Epistēmē

Epistēmē (ἐπιστήμη) is knowledge in the fullest sense — secure, well-grounded understanding, the kind that can explain and justify itself. It is the root of our 'epistemology', the study of knowledge, and seems to derive from epistasthai, literally 'to stand over' a matter, as one who has mastered it and surveys the whole.

Knowledge against opinion

Plato drew a sharp line between epistēmē and doxa, mere opinion. Opinion may happen to be true, but it is unstable and cannot give the reason why; knowledge is bound fast by an account (logos) of its cause, and so cannot be shaken. Because its objects must themselves be stable, true knowledge is of the eternal Forms, not of the shifting things of sense — it occupies the upper reaches of the Divided Line.

Science and its limits

Aristotle refined epistēmē into demonstrative science: knowledge of necessary truths drawn from first principles. Yet he too marked its boundaries, distinguishing this theoretical knowing from the practical wisdom (phronēsis) that guides action and the skill (technē) that guides making. Not everything worth knowing takes the form of a science.