An Irish song is one that:
   
   (a) Is written in Ireland, no matter what it is about.
   
   (b) Is written by an 'Irish' person, no matter how many generations removed from Ireland.
   
   (c) Is about Ireland, in even the vaguest fashion.
   
   (d) Sounds as though it MIGHT be about Ireland.
   
   
   Regarding (b) I note mention of Stephen Foster above, and I have seen somewhere that he may
   have had Irish ancestry, therefore his songs must be Irish.