theleveller wrote:

"...an artificial construct backed up by a spurious and arbitrary definition - Seems more likely that there have always been popular songs which are relevant to a particular time and context."

The second bit is partly true, but not the whole story. Roy Palmer's great book 'Working Songs' uses historical accounts to demonstrate that industrial protest songs were actually sung widely (including in pubs) during the period of their composition - which was welcome because previously all we had to go on were a host of printed broadsides and the occasionally suspect claims of Bert Lloyd - but we still don't have evidence that those songs were passed down through succeeding generations.

The kind of songs that folk revivalists have generally concentrated on are a bit different, though. These were songs - many of which actually were the popular songs of the 18th century or before - that took such a hold on the populace that they were still being used for diversion, public and private, two hundred years later. People in East Anglian pubs were still singing songs of the Napoleonic wars, or even older and more mysterious pieces of magic and terror, as late as the 1950s, when by which time any relevance to the singers' pesonal experience was long gone.

To make a similar claim for 'Johnny B. Goode', you'd have to imagine a future counterpart of Cecil Sharp or Jim Carroll finding people who not only remembered the song but could sing all of its verses (and remember those 18th century songs had many more verses) without any kind of prompt, in 2158. And for that to have happened in a world without sound recordings. And for all of those singers to be using subtly (or even wildly) different versions of the words and tune.

Blandiver wrote:
"I'm using Folk to mean The Revival. I think it's not unreasonable to see it as unbroken continuum from the early years of the 20th century to the present day."

In that case you seem - in comments such as "it seems to be the aim of Folk to filter out what it sees as the 'pure stuff'" - to be assuming that there's been no evolution in thinking over a period of 100 years: between Sharp and his followers on the one hand, and A. L. Lloyd, Steve Roud, Georgina Boyes on the other. Rather difficult to sustain!