Based on a mistaken belief or unsound reasoning; containing logical errors or false assumptions. Deceptive in appearance but fundamentally flawed in logic.
From Latin fallacia, meaning 'deception' or 'deceit,' derived from fallere (to deceive or fail). The word evolved from describing deliberate deception to describing any reasoning that fails to reach valid conclusions, whether intentionally or not.
Connect 'fallacious' to 'fall' - bad reasoning makes your argument fall down! In logic class, you learn about 'fallacies' - these are fallacious arguments that seem convincing but actually contain errors.
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