Aristotle vs. Ptolemy
We point out an uneasy tension beneath an apparent unity.
We have mentioned before our uneasiness with the simplifications our tutor has encountered in the teaching of history. Of course, the first time through, one cannot swamp the student with myriad details. The rules must be taught before the exceptions. Unfortunately, unless the student goes on to study history in an advanced way, the exceptions may never show up at all. Mostly, this is not an important failing (unless one goes on to make pronouncements based on simplified history). But recently we’ve been doing a bit of historical research that highlights an important detail we’ve mentioned before.
Ancient Greek philosophy and science, at least in their final form as passed on to the Romans and then the Middle Ages, are generally presented as a monolithic whole. There may be some discussion about Epicurean ethics as opposed to the Stoic kind, but the geocentric universe of four elements was generally agreed. Aristotle had concluded on philosophical grounds that the planets (which included the Sun and Moon) had to move in perfect circles at uniform speeds. Ptolemy built a quantitative theory of planetary motion out of these ideas. And so the picture remained for more than a thousand years.
But not quite. In order to match the actual motions of the planets, Ptolemy had to have them move in circles offset from the center of the Earth, with a motion uniform only as seen from another point offset in the other direction. This “saving the phenomena” was championed by anyone who was concerned with where the planets actually were. (It must be said that the main motivation in Medieval times was astrology; actual systematic observations were extremely rare, though they were done in Muslim lands.) The philosophers abhorred the idea as a sort of sell-out. This tension remained for centuries, and could not be resolved within the structure of philosophy as it stood then.
There was in fact some progress made during that time, stemming from criticism of both Aristotelian physics and Ptolemaic astronomy. The Scientific Revolution did not have to start from an entirely clean slate. But we emphasize the sheer difficulty of doing anything at this level in the Middle Ages. When almost no one could read or write, the number of people who could understand the mathematics involved amounted to just a handful at any one time. Supposing you were one of them, the nearest manuscript of either author might be hundreds of miles away, in the hands of someone who did not understand it. Taking notes was out of the question; parchment was too expensive. Restrictions on travel and communication due to a plague amounted to minor complications.
Well, the tension was finally resolved when “saving the phenomena” became the criterion for scientific truth. To modern scientists, the Medieval tension between astronomers and philosophers seems kind of quaint, something we’ve long gotten past. And yet, we’re not so sure. In active science we still see the arguments between those who emphasize the coherence of theory and those who emphasize discrepant data. Such arguments mostly get resolved, eventually, with more and better data. But maybe it’s a good tension to have in the process.
