I guess it comes down to how you consider definitions to be constructed.
Some wish to define it by 'who' does it. (The famous "horse" metaphor.) Thus, anything done by 'folks' is 'folk'. Cute, but totally useless except as a way to avoid thinking seriously about it.
Others, like Scoville, suggest a narrower, but top-down category such as "origin"....but this could so easily be muddled, as "origin" itself has many categories implied within it. 'Anonymous' origin? 'Age' origin? 'Place' origin? Some combination of those?

   What I prefer is a bottom-up, inductive definition, in which the rules for categories are 'discovered' by analysis OF music which is generally agreed on to be in the scope of the agreed on term.

Example: Take the Digital Tradition database, which is a collection of music submitted and collected by people who have been immersed in 'folk/trad' music for a long time. Now, take all the members of Mudcat and have them examine all the songs in the database, and, to the best of their ability, check off the ones they really think fit.
.....there will be some differences of opinion...Now, make a list of all the songs which are almost universally agreed on to be 'folk/trad'....let us suppose it includes 72.49% of the database contents.

Now comes the fun part.....WHY were those songs agreed on? What are the common characteristics that these songs seem to share that make them so obvious? (and as a secondary project, why were some songs NOT agreed on by a lot of ...ummm..'folks'?)

   I suggest that this would produce a list of from 5-6 to 10-15 characteristics (depending on how thinly we slice) that 'define' the genré. Then, to use the system, we would ask "does song 'X' have some, most or all of these defining characteristics?" This yields catagories like 'age','anonymous author', 'subject matter', 'style', 'commercially directed', 'copywrited' ....etc....

Note..**IT WOULD NOT BE REQUIRED TO HAVE ALL OF THEM**!!!! All this does is to indicate a relative position and help clarify thinking.....and, of course, that is how the DT database was constructed in the first place! Not by formally using this arcane process I have described, but in a subjective way. Since there are no laws to govern this, or official "Board of Musical Supervisors", it would not be written out or chiseled in stone, but if thought about, might cause contemplation....and of course, that is all *I* am trying to do right now....cause any masochists who have read this far to *think* about what categories and definitions are good for and how they are organized.

   Obviously, we are not going to 'have a vote' or 'form a committee' to DO this process, but merely by comtemplating the idea, it is possible to see WHY "Blue Suede Shoes" would get fewer 'votes' than "The Twa Corbies"....and thus, why it makes shopping for CDs easier for people like me if Elvis Presley is not included in a 'folk' catalogue. It is a practical matter! There ARE different 'feels' to various styles of music, and it is flatly useful to have words reserved for them.

I, it happens, am programmed to like older, more 'traditional' music, and, even though I appreciate many of the newer songs, it is usually because they have more of the 'feel' of the older ones. Many of Eric Bogle's, or Utah Phillips' songs have a larger % of the 'folk' characteristics than those of, say, "Nine Inch Nails" *grin*...or even Bob Dylan, though a few of Bob's do well in this subjective system.

Respectively, then, I submit that Trad Jazz, as great as it is, just should not be hit with a label that suggests it ought to be lumped in with Folk...this is just a careless misuse of both language and the reasoning process. For those who might still disagree, I would ask "what purpose does such a label serve"? My idea serves to clarify and make a distinction that is not only needed, but implicitly used every day.