Are you defining music regarding its source or its style? Songs of an impeccably 1954 folk origin may cease to be folk (for me) when sung by a classical tenor with piano accompaniment, or by a rock band with electric guitars. A song whose origin doesn't meet the 1954 definition but is sung in a more 'traditional' style, may be more acceptable (to me) as 'folk' by a stylistic definition.

Definitions are tools, and you use different tools for different jobs (at least, most of us do). One definition may be a tool to define the field of study for academic research into texts and melody lines, and concentrates on the origins of the material, another may be more concerned with what the performance sounds like.

I like (but don't claim as my own) the definition that 'if you can't carry all your gear from the car to the venue in just one trip, it's not folk music'. One thing I don't do, is claim that my definition has to be, or should be, accepted by anyone else. I really don't care that much.

Andrew