Greg asked:

Philosophy is about investigation our world and seeking answers to certain of life's questions. In fact
there is a philosophy fo just about everything (philosophy of science, of religion, of language, etc). But
all of these disciplines and areas of study have certain things in common that make them all part of
Philosophy. What do all areas of Philosophy have in common? What makes a question a
philosophical one? What is the common thread that connects these?

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Well, this is a deep question in itself, and I don't think I can cover it all here. However, I will offer one
observation (with acknowledgement to Laurance Splitter, from whom I have pinched the idea).

All disciplines share one thing in common: they use concepts. Concepts are the life blood of thought,
and hence of the disciplines. Philosophy explores concepts, and helps us to use them well. The
concepts that philosophy is best equipped to explore have three features: they are common (they
come up all the time — people use them a lot), they are central (they are very important in making
sense of things) and they are contestable (while everyone uses them, when you look closely at what
they mean, it is difficult to pin them down exactly — different views of exactly what they mean can be
advanced, and each of them seems to have its strengths and its weaknesses).

The concepts across disciplines are not always the same, though there is some overlap. When there
is overlap, it isn't always clear that the same concepts work in the same way in each discipline. A few
examples of some concepts from the disciplines you mention. Science: proof, evidence, explanation,
beauty. Religion: God, proof, evidence, symbol, faith. Language: meaning, symbol, intention,
explanation.

Tim Sprod