Thales - Thalēs

An ancient Greek philosopher. Born in Miletus, a city in the Ionian region of Asia Minor. He is said to have been of Phoenician descent. He was the first philosopher and the founder of the Milesian school. He is said to have believed that the origin of all things (arche) was water, and that the earth floated on water. He is also reported to have believed that everything was filled with gods, but the details are unknown.

He is said to have been one of the Seven Sages, and is known for his many talents. He is said to have persuaded the Ionian cities to form a federation and place its capital in Teos to counter the power of Persia, and to have dissuaded Miletus from an alliance when King Croesus of Lydia requested it. He is also said to have predicted the solar eclipse that occurred on May 28, 585 BC, and to have divided a year into 365 days and a month into 30 days. He is said to have introduced geometry from Egypt, and is said to have discovered the theorems such as measuring the height of a pyramid from the length of its shadow, that a circle is bisected by its diameter, that the base angles of an isosceles triangle are equal, that when two straight lines intersect, the vertical angles are equal, that an angle inscribed in a semicircle is a right angle, and that a triangle can be determined if its base and base angle are given. He is said to have written a book called "Nautical Astronomy," but it seems more likely that he never wrote anything.

[Mikiya Suzuki]

"Fragments of Early Greek Philosophers" translated and edited by Mitsuo Yamamoto (1958, Iwanami Shoten)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

古代ギリシアの哲学者。小アジアのイオニア地方の町ミレトスの生まれ。フェニキア人の血を引くとも伝えられる。最初の哲学者、ミレトス学派の始祖であって、万物の元のもの（アルケー）は水であり、大地は水の上に浮かんでいると考えたと伝えられ、また、あらゆるものは神々に満ちていると考えたとも報告されるが、詳細は不明。

　彼は七賢人の筆頭にあげられる多才な人物であって、ペルシアの権力に対抗するために連邦をつくって首都をテオスに置くようイオニアの諸都市を説得したとか、リディア王クロイソスがミレトスに同盟を結ぶよう要請した際、これに応じることを思いとどまらせたとかと伝えられ、また、紀元前585年5月28日におこった日食を予言したり、1年を365日に分け、1か月を30日と定めたりしたとも伝えられる。エジプトから幾何学を取り入れた人物とされ、ピラミッドの高さをその影の長さから測定したとか、円はその直径によって二等分される、二等辺三角形の底角は相等しい、二直線が交わるとき対頂角は相等しい、半円に内接する角は直角である、三角形は底辺と底角が与えられれば決定される、といった諸定理を発見したとも伝えられる。『航海天文学』という著作があったとされるが、何も書かなかったとするほうが真実らしい。

［鈴木幹也］

『山本光雄訳・編『初期ギリシア哲学者断片集』（1958・岩波書店）』

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