This thread didn't go the way I was expecting from the title. If I may explain?

You sometimes hear an artist say "I was given this song by X". Now does this mean that the artist was playing with X one night and X taught him the tune? Does it mean that it was one of X's compositions, and the artist no longer needs to pay copyright fees when he plays it? I suspect not. Surely it means more than "I heard this song on X's CD and learnt it from there."

So just what does it mean?

Regarding the main direction of the thread: I don't sing, but my wife does. She learns songs from CDs, or in singing workshops, or sometimes asks help from other singers. If we all followed this "You can't sing this song it is mine" there would be no folk singing at all, songs would never be passed on and never heard away from their place of origin. The whole concept seems to be alien to the folk movement. Indeed, it seems to be alien to any kind of music practice at all.