Was Galileo a plagiarizer?

If we where to apply to the works of Galileo the general standards of plagiarism that we conform to today at our local institutions, would he be considered a plagiarizer?

Take, for instance, the mean speed theorem. From Wikipedia:

The now published sources prove to us, beyond contention, that the main kinematical properties of uniformly accelerated motions, still attributed to Galileo by the physics texts, were discovered and proved by scholars of Merton college.... In principle, the qualities of Greek physics were replaced, at least for motions, by the numerical quantities that have ruled Western science ever since. The work was quickly diffused into France, Italy, and other parts of Europe. Almost immediately, Giovanni di Casale and Nicole Oresme found how to represent the results by geometrical graphs, introducing the connection between geometry and the physical world that became a second characteristic habit of Western thought ..

Yet Galileo makes no mention of these predecessors on whose work his is based. He even comes very nearly to claiming that these were his own inventions.

So my question is: would such a vagrant disregard of proper crediting be considered plagiarism if this piece of academia was to happen today?

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    $\begingroup$ This question is stated in a needlessly argumentative way. You're talking about an era when scientific journals didn't exist, and there was no concept similar to the modern idea of citing a reference in a paper. Publishing your work was not even something that was expected or required. In some cases, e.g., the cannonball dropped from the mast of a ship, Galileo did cite previous claims by people who said they'd done the experiment, and he cited them in order to say that they must have been lying, because their result wasn't what actually happened when Galileo did it himself. $\endgroup$
    – user466
    Commented May 12, 2015 at 15:55
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    $\begingroup$ Even in the modern times he would not be considered plagiarizer, until you PROVE that he read these results and and appropriated them. Rediscoveries permanently happen and important thing is almost always discovered many times by many people. The question "who was the first" which is so popular on this site is in most cases meaningless. $\endgroup$ Commented May 14, 2015 at 0:05

2 Answers 2


See Heytesbury and the Physical Sciences and Nicole Oresme for detailed information about the so-called Oxford Calculators and their contribution (mainly) to mathematics.

The issue is not so clearly assessed by modern historiography:

There has been some discussion of the meaning of the work of Heytesbury and the other Calculators for the development of the physical sciences. Here it must first be noted that Heytesbury did not think of himself as doing natural science. [...] There is no direct evidence that Galileo knew of or used their results, but it is apparent from the presence of this work in the logic curriculum in Italy that these results were in the air.

You must at least take into account that medieval philosphical treatises were not available in print during XVI and XVII Centuries ...

For a detailed discussion of Galileo (and Descartes) works on kinematics and possible connections with the so-called Merton Rule (the medieval forerunner of mean-speed theorem) see :

See also:

At Oxford, the so-called Calculators, many of them associated with Merton College, devised a number of quantitative methods for the logical examination and description of qualitative change and motion. [...] Another was the mean-speed theorem, which equated the overall speed of a uniformly accelerated motion to its mean, or middle, degree of speed. Usually attributed to William Heytesbury (fl.1335), the mean-speed theorem was widely used and is found in the works of other fourteenth-century Mertonians.

These fourteenth-century ideas continued to be taught in various forms through the sixteenth century, when they finally fell under the criticism of the humanists, who ridiculed them for their trivial logic-chopping and their authors for their barbarous Latin and bizarre names. Their works lay unread until the French physicist and historian of science Pierre Duhem (1861–1916) rediscovered them at the end of the nineteeenth century.

Subsequent scholars often tacitly assumed some degree of continuity between late-medieval and early-modern science without necessarily adhering to the whole Duhem thesis. [...] Ernest A. Moody, however, suggested that Galileo’s early ideas concerning motion were not derived from the fourteenth century Mertonians and Parisians but from anti-Aristotelian alternatives reported in the sixteenth-century sources that Galileo is known to have read. Since these sources contained little about such fourteenth-century developments in physics as the mean-speed theorem, Moody suggested that Galileo later rediscovered them on his own.


By this standard why single out Galileo? Euclid "plagiarized" Elements, there isn't a single theorem in it that can be reliably attributed to him, and there are entire books that can be attributed to early Pythagoreans, Eudoxus or Theaetetus. In the whole 13 books he does not credit a single person by name. Descartes "plagiarized" analytic geometry, after all Oresme and Casale were drawing coordinate graphs before him. And Newton sure "plagiarized" most of Principia, the first law of motion is due to Galileo, the second one was formulated by Huygens (in the integrated form), and the inverse square law was discussed by many astronomers in the 17th century, not all of whom he credited. The same with calculus, Archimedes was finding areas and volumes, and Apollonius finding tangents in antiquity, not to mention Fermat and others in the 17th century, and even the "fundamental theorem of calculus" was already proved geometrically by Newton's teacher, Barrow.

In all cases the difference is between isolated ideas and a systematic theory. Galileo not only derived the time squared law without the mean speed theorem, but put it into a broader context of new mechanics, and applied it to physical reality, none of which Merton school, or even Oresme, did. In a 1639 letter he writes:"But in this, I may say, I have been lucky; for the motion of heavy bodies, and the properties thereof, correspond point by point to the properties demonstrated by me". Here is from Screnes's essay:

"Galileo’s calculations relied on an ancient Greek theory of proportion that was not preserved in standard medieval translations of Euclid, and didn’t become available until a better translation was made in 1543. Recent research confirms his claim that he derived the law of acceleration arithmetically, independently of experiment. His derivation was also independent of the mean speed theorem of the Merton school... In the case of the 14th century mathematicians at Oxford, a mathematical treatment of the concept of uniform acceleration was developed from which the times-squared law can be derived directly. No one in the Merton school actually derived the law, however, and there was little concern for applying the mathematics to physical systems." (boldface mine)

Science is a multi-generational enterprise. Some of this sentiment comes from the popular but unfortunate manner of presenting its history as a sequence of discoveries and inventions that came out of nothing in a flash of insight. Every idea has precursors, and every genius has predecessors. Not all of them can be cited, or even clearly identified, so in a sense everybody is a "plagiarizer". When Newton said that he was "standing on the shoulders of giants" he unintentionally admitted it (the intention was a slight at Hooke's small stature).


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