What counts as philosophy: my point wasn't that science should be included under the heading of "philosophy", but that scientific advances may have had a big impact on philosophical questions.
Morality: I think I wasn't clear enough. (Either that or I'm now misunderstanding you.) I wasn't saying there might be no fact of the matter about whether moral realism is correct; I was saying that if moral realism is incorrect, there might be no fact of the matter about any question of the form "is doing X in situation Y morally right or not?". (As to the question of whether moral realism is incorrect, I am inclined to agree with you that it is. But that wasn't my point; I was just offering a concrete example.)
On that matter, could you give some more evidence to demonstrate your points? I'm curious but a bit skeptical without examples to back it up- modern philosophy is in a metaphorical sense designed by retreating further and further from empirical questions, and thus would not have in its domain questions which scientific advances can help with.
As for morality- let's assume moral realism is incorrect (a highly credible hypothesis). This puts moral realism on the same sort of level as free will. Therefore, if asking "Is doing X in situation Y morally righ...
Since LessWrong is a major congregation point for certain philosophical ideas, and because people here tend to be more objective (in the sense of not being self-deluded) than elsewhere, I thought I'd ask people's views.
To be clear, by "Greatest Philosopher" I am referring not to the most correct philosopher in human history but the one who deserves the most credit for advancing human philosophy towards being more true.
Off the top of my head I would say that a prime candidate would be Hume- amongst other things he rejected the idea of a soul, realised to a much greater extent than his predecessors the limits of human knowledge, and opposed the idea that reason is somehow an objective force that can make priorities independent of emotions.
Aristotle deserves considerable credit relative for his time but doesn't make the list because although it wasn't his fault his ideas were dogmatically accepted and held back both science and philosophy later on.
Your thoughts?