I've always found it a bit of a confusing distinction, and can't really see that a "source" singer is anything of the sort: the source of traditional songs and music goes back a lot further than the so-called "source" or "traditional" singers.

It's not about oral versus written tradition. Many of the traditional singers and musicians performed songs and tunes that had at some time been written down, and they may or may not have learnt them from written words or music. Equally, many "revival" singers(and many reading this, I should think) have learnt many songs and tunes from others without ever seeing them written down.

And it's not to do with occupation, either. Even the singers who are accepted as "traditional" used to sing songs that did not arise directly from their experience - they may have sung seafaring ballads and yet never seen the sea. It would be a dull old world if farmers could only ever sing songs about sheep and lbrarians about books.

The "revivalist" folk musicians and singers who are now the custodians of traditional music are teachers, computer operators, engineers, salesmen, etc, and not sons of the soil, but they still share and pass on this music. They use modern methods to do it, but this doesn't invalidate it in any way, IMO.

Musically, we've always been open to other cultural influences. Polkas and waltzes came from central Europe, jigs probably from France, and so on. So it's not a matter of cultural purity or intergrity, either.

So the more I think about it, the harder I find it to recognise any real distinction between traditional and revivalist musicians and singers. There's a much bigger distinction to be drawn between, on one hand, all those who respect and are inspired by traditional sources, and on the other, those who concentrate on recently-written material that has little to do with the tradition. But that is a whole nother topic....