Hippasus (Ἵππασος)

Ancient biographical and philosophical sources present Hippasus chiefly as a Pythagorean of Magna Graecia (often associated with Metapontum and variously placed in chronological relation to Pythagoras). Later accounts and exegetical traditions attach to him the role of the member who divulged secret numerical or geometric knowledge (accounts vary between the disclosure of irrational magnitudes and methods for constructing a dodecahedron), and these traditions narrate that such divulging led to expulsion or legendary drowning as divine or communal punishment. Separately, the name Ἵππασος occurs several times in mythic catalogues as distinct, ordinary characters (a centaur slain at Pirithous's wedding; a son of Priam; a Thessalian warrior; a son of Ceyx), without forming a single unified origin myth.

The sources provide no sustained physical or supernatural description for Hippasus the philosopher; he is treated as a mortal historical figure. The mythic name-bearers listed in epic catalogues are recorded only by role and fate (for example, a centaur killed by Theseus) and lack distinctive physical description in the cited materials beyond their conventional mythic types.

Attributions in the sources are intellectual and social rather than supernatural. A scholium on Plato's Phaedo attributes early musical experimentation to Hippasus — the use of bronze disks to determine musical ratios (4:3, 3:2, 2:1). Later biographical traditions associate him (variably and inconsistently) with the discovery or disclosure of incommensurable magnitudes (irrational numbers) or with techniques for inscribing a regular dodecahedron in a sphere. Ancient testimonies disagree about exact authorship, and some sources describe the act of disclosure as an impious breach of Pythagorean secrecy, bringing legendary punishment (expulsion or drowning).