Without making any attempt to define "folk" (God help us) I'll pass this thought along. I once taped some lovely songs from a lady. Now the lady was a professional singer and was somewhat successful in the small pond of Scots television. Thing is, I was taping her at home in a tiny Outer Hebridean village. She was also a source singer.

She strongly felt and expressed that I really wouldn't want to tape her because at home, she could only bring herself to sing "home style." She was sure I wouldn't enjoy that and that I would be disappointed in not hearing her "stage style." It took a good bit to convince her that home style was exactly what I was hoping for and most wanted.

Well, she sang some of the loviest songs I'd ever heard including a Gaelic spinning song I've nevder come across elsehere. It was the home style that gave her singing all the warmth and "reality" that was missing from her professional style.

I suggest that this is something of what Heaney meant. One is a family song offered to be shared with listeners interactively - the other a Performance of a professional from a raised, separated platform. One-way. But there it is, from the same singer & even maybe the same song- but one is "folk" and the other is "commercial."

That's what I think.