Episteme (ἐπιστήμη) — Scientific knowledge or true, grounded knowing, as opposed to doxa (opinion) and techne (practical skill). The Greek word epistēmē derives from the verb epistasthai, “to know” or “to understand,” and denotes not a belief that happens to be correct but knowledge held for reasons and able to account for its own causes. For Plato, especially in the Republic, episteme is knowledge of the Ideas or Forms — eternal, immutable, and accessible to reason alone — whereas doxa remains bound to the changing sensible world; the famous Divided Line and the allegory of the cave dramatize this ascent from opinion to knowledge. Aristotle systematizes the notion, above all in the Posterior Analytics: episteme is demonstrative, deduced from first principles that are true and necessary, and concerns what could not be otherwise. In the Nicomachean Ethics he distinguishes it as one of the intellectual virtues, separating it from both techne (productive know-how) and phronesis (practical wisdom). A classic example is geometry: it is not enough to know that a triangle’s angles sum to two right angles; one must demonstrate it from axioms. In the twentieth century, Michel Foucault reappropriates the term in The Order of Things (1966): episteme comes to name the historical, implicit ground of knowledge that defines, in each era, what can be thought, said, and held as true.
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