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According to Wikipedia, there is no account of how the sphericity of the Earth was established. Though it goes on to say 'A plausible explanation is that it was "the experience of travellers that suggested such an explanation for the variation in the observable altitude and the change in the area of circumpolar stars, a change that was quite drastic between Greek settlements" around the eastern Mediterranean Sea, particularly those between the Nile Delta and the Crimea'

According to the same article the Sphericity of the Earth was widely accepted by the Greeks 5th century BCE. With Aristotle providing, what appears to me fairly flimsy arguments in 4th Century BCE, and more compelling evidence by Aristarchus in the 3rd BCE. This is quite a time-lapse, and hints at Aristarchus providing evidence for a theory already established. (A contemporary analogy would be Eddingtons expedition providing evidence for Einsteins theory of Gravitation - whose compelling physical idea was the equivalence of inertial & gravitational mass)

As the Greeks moved from a mytho-poetic cosmology to one focused on rational enquiry, were there general philosophical ideas that arose, and that would have proposed and made convincing the case for a spherical Earth?

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    The title of this question looks to be a historical one, better asked on History. The body of this question looks like an answer to another question, or perhaps a blog post. That is to say, you appear to be making an argument, rather than asking a question. If this not a purely historical question (as your title might suggest), then please consider editing to make more explicit what your specific philosophical question is. Often times, good questions will end with a summary of what is being asked. – Cody Gray Apr 20 '12 at 2:28
  • ok, I'll think about it. – Mozibur Ullah Apr 20 '12 at 2:34
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    "philosophical ideas"? I don't think any philosophers determined the Earth was spherical purely through a priori reasoning.... if you mean "scientific ideas" (a posteriori) then this is probably better fit for history, as that would cover history of science. – stoicfury Apr 20 '12 at 19:43
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As the Greeks moved from a mytho-poetic cosmology to one focused on rational enquiry, were there general philosophical ideas that arose, and that would have proposed and made convincing the case for a spherical Earth?

Yes: observation. The sight of ships appearing on the horizon (masts first) makes the curvature of the earth evident. I think a better question would be why any culture situated adjacent to an ocean or a sea of sufficient size would ever believe the earth to be anything but curved. Furthermore, as you point out, for a sea-faring people (or a widely travelling land-based people), the celestial evidence is highly suggestive.

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    "observation philosophy" = looking at curves and not calling them flat? XD – stoicfury Apr 20 '12 at 19:46
  • I don't find that convincing enough. Couldn't you just have a curved flat Earth? After all the Earth itself is not perfectly flat. Other cosmological systems had a bowl, why not an inverted bowl? – Mozibur Ullah Apr 22 '12 at 5:46
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    Some systems did have an inverted bowl. In the absence of evidence to sway things one way or the other, I suppose it came down to which explanation seemed more fitting. The point being, as they moved to a cosmology focused on rational enquiry, they adapted the cosmology to fit with their observations. – Michael Dorfman Apr 22 '12 at 9:53
  • @dorfman: I know Aristotle made the same argument you stated, but I'm sceptical of the sail of a boat appearing first on the horizon. Imagine a boat with a square sail, say 20 metres high, with a hull say of 2 metres showing above the sea, how reliable is an observation going to be when said boat is 2 km away. The boat would appear to the eye as a cm in height. The kind of arguments I was thinking of are: – Mozibur Ullah Apr 24 '12 at 16:56
  • 1. is the earth limitless in extent? Suppose not, then it must end in all directions, including beneath us. In which case we have the earth hanging in space. – Mozibur Ullah Apr 24 '12 at 16:56

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