I think we are confusing a number of issues, here.

A singer is, more often than not, labeled by the kind of songs that he or she sings. If a person sings traditional songs, people will call him a "traditional singer"—even if he was born in a big city and his father and mother were well-paid professionals of some kind. But in most people's minds, since he sings folk songs, people call him a folk singer.

Or a girl who lives in the country whose father is a share-cropper and who goes to a country school is spotted by a sharp-eared teacher as having a particularly nice singing voice. The teacher goes to bat for the girl and she winds up at Juilliard studying voice, and eventually becomes a much-in-demand opera singer.

So the city boy is a folk singer and the country girl is an operatic diva.

Confusin' world, ain't it?

As to amateur, semi-professional and professional, each of the above singers could be any of the three. If they sing simply because they enjoy singing, sing for their friends and family, and don't get paid for it, they're amateur (which is not a judgment on how good they are; some amateurs can be very good indeed!). If they sing for pay every now and then, but don't really depend on it for living expenses, they're semi-professional. And if they derive all of their income from singing, they're professional. Pretty straightforeward, really.

Contrasts:

Jean Ritchie was born and raised in Viper County, Kentucky, and learned her initial songs from family and relatives. A traditional singer, both by what she sings and by birth.   I don't know how much of her income came from her singing, but I tend to think she's professional, or at least semi-professional.

Richard Dyer-Bennet's father was an English peer. He was educated in Canada, Germany, and the United States. He was managed by Sol Hurok, did concert tours and recitals, and many records. He was definitely professional. Because most of the songs he sang were folk songs, most people refer to him as a "folk singer." But HE didn't.

He was a classically trained tenor, a classically trained guitarist, and he considered himself to be, not a "folk singer," but a modern day minstrel, singing a whole range of songs, most of which happened to be folk songs. So--most people call him a "folk singer."

Most of the "folk" or "traditional" singers that I know personally are city-bred and learned their folk songs from song books (Lomax, Sharp, et al) and recordings, or from each other (the others having learned most of their songs from song books and recordings). Most of them sing just for fun, some sing for fun but get paid now and then, and a few earned their living that way, singing in coffee houses, house concerts, and other venues.

One assumes that those who got paid for their singing (semi-professional or professional) were entertaining enough to draw a paying audience.

So it's not real neat and tidy.

Don Firth