Also known as: post hoc ergo propter hoc · post hoc · propter hoc · post hoc fallacy
Written by attorneys · grounded in primary & secondary sources — see below
A logical fallacy that infers a causal connection between two events merely because one follows the other in time. The error arises when sequence is treated as proof of causation without evidence that the first event produced the second. Courts reject the inference when the record shows only temporal order and no further link between the conduct and the harm.
Pierce Patterson sued a university in federal court. The judge had once served as a trustee during negotiations with the university but learned of the connection only after judgment. Pierce moved to vacate, arguing that the later discovery of the conflict required reversal. The court examined whether the timing alone established prejudice or whether additional facts showed the conflict affected the outcome.
Priscilla Parks obtained a substantial compensatory verdict against Pacific Mutual Life Insurance Company. The jury later added punitive damages. Pacific argued that the sequence of the large verdict followed by the punitive award proved the jury acted from passion rather than evidence. The court required proof that the punitive amount lacked a reasonable relationship to the harm rather than relying on the order of the awards.
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Perry Pratt bought Basic Inc. shares the day after a company statement. When the statement proved misleading, Perry claimed reliance on the fraud-on-the-market theory. Basic contended that the purchase timing alone did not establish that the misstatement caused the price to reflect the false information. The court examined market evidence rather than sequence to decide whether the presumption applied.
Pilar Pena was arrested during a police search filmed by a television crew. She sued the officers and the media for violating her rights. The officers argued that the presence of cameras after the warrant issued proved no Fourth Amendment violation occurred. The court required evidence that the media presence itself caused the constitutional injury rather than accepting the chronological order as dispositive.
Philip Powell installed flexible gas piping made by Omega Flex. The pipe later leaked and caused a fire. Powell claimed the product was defective because the failure followed installation. Omega Flex showed that the leak resulted from improper bending during construction. The court refused to infer defect from the sequence of installation and failure without proof that the product itself caused the harm.
No. Timing establishes only that the conduct preceded the harm. The plaintiff must still prove that the conduct was a factual and legal cause of the specific loss rather than relying on sequence alone.
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Post hoc discovery requires vacatur when the conflict is neither harmless nor trivial and undermines public confidence in the judiciary. The statute applies an objective standard that does not depend on the judge's actual knowledge at the time of the ruling.
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No. The amount of punitive damages must bear a reasonable relationship to the harm and the defendant's conduct. Sequence alone does not establish that the award was the product of passion or prejudice.
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…District Court permitted the plaintiff to proceed on her fraud-on-the-market theory. Thus, Abrams demonstrates how easily a post hoc statement will enable a plaintiff to bring a fraud-on-the-market action — even in the rare case where a plaintiff is frank or foolhardy enough to admit initially that a factor other than…