Who are we Pagans? And how can we tell?

As modern Pagan religion has grown and flourished people increasingly enter it from different backgrounds, and once involved, explore in different spiritual directions.  Is there a common core?  I argue yes, and it is an important one.  As I work out the implications of this claim a small book is likely to be the result.  But the core of it will appear in a series of essays on the interfaith blog Patheos.  Here is part I.