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Formal fallacy

A compact thinking tool for spotting patterns and avoiding mistakes.

  1. The useful idea

    In logic and philosophy, a formal fallacy is a pattern of reasoning with a flaw in its logical structure (the logical relationship between the premises and the conclusion).

  2. How it works

    A formal fallacy is contrasted with an informal fallacy.

  3. Why it matters

    A formal fallacy must have an invalid logical form and thus be unsound.

Use Formal fallacy as a quick check before trusting your first conclusion.

Use Formal fallacy as a quick check before trusting your first conclusion.

Test your recall

Which idea belongs to the explanation of Formal fallacy?

  • The useful idea — correct
  • How it works
  • Why it matters

In logic and philosophy, a formal fallacy is a pattern of reasoning with a flaw in its logical structure (the logical relationship between the premises and the conclusion).

EvergreenLast verified 2026-07-19

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