Root 2: the early evidence and later conjectures

Abstract

Historians believe that the discovery of the irrationality of √2, or, as it would have been described in classical Greek mathematics, the incommensurability of the side and diagonal of a square, was made in the period 550–410 bc. None of the early sources, however, includes a proof of the theorem, so historians have found it a happy hunting ground for conjectures. This article is drawn from the monographs of Knorr and Fowler, and was put together to show how much history of early mathematics is from the minds of historians.