"What exactly is a pagan? I'm not trying to be flip, but how would I distinguish a pagan from an atheist?"
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Well, pagans make an attempt to adhere to a belief system that is based on old, pre-christian european spirituality. The drawback is most of that information was probaly lost so, without being disrespectful to them, I have to say that they are basically 'winging it'.
Why, IT is a nagap spelled backwards of course.
That is a$$ backwards in every respect.