Sophism — Reasoning that wears the appearance of logical validity but is in fact fallacious, employed to deceive or to persuade an interlocutor by illegitimate means. The word comes from the Greek sóphisma, related to sophía (wisdom) and sophistḗs (one who teaches wisdom), though it took on a pejorative ring already in antiquity. The defining mark of a sophism is the intent to deceive: this sets it apart from a paralogism, which is a reasoning error committed in good faith, with no aim to mislead. The concept is historically tied to the Greek Sophists — itinerant teachers of rhetoric such as Protagoras and Gorgias — whom Plato and Aristotle criticized for selling the art of making the weaker argument appear the stronger, with no commitment to truth. It was Aristotle who first systematized fallacies in his treatise Sophistical Refutations (Sophistici Elenchi), distinguishing those that depend on language (such as amphiboly and equivocation) from those that do not. A classic example is the so-called “horns” sophism, attributed to Eubulides of the Megarian school: “you have what you have not lost; you have not lost horns; therefore you have horns” — where the show of correctness conceals an ambiguity in how the premises are used. Sophism thus stands close to the notions of fallacy and rhetoric: while a fallacy names the flaw in an argument and rhetoric is the art of persuasion, a sophism joins both in deliberate deceit. In contemporary logic and argumentation theory, the study of sophisms remains central to telling legitimate persuasion from manipulation.
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