I've been doing a lot of research on early astronomy lately and have been digging into how exactly we know what we know about the early Greek astronomers like Thales and Anaximander [1]. It turns out that it's pretty remarkable that we know anything whatsoever about these early figures.
Thales was active so early on that philosophers weren't really writing anything down at that point. One of his successors, Anaximander, wrote his ideas down, but did so in verse rather than in prose, and even still, those works were lost to history. But centuries later, a student of Aristotle named Theophrastus wrote a text called History of Physics (or something similar), which was by all accounts a thorough exposition of the thought of the major Greek natural philosophers up until his day. But this work was also lost.
Fortunately, however, a later author, St. Hippolytus, wrote another work called the Refutation of All Heresies, which used Theophrastus's text as a source and basically went point by point through the various philosophers that Theophrastus covered to explain why each was wrong. St. Hippolytus was so thorough that we can actually reconstruct the original chapters in Theophratus's work. So one of our main sources for the ideas of Thales and Anaximander comes to us two sources removed from the original.
There are other sources for the ideas of Thales and Anaximander, but it's a similar story where the surviving works have been filtered through sometimes as many as three intermediate works that were all lost. So understanding the ideas of these early astronomers means piecing together fragments from a lot of later works, trying to figure out the chains of transmission and the potential biases at each link. It's almost as though we were living 2000 years in the future and trying to understand the ideas of Charles Darwin, but the only sources we had to go on were a newspaper clipping from the Scopes Monkey Trial and a Reader's Digest version of a book by Stephen Jay Gould. Understandably, the error bars on our knowledge are pretty big and there's very little we can say for certain.
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