This is like trying to nail Jell-O to the wall.

By now I know better than to try to make any assertions on this matter without first putting on my Kevlar vest. So I'll just make a couple of observations and raise a question for your consideration:—

Observation #1.
As far as anyone knows, the first person to use the term "folk song" was German philosopher Johann Gottfried Von Herder (1744-1803). He felt that the only way to escape from what he considered to be a contrived, artificial, and gutless Kultur was to delve into the spontaneous culture of Das Volk. A study of volkslieder, for example, would give a more genuine picture or what a county's culture could be and should be. It would give it it's own distinctive character, rather than an artificially constructed one. Volkslieder = folk song. Songs sung by the rural, peasant class. He and a few others sparked an interest in preserving this material. The rest is history.

Flash forward a couple of centuries. In this modern world in which we give lip-service to being a classless society, we don't like to think of things such as a "rural peasant" class (further refusing to acknowledge the possible existence of an urban peasant class). So the term volk, or folk has changed its meaning. Now we are all "just folks." If a definition is all-inclusive, by the definition of definition, it ceases to be a definition. (Got that?) Therefore, the words "folk," and, hence, "folk song" the way they are currently used, are essentially meaningless.

Observation #2.
It seems to be an article of faith among singers of folk songs such as ourselves that the "Folk Process" invariably improves songs, polishing off the rough edges with time and usage and gradually converting a more or less indifferent song into a finely honed work of art. Not necessarily. Sometimes a song degenerates badly as a result of the folk process. By way of example, look at the text and music of The Three Ravens (Child 26) pretty much as it appears in its earliest source, Melismata. Musicall Phansies Fitting the Court, Cittie, and Countrey Humours by Thomas Ravenscroft (1611). Then take a look at this later version. Or this.

I rest my case.

Question for your consideration:
Who defines what folk music is, anyway? Anthropologists, ethnomusicologists, and folklorists? Or we "folk singers," most of whom have read a bit, but have done little actual scholarly work in the field, and who have learned most of the songs we sing from songbooks, records, and CDs? If this is ever to be pinned down, it will take some considerably more rigorous thinking than the usual "horse" or "folk songs are songs sung by folks." That's just bloody lazy.

Although I use the term "folk singer" in reference to myself, I don't really regard myself as a folk singer. I am a singer-guitarist. I sing a lot of different songs: the vast majority of them happen to be folk songs.

Don Firth