Perhaps a little bit of a strange topic as, common sensically, one can be all three. 

(I'm new to the forums and I don't know whether RDF.net is the appropriate place to call for a philosophical discussion on Atheism?)

As far as Atheism is concerned I'd really like to address those 'positive' Atheists who see Atheism as having some definite - if unclear - ethos and/or social programme.  (I consider 'negative' Atheists - agnostics or de facto Atheists -  to be happy-go-lucky instead of just lucky, and so excessive in some respect).  The social programme is typically Humanism, which is thought to have intellectual space thanks to the great success (isn't it!) of Darwin's theory of evolution by natural selection.  I am completely convinced that evolution by natural selection really does put the scientific torch to religious thinking, so kudos to humanity on that front.  The thing that makes me want to ask people more questions is this apparently blind acceptance of Humanism as naturally following on from the science.  Part of me wants to think that this is just because, ethically and politically, Humanism (especially through Human Rights Law) is the only game in town.  I have noticed, however, that the three terms Atheism, Naturalim, Humanism are used pretty interchangeably and I worry that Atheists are in fact conflating them while there are important differences that could be helpful.

As I don't want to be too academic about it