The Realism of Copernicus

I've been doing some reading in preparation for teaching a course on the Copernican Revolution this Fall (currently I'm reading Alexandre Koyre's "The Astronomical Revolution"). In the process I've been struck by Copernicus' apparent motivation for developing his new system of astronomy. It wasn't so much that he was trying to devise a system that would match up better with observations (and he didn't). It wasn't that he really was convinced that the Earth moved independent of astronomical considerations (at the time you would have had to be crazy to believe that). It was that he was absolutely, utterly committed to the REALITY of uniform circular motion in the heavens. I guess this can be attributed to Platonic (or maybe Pythagorean?) influence, but he seems to have believed that uniform circular motion was the only thing that could possibly REALLY be going on up there in the skies. He states clearly that his major motivation for devising his system was to get rid of the equant, which was Ptolemy's great heresy against the Platonic (and Aristotelian) doctrine of uniform circular motion. He was so committed to ridding astronomy of equants that he was willing to consider the absurd notion of a moving Earth!

It is interesting to contrast Copernicus' metaphysical commitment to the truth of uniform circular motion with the phenomenalism of Andreas Osiander, who wrote the controversial preface to Copernicus' "De Revolutionibus". Osianders view, as stated in that preface, is that the job of astronomy is to "save the appearances" and that one should use every mathematical trick available, even one as silly as making the Earth revolve around the Sun, in order to make the calculations match the appearances of the sky. This view is actually quite sophisticated and modern, and is not much different from the logical positivism that dominated philosophy of science (and philosophy generally) during the first half of the 20th Century. But this is obviously not Copernicus' view. He is willing to throw out a very useful mathematical trick (the equant) in order to get back to what he KNOWS is the TRUE motion of the celestial bodies, namely uniform motion in a circle.

So Copernicus has the less sophisticated philosophical point of view, as well as a strong metaphysical commitment to a scientific idea that turns out to be totally wrong. And it is exactly because of this that he, rather than Osiander and others like him, revolutionized astronomy and paved the way for modern science. It turns out he didn't need to be so revolutionary. He could have gotten rid of equants and stayed with a geocentric universe by throwing in a few more epicycles (as Kepler later showed). But either he was unaware of this, or decided to give the heliocentric view a shot and became convinced of its beauty (and thus its truth, since he held that kind of Platonic view).

It is also interesting that it was Copernicus' devout commitment to uniform circular motion that led him to the first major breakthrough in astronomy since Ptolemy. But it was Kepler's ability to see past this view and consider non-uniform non-circular motion that led to the next major breakthrough. I doubt very much that Copernicus would have been pleased at what Kepler did to his astronomical system. It just goes to show that sometimes "bad" ideas lead to "good" results.