This was a departure from the beliefs of most societies in the past, which were usually given to some measure of “ancestor worship”—the belief that all wisdom had been revealed to earlier sages and that to learn anything one should peruse their writings and find the answer in their pages. In the Islamic world, wisdom was found in the Koran and the Hadith (which consists of sayings and acts attributed to the prophet Muhammad); in the Jewish world it was the Torah, the Talmud, and the sayings of Chazal; in China, wisdom was contained in Sishu Jizhu, the four books of commentary on Confucius compiled in the 12th century. In late medieval Europe, wisdom was found in a limited number of ancient texts, above all those written by Aristotle.

The respect for classical texts started to fade away in Europe in the 16th century and went into a meltdown in the 17th, when more and more of the ancient certainties were questioned and then found to be incorrect. If the classic authorities could be wrong about so many things, why would should they be trusted about anything? The English philosopher William Gilbert, the author of a famous book on magnetism, sounded downright impudent when he wrote in 1600 that he was not going to waste time on “quoting the ancients and the Greeks as our supporters, for neither can paltry Greek argumentation demonstrate the truth more subtly nor Greek terms more effectively.”

Many of the widely believed propositions of classical science collapsed under close examination. The examples piled up. Above all, the belief that the earth was at the center of the universe, the centerpiece of ancient cosmology, withered away. But there were so many others: Aristotle had insisted that all the stars apart from the planets were immutable and fixed, but in 1572 a young Danish astronomer named Tycho Brahe observed a supernova and realized that Aristotle had been wrong. Even more striking, Aristotle had written that the tropical areas around the equator were so torrid as to be uninhabitable—but Europeans found people living and thriving in such regions in Africa, America, and India. By 1600, much of ancient wisdom had crumbled.

Worse was to come: After 1600, Europeans developed scientific instruments that allowed them to see things the ancient writers could never have imagined. No wonder they began to feel superior: Ptolemy had no telescope, Pliny had no microscope, Archimedes had no barometer. The great classical writers may have been smart and well-educated, but European intellectuals thought of themselves as equally intelligent and better informed—and thus able to see things the ancients could not. Hence, everything must be tested with real evidence, not on the say-so of authorities who had lived 1,500 years earlier. The motto of the Royal Society, which was founded in 1660 in London, was in nullius verba—“on no one’s word.” Skepticism was the taproot of all knowledge. Even the Bible itself began to be examined critically, not least by Baruch Spinoza, who cast doubt on its divine origins and saw it as just another text.