Quite a few exceptions!

Only if you accept spontaneous variation as improvisation. Many singers, traditional & otherwise, never sing/sang the same song the same way twice - and random factors abound in sessions and singarounds which always make you think about a song differently to how you might have thought about it last time you sang it. To what extent did such factors effect The Folk Process? which many see in terms of it being purely random (mondegreens, Chinese Whispers, memory loss etc.) rather that the consequence of deliberate changes made to a song by a particular singer by way of making it their own either as something they purposefully rehearsed to do, or else free-styled in a given performance.

Whilst such things intrigue, folk hasn't given us anything in which improvisation is the determining factor of the music, or yet absorbed the aesthetics of noise, atonality, dissonance etc. in the same way rock & jazz have. Whilst certain early musicians have explored these sonic possibilities, and saving Felix Doran's farmyard sounds in his rendering of The Fox Hunt, what you hear in folk is determined by an abiding obediance to a fundamental harmonic orthodoxy. However so stridently spontaneous this can be at times (see previous post), I think I might have difficulty in accepting such as improvisation in the purest sense (though there are times...) much in the same way many here might have difficulty in accepting Derek Bailey's playing as being in any way traditional, which I do, of course.

Maybe at the sesh tonight I'll just start improvising and see what happens, sure as hell my partners in crime would go for it after a pint or three... Watch this space!