Very good point. In general, the way I understand it is that most of what the ancients believed about the universe was based on empirical observations. They di

Very good point. In general, the way I understand it is that most of what the ancients believed about the universe was based on empirical observations. They didn't just come up with some arbitrary theory, they had observations and they were trying to explain them. The epicyclical model persisted all the way to Copernicus (whose model also had epicycles) just because it was so good at predicting future observations. I think their main axiomatic assumption that was based on their metaphysical beliefs, rather than actual observations, was the assumption that the luminaries must move on circular orbits. Again, to my understanding, they had a mechanistic view of the universe that demanded order and symmetry, and they just couldn't imagine how a planet would move in any other orbit than a circle- hence why they were mystified by the apparent "retrograde" motion of the planets and had to come up with epicycles to model it. The combination of their axiomatic belief in a mechanistic universe and the limited observations they could make with the naked eye conspired to keep them from a better model.