Galileo Galilei

Where the senses fail us, reason must step in. I could not see the Earth move. Nobody can. But I could build a logical structure from observable phenomena — pendulums, falling bodies, projectile motion — and the structure revealed what the senses concealed.

I have been placed under house arrest for the rest of my life for stating that the earth moves around the sun. The Inquisition has my signature on the recantation. What they do not have — and cannot have — is my conviction. The evidence does not change with the signature. The earth moves. I have seen Jupiter's moons. I have seen the phases of Venus. I have...

And yet it moves. Eppur si muove. I am said to have muttered this under my breath after recanting before the Inquisition in 1633 — recanting my demonstration that the Earth orbits the Sun. Whether I said it or not, I thought it. The Earth does move. The evidence of the telescope, the phases of Venus, the moons of Jupiter, the parallax of celestial bodies —...

Eppur si muove — and yet it moves. I may not have said this in the courtroom. But I thought it. The Inquisition can determine what I say publicly; it cannot determine what the Earth does.

The authority of a thousand is not worth the humble reasoning of a single individual. I put this principle against the universities, the cardinals, and the Pope. The result was house arrest at Arcetri for the last nine years of my life. I do not regret the principle.

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. I was told that the moons of Jupiter cannot exist because Aristotle knew of only seven celestial bodies. I pointed the telescope at Jupiter. The moons were there. The argument from authority had failed; the argument from evidence had won. That is...

The Dialogo was published in February 1632. By October I had been summoned to Rome. The Inquisition said I had violated the injunction of 1616 by defending the Copernican system. I said I had merely presented both sides with fairness. They were not persuaded.

The book's title page shows three figures in conversation: Aristotle, Ptolemy, and Copernicus....

And yet it moves. The universe cannot be read until we have learnt the language in which it is written. It is written in mathematical language, and its characters are triangles, circles, and other geometrical figures.

The book of nature is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures, without which it is humanly impossible to understand a single word of it; without these, one wanders about in a dark labyrinth. Aristotle read the book of nature with his eyes. I have read it with a telescope and with...

The book of nature is written in the language of mathematics. When I dropped two balls of unequal weight from the Tower of Pisa — or rather when I conducted the equivalent experiments along inclined planes, which is more easily measured — I found that they fell at the same rate, regardless of weight. Aristotle had said the heavier would fall faster. He was...

I have never met a man so ignorant that I couldn't learn something from him. All truths are easy to understand once they are discovered; the point is to discover them first.

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. The Bible tells us how to go to heaven — not how the heavens go.