Galileo Quotes: 25 Sayings and Which Ones He Really Said

25 Sayings of Galileo Galilei, With a Note on “And Yet It Moves”

Galileo Galilei is one of the most quoted scientists in history, and also one of the most misquoted. Of the 25 sayings that circulate under his name in lists like this one, about half can be traced to his own books and letters. The rest are later summaries, lines spoken by characters in his dialogues, sayings borrowed from other people, or inventions with no source at all. His most famous line, "And yet it moves", was probably never said.

This guide groups the 25 sayings by where they really come from, explains what Galileo meant in context, and flags the ones you should not quote as his.

Who Galileo was, in brief

Galileo was born in Pisa on 15 February 1564 and died at Arcetri, near Florence, on 8 January 1642, aged 77. The portrait above is the well-known painting by Justus Sustermans. He trained in mathematics, taught at Pisa and Padua, and in the late 1590s devised an improved geometric and military compass for gunners and surveyors.

His fame rests on a few extraordinary years. After hearing of the Dutch spyglass in 1609 he built better telescopes of his own. He saw that the Moon has mountains and valleys, found four moons orbiting Jupiter in January 1610 (still called the Galilean moons), observed the phases of Venus from late 1610 and studied sunspots. He published his first discoveries in March 1610 in Sidereus Nuncius, "The Starry Messenger".

Those observations made him a public champion of the Copernican view that the Earth moves around the Sun. His 1632 Dialogue Concerning the Two Chief World Systems led to a trial by the Roman Inquisition in 1633. He was found "vehemently suspect of heresy", the book was banned, and he spent the rest of his life under house arrest, from 1634 at his villa in Arcetri. There he wrote Two New Sciences (1638), on motion and the strength of materials, published in Holland to escape censorship. He was completely blind by 1638.

Sayings from his writings on science and faith

Several of the best quotes come from the Letter to the Grand Duchess Christina, written in 1615 and printed only in 1636. In it Galileo argued that God is the author of both Scripture and nature, so the two cannot truly contradict each other. Where careful observation clashes with a traditional reading of the Bible, he said, the reading should be reconsidered.

No. 1 (reason as a gift): from the Letter. He wrote that he did not feel bound to believe "the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use."
No. 12 (heaven and the heavens): also from the Letter, but Galileo was quoting someone else, almost certainly Cardinal Cesare Baronio: the Holy Spirit's aim is to teach "how one goes to heaven and not how heaven goes." The popular wording about the Bible is a modern rephrasing.
No. 24 (no limits to human ingenuity): his rhetorical question about who could claim that everything knowable is already known appears in the Letter, collected in Stillman Drake's Discoveries and Opinions of Galileo.
No. 9 (heresy and proof): the idea that it harms souls to make it heretical to believe what has been demonstrated fits his arguments of 1615–16, but we could not confirm the exact wording in a primary source, so treat it as attributed.

Lines from his books on the heavens and on motion

No. 4 (the Moon): close to the opening of The Starry Messenger (1610), where he describes the delight of seeing the Moon's body up close through his telescope.
No. 11 (the book of the universe): from The Assayer (1623), which he called his scientific manifesto. The universe, he said, can only be read by someone who knows its language, and "it is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures."
No. 10 (names follow things): from his letters on sunspots (1612–13), also in Drake's Discoveries and Opinions of Galileo. His point: we should fit words to reality, not bend reality to fit our labels.
No. 23 (large and small are relative): from the Dialogue Concerning the Two Chief World Systems, where words like "immense" and "tiny" are shown to depend on what you compare a thing with.
No. 15 (the Sun and the grapes): a rendering of a passage spoken by Salviati, the character who voices Galileo's views in the same Dialogue. It is an idea from the book, but strictly the words belong to a fictional speaker.
No. 7 (an experiment examined more carefully) and No. 25 (a gateway to a new science): both are translations of passages in Two New Sciences (1638). In the second, he predicts that sharper minds will push his new science of motion much further, which is exactly what Newton did.

From his letters and notes

No. 5 (to Kepler): Galileo's complaint to Johannes Kepler about scholars who would not even look through the telescope comes from a letter usually dated August 1610. It is collected in Italian editions such as Frammenti e lettere, and is one of the most human moments in his correspondence: he asks whether he should laugh or cry.
No. 2 and No. 8 (one spark of reason): these are the same saying, the second simply shortened. The thought that the authority of a thousand opinions weighs less than one person's sound reasoning is commonly credited to his notes and fragments, again via Frammenti e lettere, though English wordings vary widely.
No. 6 and No. 16 (the less people know, the more they argue): another pair, short and long versions of one passage about how ignorance breeds confident arguments while knowledge breeds caution. It is widely quoted from English translations of his polemical writings; we could not pin down the exact page, so cite it with care.

Sayings he probably never said

The following lines are popular, but no one has traced them to anything Galileo wrote. Quote them, if at all, as "often attributed to Galileo".

No. 3, that passion gives birth to genius: no known source.
No. 13, that good reasoners are outnumbered by bad ones: no known source.
No. 14, that denying scientific principles lets you defend any paradox: no known source.
No. 17, about never meeting a man too ignorant to learn from: it appears in twentieth-century popular history, not in his works.
No. 18, wine as sunlight held together by water: a modern polishing of a remark reportedly recorded long after his death, in which he compared wine to light mixed with moisture.
No. 20, that truths are easy once discovered: found in modern self-help and business books, not in his writings.
No. 21, that you cannot teach a man anything but only help him find it within himself: no known source.
No. 22, "measure what is measurable": often printed on science posters, but not found in his works; it appears to be a later summary of his approach.

"And yet it moves": the story behind No. 19

According to legend, after being forced to recant in 1633, Galileo muttered Eppur si muove, "and yet it moves", meaning the Earth. The story first appears in print in Giuseppe Baretti's The Italian Library, published in London in 1757, more than a century after his death. Galileo's first biographer, his student Vincenzo Viviani, does not mention it, and the trial records do not contain it.

A painting bought in 1911, once thought to be by Murillo and dated to the 1640s, shows the words on a prison wall. It closely copies an 1837 painting, and many experts doubt it is from the seventeenth century at all. Historians therefore treat the remark as a legend, however well it captures his views. The old version of this list also said he recanted under torture. There is no evidence that he was tortured: he was tried, interrogated, made to abjure and confined to his home.

How to use Galileo's words well

If you want a Galileo quote for a speech, essay or classroom, choose one tied to a named work: the Letter to Christina, The Starry Messenger, The Assayer, the Dialogue or Two New Sciences. Name the work, and note that you are using an English translation. Avoid the polished one-liners that never give a source.

The real Galileo is more interesting than the poster version anyway. He was combative, funny and often sarcastic, and his best lines come wrapped in long arguments about evidence, motion and the limits of authority. Reading a few pages of the originals in a good translation is the surest way to quote him correctly.

Related Books:
The Essential Galileo

Discoveries and Opinions of Galileo

Selected Writings (Oxford World's Classics)

On Sunspots

Thus Spoke Galileo: The great scientist's ideas and their relevance to the present day

Galileo's Logical Treatises: A Translation, with Notes and Commentary, of his Appropriated Latin Questions on Aristotle's Posterior Analytics Book II ... in the Philosophy and History of Science)

Galileo's Logic of Discovery and Proof: The Background, Content, and Use of His Appropriated Treatises on Aristotle's Posterior Analytics (Boston Studies in the Philosophy and History of Science)

Sources: Wikipedia: Galileo Galilei; Wikipedia: Letter to the Grand Duchess Christina; Wikipedia: And yet it moves.

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