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Who really said it

Measure what is measurable, and make measurable what is not so

Not Galileo — Thomas-Henri Martin, describing him in 1868 Thomas-Henri Martin 1813–1884 · French Hellenist, historian of science and dean of the Faculty of Letters at Rennes
Disputed Rights unconfirmed

Wikiquote files the line among Galileo’s misattributed quotations ↗ and traces it, following Andreas Kleinert’s 2009 article in NTM, to two nineteenth-century French scholars. We read both books. The full two-part sentence first appears in Th.-Henri Martin’s Galilée (Paris: Didier, 1868), p. 289 ↗ — and not as a quotation: Martin writes “Il déclare que dans tous ces phénomènes il faut mesurer tout ce qui est mesurable, et tâcher de rendre mesurable tout ce qui ne l’est pas directement,” in indirect speech, in roman type, with no quotation marks anywhere near it. It is a historian’s summary of Galileo’s method that later readers promoted into Galileo’s own words.

Last verified 22 Aug 2026 · how we verify · spot an error?

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Disputed credit — copy with the correction

“Measure what is measurable, and make measurable what is not so” Not Galileo. The sentence is Th.-Henri Martin's, written about Galileo in indirect speech and never in quotation marks: "Il déclare que dans tous ces phénomènes il faut mesurer tout ce qui est mesurable, et tâcher de rendre mesurable tout ce qui ne l'est pas directement," Galilée : les droits de la science et la méthode des sciences physiques (Paris: Didier, 1868), p. 289. A shorter form, without the second clause, is in Cournot, De l'origine et des limites de la correspondance entre l'algèbre et la géométrie (Paris: L. Hachette, 1847), p. 375. Traced by Quotle.info.

The slide-ready mistake: crediting this to Galileo Galilei. Use the credit shown above instead.

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In context

Evoking the world of Thomas-Henri Martin — French Hellenist, historian of science and philosopher. Theme: "Measure what is measurable, and make measurable what is not so". Atmospheric and restrained, cinematic directional light, a muted period-appropriate palette, fine grain and texture. Compose with generous empty space for the quote and a small credit line. No lettering in the image itself.

Minimalist

Minimalist editorial slide for the quote "Measure what is measurable, and make measurable what is not so". Clean background, a single muted accent color, generous negative space, subtle paper or linen texture, no literal illustration — let the words carry it. Reserve clear space for a serif quote and a small credit line. No lettering in the image itself.

Provenance

A summary that turned into a quotation

Work
Galilée : les droits de la science et la méthode des sciences physiques
Author
Th.-Henri Martin (1813–1884)
Published
Paris: Didier, 1868
Located
p. 289, running head “GALILÉE”
Form
Indirect speech — Martin’s own sentence about Galileo, not a quotation of him

… il sait que les phénomènes purement physiques doivent se réduire à des mouvements, les uns perceptibles pour nos sens, les autres imperceptibles pour nous à titre de mouvements appréciables. Il déclare que dans tous ces phénomènes il faut mesurer tout ce qui est mesurable, et tâcher de rendre mesurable tout ce qui ne l’est pas directement. Il ne s’agit donc pas de poser des principes, les uns métaphysiques, les autres mathématiques, puis d’essayer d’en conclure a priori quelles doivent être les lois physiques…

Transcribed from the 1868 scan. The three words that matter are the first three: Il déclare que — “He declares that.” Everything after them is Martin’s prose about Galileo, in his own French, and it is set in ordinary roman type without a single quotation mark. In English the sentence reads roughly: he declares that in all these phenomena one must measure everything that is measurable, and try to make measurable everything that is not directly so.

Martin, Galilée (1868), p. 289, at the Internet Archive

How we verified this

  • English Wikiquote lists the line under Galileo’s misattributed quotations ↗ and names Antoine-Augustin Cournot and Thomas-Henri Martin as the real source, citing Andreas Kleinert, “Der messende Luchs: Zwei verbreitete Fehler in der Galilei-Literatur,” NTM Zeitschrift für Geschichte der Wissenschaften, Technik und Medizin 17, no. 2 (May 2009): 199–206.
  • German Wikiquote gives Kleinert’s finding in more detail ↗: there is no evidence for the sentence in Galileo’s writings; the earliest occurrence is Martin’s of 1868, with a shorter precursor in Cournot of 1847; and it was taken up and spread by Wilhelm Dilthey and Hermann Weyl. Kleinert’s article itself is behind a paywall we could not reach, so that chain of transmission rests on Wikiquote’s summary of it, not on our own reading.
  • We read Martin’s page rather than the summary of it. Page 289 of the 1868 scan ↗ carries the sentence in indirect speech — “Il déclare que…” — unquoted, in a paragraph reconstructing how Galileo thought about measurement.
  • And we read Cournot’s. De l’origine et des limites de la correspondance entre l’algèbre et la géométrie (Paris: L. Hachette, 1847), p. 375 ↗ has only the first half: true physics was founded, Cournot writes, the day Galileo conceived the idea of assigning to experiments “pour objet immédiat la mesure de tout ce qui peut être mesurable dans les phénomènes naturels.” The famous second clause — making measurable what is not — is not there.

Both documented sources are long out of copyright: Cournot’s book of 1847 ↗ and Martin’s of 1868 ↗ are freely readable at the Internet Archive. The English sentence at the top of this page is a different matter — it is an anonymous rendering of Martin’s French by a translator nobody has identified, of a date nobody has established, so we assert no rights status for it rather than guess one.

Rights status is our research, not legal advice — and copyright varies by country and edition. For commercial or published use, confirm with the rightsholder. See terms.

Fact-check

Often misattributed

This is the tidiest one-line statement of the experimental method anyone has written, which is why it has been handed to the man who invented the method. He did not write it.

