Phil, one of the joys of the English language is the number of words that can have the same meaning. Actually, I think the phrase used initially was in the folk 'idiom', but in the context of this debate, 'form', 'style' and 'idiom' all have exactly the same meaning. Although of course, Mr Carroll did tell us that folk is not a 'style'

The problem, that I think you've missed, is that Mr Carroll has declared that we can 'qualify' traditional song that fits 1954 with the word 'folk', but has also complained that he does not know what to expect if he turns up to a 'folk' club. So, following his logic, we need to 'qualify' other songs with something. Now you would not call an opera piece just a 'song' so in order that Mr Carroll knows what he's going to get when he visits a 'folk' club, we need to qualify those new songs.

What I've been asking, but he has declined to answer, is HOW do we qualify those new songs that are in the style/form/idiom?

Me, I just call them Folk!