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mathematics

Geometric Proof (QED)

ὅπερ ἔδει δεῖξαι

Every Greek proof followed one fixed script — state it, draw it, build it, argue it — and sealed it with 'which was to be proved.'

Greek geometry turned the proof into a fixed literary form: state the proposition, set out the figure, make the needed construction, advance the argument, and close with 'that which was to be demonstrated' (in Latin, quod erat demonstrandum, or QED) — or, for a construction, 'that which was to be done.' Euclid of Alexandria (c. 300 BCE) is the great exemplar, but the formula and structure were shared across Greek mathematicians such as Archimedes and Apollonius. This template set the public standard of mathematical rigor for two thousand years.

Where this idea shows up

18 Greek sources

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