fl. c. 500 B.C.

Greek Pythagorean philosopher credited with the discovery of irrational numbers—that is, infinite decimals with no indefinitely repeating digits. Hippasus apparently discovered that the length of an isosceles triangle's shorter side must be expressed as an irrational number if the length of the two equal legs is a whole one. According to one legend, he made this discovery while on board ship with a group of other Pythagoreans, and the idea of an irrational proved so antithetical to Pythagorean views of wholeness and harmony that they threw him overboard. A conflicting tale maintains that other Pythagoreans discovered the secret of irrationals. By revealing this information to outsiders for pay, according to this version, Hippasus violated two rules of the Pythagorean society: the vow of secrecy and the prohibition against profiting from mathematical wisdom.