Copernicus and Buridan


The early modern scientists have seen further only by standing on the shoulders of giants: their predecessors.

It is the same with scientists of the present.

Copernicus’ famous book De Revolutionibus (On the Revolutions of the Heavenly Spheres) was published in April 1543  – a few days prior to his death. The book was the seminal work on the heliocentric theory and was so technically complex that only true astronomers could read it. Copernicus was known to be working on a new theory of celestial motion, according to which the earth revolves around a stationary sun, and he worked quietly on his own. For many years he ignored the pleas of at least one cardinal and two bishops to publish his ideas, until finally a young Lutheran astronomer from the University of Wittenberg, Georg Joachim Rheticus, came for an extended visit and was able to persuade Copernicus to allow his book to be printed back in Germany. Contrary to what is often said or implied, Copernicus had full freedom to pursue his ideas while working for the Church and was even encouraged to publish them.

In this book, he also discussed the rotation of the earth. He was not the first to suggest that the rotation of the earth is more parsimonious than the rotation of the entire universe [1]. Jean Buridan had already said in around 1350:

If anyone is in a moving ship and imagines that he is at rest, then should he see another ship, which is truly at rest, it will appear to him that the other ship is moved … And so, we also posit that the sphere of the sun is everywhere at rest and the earth in carrying us would be rotated. Since, however, we imagine we are at rest … the sun would appear to us to rise and then to set, just as it does when it is moved and we are at rest.  [2]

Copernicus wrote 200 years later:

When a ship sails on a tranquil sea, all the things outside seem to the voyagers to be moving in a pattern that is an image of their own. They think, on the contrary, that they are themselves and all the things with them are at rest. So, it can easily happen in the case of the earth that the whole universe should be believed to be moving in a circle [while the earth is at rest] [3]


Thank you to the fb page Just history things where the quote from J. Hannam’s book was posted!



[1]  Hannam, James. God’s Philosophers: How the medieval world laid the foundations of modern science. Icon Books Ltd, 2009. Page 275

[2] Grant, A Source Book in Medieval Science, p. 67.

[3] Copernicus, On the Revolutions of the Heavenly Spheres, p. 17

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