In lieu of an abstract, here is a brief excerpt of the content:

1 Legends say that in ancient times a secretive cult of vegetarians was led by a man who had a strange birthmark on his thigh and who taught that we should not eat beans. He believed that when a person dies, the soul can be reborn in another body, even as an animal. So he said that we should not eat animals because they might be our dead relatives or friends. And he said that he had been born five times, even before the Trojan War. And when he died his fifth death, his followers later said that he was reborn again. But why should we not eat beans? His reason: that if a bean is moistened and placed in a pitcher and buried, when we dig it up days later we will find a disturbingly familiar form growing: the head of a human child.1 We might think that none of this is true. But still, you’ve heard of the alleged fifth incarnation of this cult leader. He was Pythagoras, born sometime around 570 BCE and dying roughly seven decades later.2 People know him as the mathematician who discovered the Pythagorean theorem: that the squares on two sides of a right triangle add up to the square on its largest side. But wait. There is no evidence that he discovered that. It was already well known to the Hindus and the Chinese.3 And the Babylonians knew it more than a thousand years before Pythagoras was born on the island of Samos in the Aegean Sea. Some people say instead that Pythagoras was the first to prove that the theorem is true for all triangles. But again, is there any evidence that he did that? Lacking evidence that he really did what gives him worldwide fame, 1 TRIANGLE SACRIFICE TO THE GODS 2 T R I A NG L E SAC R I F I C E T O T H E G O D S some teachers and historians guess that Pythagoras may have been the first to prove the theorem. May have been the first? Maybe he was the fourth? Or maybe he just never did that? Maybe he was reborn seventeen times? Like other teachers, I too used to tell my students widespread stories about Pythagoras. But eventually I became uncomfortable in not knowing the roots of those stories. What if we confront such uncertainties? If Pythagoras wrote anything, none of his writings seems to have survived . What remains was written long after his death. We don’t trash it all because some of the various fragments are mutually consistent and because some reliable commentators apparently wrote some passages. Ancient sources don’t say that Pythagoras proved the hypotenuse theorem, but they do say that he didn’t eat beans and that he believed that souls are reborn. They also tell other stories. For example, that Pythagoras never laughed.4 That he infallibly predicted earthquakes, storms, and plagues. That he said that earthquakes are conventions of the dead.5 Also, that “there was such persuasion and charm in his words that every day almost the entire city turned to him, as to a god present among them, and all men ran in crowds to hear him.”6 And, that when he and his associates once crossed the river Nessus, Pythagoras spoke to the river, and it loudly replied: “Hail, Pythagoras!”7 One ancient poem says that Pythagoras was the son of the god Apollo, who visited his mother: “Pythagoras, whom Pythias bore for Apollo, dear to Zeus, she who was the loveliest of the Samians.”8 But is any of this true? What can we believe about a mysterious man who lived ages ago? And why does it matter? It matters because by trying to replace legends with history we exercise critical thinking. Some people don’t want to discard a familiar simple story. But by seeking evidence we learn to pinpoint falsehoods; so Albert Einstein remarked: “Whoever is careless with the truth in small matters cannot be trusted in important affairs.”9 We tend to care about long-dead people to the extent that we find ourselves reflected in them. Math teachers care about Pythagoras mainly because they construe him as an ancient role model, a hero who got something right, a genius who recognized the importance of mathematics. Likewise, vegetarians admire Pythagoras because he said that we should not eat animals. Musicians admire him because he allegedly discovered numerical ratios...

Share