.
5. Damer, T Edward (1995). Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments (3rd ed.). Belmont, CA: Wadsworth Publishing. p. 131. ISBN 978-0-534-21750-1. OCLC 30319422.
6. Manktelow, K. I. (2012). Thinking and Reasoning: An Introduction to the Psychology of Reason, Judgment and Decision Making. Psychology Press. p. 119. ISBN 9781841697413.