Galileo Galilei Misattributed

The sentence occurs nowhere in his works. English Wikiquote files it under “Misattributed” ↗ and German Wikiquote states flatly that there is no evidence for it in his writings ↗, both citing Kleinert’s 2009 study.

Th.-Henri Martin, Galilée (1868), p. 289

Read from the scan ↗: Martin writes it as his own summary, in indirect speech, without quotation marks. He is describing what Galileo declares, in the way any historian describes a subject’s position — and the sentence was later lifted out of his paragraph and put between quotation marks.

Antoine-Augustin Cournot, 1847 Ancestor, not the author

On p. 375 of his 1847 book ↗ Cournot credits Galileo with making experiments aim at “the measurement of everything that can be measurable in natural phenomena.” That is the first clause and only the first clause; the paradoxical half that makes the line quotable is Martin’s addition twenty-one years later.

Wilhelm Dilthey and Hermann Weyl Popularizers, not authors

German Wikiquote, summarising Kleinert, says the line was taken up and circulated by Dilthey and Weyl ↗. We could not read Kleinert’s article ourselves — it sits behind a publisher paywall this build could not reach — so this row reports Wikiquote’s account of it rather than a source we opened.

The idea is genuinely Galileo’s. The sentence is Martin’s, and on the page where it first appears it is not even in quotation marks ↗.

Context

Why it mattered

Nineteenth-century France was busy deciding what the scientific method was, and Galileo was the figure it argued through. Cournot in 1847 and Martin in 1868 were both making the same case — that what separated Galileo from everyone before him was not experiment, which Bacon also urged, but measurement — and each wrote a summary sentence to carry it.

Martin’s summary was better than Cournot’s because he added the second half. Measuring what can be measured is only good practice; undertaking to make measurable the things that are not is a programme, and it is what actually happened over the following three centuries, from the thermometer to the questionnaire. A sentence that good does not stay a footnote in a French monograph. It gets promoted.

Il déclare que… — three words that make the rest a summary, not a quotation.

Read the full story

The promotion is visible in what happened to the two clauses. Cournot’s version, on p. 375 of his 1847 book on algebra and geometry ↗, is embedded in an argument about which parts of pure mathematics deserve to be called useful; it names Galileo but claims no words for him. Martin’s, twenty-one years later on p. 289 ↗, is a compact paraphrase in a chapter on method. Neither man was quoting. Somewhere between them and the modern slide deck the framing verb fell away, the quotation marks arrived, and the sentence acquired an author who had been dead for 226 years.

It is worth saying what this page is not claiming. Galileo really did insist on measurement, and really did build the instruments to do it — Martin’s own paragraph credits him with having “posé le principe” and invented the necessary instruments. The objection is narrower and it is about evidence: a sentence in quotation marks with a famous name under it is a claim about what a specific person wrote, and this one cannot be met. Martin was a Hellenist and historian of science ↗, and the words are his.

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Filed under

More provenance-checked quotes on the same theme, each with its reuse status.

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Dig deeper

Trusted places to keep pulling the thread — primary archives, fact-checks, and scholarship. We show how we used each one before you leave.

Wikiquote: Galileo Galileien.wikiquote.org

Files the line under “Misattributed” and names Cournot and Martin as its real source, citing Kleinert’s 2009 article in NTM.
Wikiquote (German): Galileo Galileide.wikiquote.org

The fuller version of Kleinert’s finding: no evidence in Galileo’s writings, Martin 1868 the earliest, Cournot 1847 the shorter precursor, Dilthey and Weyl the popularisers.
Martin, Galilée (Paris: Didier, 1868)archive.org

The scanned first edition. Page 289 carries the sentence in indirect speech, in a chapter on Galileo’s method.
Cournot, De l’origine et des limites… (1847)archive.org

The scanned 1847 volume. Page 375 has the half-version: experiments aimed at “la mesure de tout ce qui peut être mesurable dans les phénomènes naturels.”
Wikipédia: Thomas-Henri Martinfr.wikipedia.org

The author of the sentence: Bellême 1813 to Rennes 1884, Hellenist, historian of science, dean of the Faculty of Letters at Rennes. There is no English article on him.
Wikipedia: Antoine Augustin Cournoten.wikipedia.org

The mathematician and philosopher (1801–1877) whose 1847 book carries the earlier, shorter form of the idea.

The author

About Thomas-Henri Martin

Thomas-Henri Martin

1813–1884 · French Hellenist, historian of science and philosopher

Thomas-Henri Martin was born at Bellême in 1813, entered the École normale in 1831, and took his doctorate in 1836 with a Latin thesis on Spinoza. He spent his career at Rennes, as professor of ancient literature and eventually dean of the Faculty of Letters, and made his name on the boundary between classical scholarship and the history of science — a long edition of and commentary on Plato’s Timaeus, studies of ancient astronomy, and in 1868 Galilée : les droits de la science et la méthode des sciences physiques. He died at Rennes in 1884, and the one sentence of his that everybody knows is filed under somebody else’s name.

For writers & researchers

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The primary source (Chicago)

Th.-Henri Martin, Galilée : les droits de la science et la méthode des sciences physiques (Paris: Didier, 1868), 289: “Il déclare que dans tous ces phénomènes il faut mesurer tout ce qui est mesurable, et tâcher de rendre mesurable tout ce qui ne l’est pas directement.” Written in indirect speech, unquoted. Earlier half-form in Antoine-Augustin Cournot, De l’origine et des limites de la correspondance entre l’algèbre et la géométrie (Paris: L. Hachette, 1847), 375.

This verification page

Quotle.info. “Who really said ‘Measure what is measurable, and make measurable what is not so’?” Last verified 22 Aug 2026. https://quotle.info/who-said/measure-what-is-measurable-and-make-measurable-what-is-not/

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