Jack - you seem to have a wider and more deep Musical Education than I - I am just a 'generalist'.

"The point is, what do you want the modal system *for*?"

Ah! :-) Everybody wants it, like some 'token of the true cross' to prove that they are much better than others... :-)
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"saying melodeon players simply shouldn't play tunes in modes where the fifth from the tonic isn't a pure 3:2?"

You used that WORD again - which has so many confusing differing meanings... :-)

No, I am not saying that - but the Word 'Mode' in Music Theory/History has some very restricted meanings - and I use the plural advisedly - if you have been following this torrent of words, you SHOULD understand why, cause it meant apparently different things to people in different periods of history!!!

OK, I'll agree that these players may be trying to IMITATE something like that!!! But melodeon players (or any other Musician who wants to be taken seriously) 'playing instruments where the fifth from the tonic isn't a pure 3:2' should not attempt to delude us, or themselves that they are doing something seriously 'OLD' and - Shut your eyes!!! 'TRADITIONAL'!!!! by pretending to play in Modes!!!..... If they DO insist on trying that on, some people may well chuckle and mutter the naughty 'W' word under our breaths!
:-)

The trouble is that IF we insist on degrading the words used to describe precise things, then the words end up having no real meaning! Which is what Lewis Carrol was satirising with the Humpty Dumpty quote I used above.

Take for example the current argument about wanting "Intelligent Design" to be taught in "Science" Classes. "ID" can NEVER be part of Science(@@@), as it is a 'Belief System'! I don't wish to STOP teaching of ID in schools, but please put it in the correct place, in the 'Philosophy' subject - the Study of 'Belief Systems'. WHAT? You don't want 'Philosophy' taught as a real subject cause there are too many 'subversive ideas'? Subversive to what? YOUR Absolutist 'Belief System' (Narrow minded Religion)???
:-)

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(@@@)
Oh, all right! 'Science' IS a 'Belief System' ;-) but founded on certain very strict Rules which involve 'ONLY objectively examining the (physical) evidence before us'. All 'Religions' are 'Belief Systems' too, but they are based on the exact antithetical 'Basic Belief System' - they DO NOT QUESTION, but only BLINDLY ACCEPT (you are with me or against me!) the given thesis AS A MATTER OF FAITH! Pity that some cults of Politics (also based on systems of Beliefs!) are trying that path now...

OK, so I can get very pedantic...

But if you want to play 'Modal', just exactly what sort of music do you want to DO? If you have only the vaguest of inexplicable ideas (in terms that others UNDERSTAND using words with already well established meanings, that you think just sound 'trendy') about that...
Nothing wrong with Music that sounds vaguely 'Sorta-Mode-Like', really... :-)
Just don't try to pretend that you are upholding some 'Ancient Music Tradition' that way...

Now... Anybody want a serious discussion on 'What is Folk Music?'

:-)

Robin