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Hippasus of Metapontum (; , ''Híppasos''; fl. 5th century BC), was a Pythagorean philosopher. Little is known about his life or his beliefs, but he is sometimes credited with the discovery of the existence of irrational numbers. The discovery of irrational numbers is said to have been shocking to the Pythagoreans, and Hippasus is supposed to have drowned at sea, apparently as a punishment from the gods for divulging this. However, the few ancient sources which describe this story either do not mention Hippasus by name (e.g. Pappus)〔http://www.wilbourhall.org/pdfs/pappus/PappusBookX.pdf〕 or alternatively tell that Hippasus drowned because he revealed how to construct a dodecahedron inside a sphere. The discovery of irrationality is not specifically ascribed to Hippasus by any ancient writer. Some modern scholars though have suggested that he discovered the irrationality of √2, which it is believed was discovered around the time that he lived. ==Life== Little is known about the life of Hippasus. He may have lived in the late 5th century BC, about a century after the time of Pythagoras. Metapontum in Italy (Magna Graecia) is usually referred to as his birthplace,〔Simplicius, ''Physica'' 23.33〕〔Aetius I.5.5 (Dox. 292)〕〔Clement of Alexandria, Protrepticus 64.2〕 although according to Iamblichus some claim Metapontum to be his birthplace, while others the nearby city of Croton.〔Iamblichus, ''Vita Pythagorica'', 18 (81)〕 Hippasus is recorded under the city of Sybaris in Iamblichus list of each city's Pythagoreans.〔Iamblichus, Vita Pythagorica, 34 (267)〕 He also states that Hippasus was the founder of a sect of the Pythagoreans called the ''Mathematici'' () in opposition to the ''Acusmatici'' ();〔Iamblichus, ''De Communi Mathematica Scientia'', 76〕 but elsewhere he makes him the founder of the ''Acusmatici'' in opposition to the ''Mathematici''.〔Iamblichus, ''Vita Pythagorica'', 18 (81); cf. Iamblichus, ''In Nic.'' 10.20; ''De anima'' ap. Stobaeus, i.49.32〕 Iamblichus says about the death of Hippasus :''It is related to Hippasus that he was a Pythagorean, and that, owing to his being the first to publish and describe the sphere from the twelve pentagons, he perished at sea for his impiety, but he received credit for the discovery, though really it all belonged to HIM ( for in this way they refer to Pythagoras, and they do not call him by his name).'' According to Iamblichus (ca. 245-325 AD, 1918 translation) in ''The life of Pythagoras'', by Thomas Taylor :''There were also two forms of philosophy, for the two genera of those that pursued it: the ''Acusmatici'' and the ''Mathematici''. The latter are acknowledged to be Pythagoreans by the rest but the Mathematici do not admit that the Acusmatici derived their instructions from Pythagoras but from Hippasus. The philosophy of the Acusmatici consisted in auditions unaccompanied with demonstrations and a reasoning process; because it merely ordered a thing to be done in a certain way and that they should endeavor to preserve such other things as were said by him, as divine dogmas. Memory was the most valued faculty. All these auditions were of three kinds; some signifying what a thing is; others what it especially is, others what ought or ought not to be done.'' (p. 61) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hippasus」の詳細全文を読む スポンサード リンク
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