"A folksong in a book is like a picture of a bird in mid-flight printed in a bird book. The bird was moving before the picture was taken, and continued flying afterward. It is valuable for a scientific record to know when and where the picture was taken, but no one is so foolish as to think that the picture is the bird.

Thus also, the folk song in the book was changing for many generations before it was collected, and will keep on changing for many generations more, we trust. It is valuable for a scientific record to know when and where it was collected, but the picture of the song is not the song itself."

Pete Seeger, The Incompleat Folksinger (New York, Simon and Schuster, 1972) p145

Also, how about this:

"...the mass of a people participate in folk song's growth forever reweaving old materials to create new versions, much as an old lady creates a new quilt out of an old by adding, year by year, new scraps and patches. So folk song grows in small steps, with every slight change tested for audience reaction, thereby achieving a permanence in man's affection matched only by the greatest art. This art lives upon the lips of the multitude and is transmitted by the grapevine, surviving sometimes for centuries because it reflects so well the deepest emotional convictions of the common man. This is a truly democratic art, painting a portrait of the people unmatched for honesty and validity in any other record."

Alan Lomax, Folk Song USA (New York, The New American Library, 1947), viii.