I have been reading Fowler's literary history of the ballad, and finding it reasonable. His basic approach is to take the earliest written examples of 'ballads' he can find and to try to trace changes in form/structure through the ages.

If I have read him aright, he believes that the ballad as a literary form arose out of a mixture of the romances and 'vernacular' literature including old carols, all of which he discusses via written forms. Some of his history struck me as a bit too broad brush. But he was a person with a very wide knowledge of old materials and texts.

I am thinking that this book will have particularly interested a person who wanted to look at dating particular songs?

I suppose Fowler is a 'mediator', he takes material and analyses and discusses it in terms of his own values, which would include a view that the ballad is a 'literary form' and that it makes sense and is important and interesting to trace how certain features of it developed.

Probably worth a thread on his own account. Thanks for the reference.