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Post Hoc Ergo Propter Hoc

Also Known As: Post Hoc Ergo Propter Hoc After Therefore Because False Cause (Temporal Variant)
Informal Fallacy ID: post_hoc

Definition

Post hoc ergo propter hoc ('after this, therefore because of this') is the specific fallacy of concluding that because one event preceded another, the first event caused the second. While temporal sequence is a necessary condition for causation, it is not sufficient. Many events that follow others are coincidental, caused by confounding factors, or part of a broader pattern unrelated to the preceding event.

Examples

"I wore my lucky socks and we won the game. My socks caused us to win!" or more seriously: "Crime rates dropped after we installed security cameras on Main Street, proving the cameras reduced crime." (Ignoring seasonal trends, economic changes, and other interventions.)

A CEO introduces a new office meditation room, and the following quarter profits rise. She announces at the all-hands meeting: 'The meditation room is driving our financial performance.' She ignores that a major competitor went bankrupt the same quarter, sending their clients to her company.

A city mayor bans plastic straws, and two months later the local beach water quality scores improve. Environmental groups credit the straw ban, overlooking that a large industrial plant upstream had simultaneously been fined and forced to upgrade its water filtration systems.

Formal Logic Pattern
FOL Pattern
The First-Order Logic formula representing this reasoning pattern's logical structure.
FOL (First-Order Logic) uses quantifiers (∀ = for all, ∃ = there exists), connectives (∧ = and, ∨ = or, ⇒ = implies, ¬ = not), and predicates to capture the essential form of a reasoning pattern. For example, the Ad Hominem fallacy: Person(x) ∧ HasFlaw(x) ⇒ Invalid(Claim(x)). These patterns allow automated verification of logical validity.
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Before(A, B) -> Cause(A, B)
Formal Verification:
Formal Verification
Checks whether a reasoning pattern is logically valid or invalid using an automated theorem prover.
Formal verification uses an SMT (Satisfiability Modulo Theories) solver — specifically Z3 — to mathematically check whether an argument's logical structure is valid. Each reasoning pattern is translated into First-Order Logic and tested: Can the premises be true while the conclusion is false? If yes, it's formally invalid. If no, it's formally valid. Many real-world patterns (analogies, heuristics) cannot be fully captured in formal logic — these are marked as not formally decidable, which doesn't mean they're wrong.
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Not formally decidable

Verification Steps
Verification Steps
Binary yes/no questions that an AI must answer to detect a reasoning pattern in a text.
Each of the 452 aspects has verification steps — simple yes/no questions designed to systematically detect whether a pattern appears in a text. For ad hominem: "Does the argument attack a person rather than their claim?" For false dichotomy: "Are only two options presented when more exist?" This ensures consistent, reproducible analysis.
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Binary (yes/no) questions an LLM must answer to identify this aspect:

  1. 1

    Is causation being inferred solely from temporal sequence?

    Type: binary
  2. 2

    Did event A occur before event B?

    Type: binary
  3. 3

    Is there independent evidence of a causal mechanism linking A and B?

    Type: binary
Deep Dive
The expandable detail section on each aspect page with examples, psychology, and counter-strategies.
The Deep Dive section provides in-depth information about each aspect: a real-world example showing the pattern in action, an explanation of why it works psychologically, practical advice on how to counter it, alternative names, and links to related aspects.
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Related Aspects

← related to
Cause-Effect Swap

The cause-effect swap occurs when the causal direction between two correlated phenomena is reversed. While both events are genuinely related, the arguer misidentifies which is the cause and which is the effect. This is distinct from the general false cause fallacy or post hoc reasoning in that a real causal relationship exists — it is simply inverted. The reversal often serves to support a preferred narrative or intervention.

Hierarchical Context

→ is a Informal Fallacies

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