The vigour of some of the posts above should make me hesitate but I have a small experience that exemplifies some of the notions about keys, modes and scales, as presented in the various posts.

I was never able to read music but I knocked around with people who could. Some were into singing unaccompanied (by instruments, that is) harmonies and some of us formed a group that was well thought of in such activities. The discussions about resolved and unresolved chords etc enabled me to learn, informally, a fair amount of music theory. I suspect many on Mudcat would have had similar experiences.

After years of unsuccessfully trying to find an instrument I could get to grips with I was staying with a mate (Mike, with whom I sang and who could play mouthorgan pretty well and who was getting on top of 2- and 3-row button accordions) just after he had found a gaudy (Italian white laminex) 20 button C/G anglo concertina in a remote secondhand shop. I picked it up and discovered I could knock out a tune on it. He encouraged me with the comment that it's methodology was similar to a single row melodeon that I'd been given but could never work out how to play; I was away!

Not long after this I acquired a Lachenal 20 button, also in C/G. I sat in on sessions and soaked up tunes like a sponge, having a go at everything and anything; I rapidly learned I could find the notes for some tunes but not for others and this was determined by the "key" of the tune. I couldn't yet tell by ear, which I could attempt with probability of success and which I couldn't but, with Tony playing his A/D/G button accordion in the sessions, I recognised that I could usually play (or learn) tunes that he played on the inside (the "G") row of buttons.

At one session in Canberra, in the middle of a bracket, the tune changed to one I thought I recognised as one I could have a go at, but I couldn't see which row Tony was using. I leaned past Kate, a fiddler of serious mein and vast experience and competence and saw Tony's fingers on the G row of buttons.

"Ah, G!" I muttered.
"A minor!" retorted Kate, without hesitation or dropping a decoration.
But I could play it on my G row and did so.

Now, I knew enough of Imogen Holst's book on music theory to understand that you needed particular notes to ascend a minor scale and other, different ones to descend it. And I knew that the single row melodeon didn't offer such differences in notes but you could still play 'minor' tunes on it. I was stumped.

Until I met Karen, a classical violinist with Conservatorium theory under her belt and who was also into playing traditional fiddle tunes. Karen explained the differences between "keys" as most practitioners of western art music since Bach use the term, "modes" as ethnomusicologists use the term and "scales" as hoi polloi like me use the term. And many of us use them interchangeably, sometimes with great clarity and sometimes with confusion.

The heavies on this thread will probably wince at my attempt to give a simple explanation but faint heart ne'er won fair maid, so here goes.

Before Bach's "Well Tempered Klavier" (probably better interpreted as "Even Tempered Klavier") there was a plethora of scales, usually referred to by us as keys. Many were modal, in that they had the sharpened fourths and flattened sevenths etc etc that enabled them to be classified and named differently. Competent players of fretless fingerboard instruments (eg violins) or ones with moveable frets (eg lutes) could easily play all of these without much trouble. Players of small instruments using fixed pitches (eg winds) could carry several and just swap them as required. Players of keyboard instruments (eg clavichords, organs and pianos) had major problems; if the instrument was tuned correctly in C (and I'll avoid using the term "key" but you'll all know what I mean) the tuning would be perfect for tunes in C, passably acceptable for tunes with one or even two sharps or flats in the signature and progressively worse as there were more sharps or flats. Back fixed all this by making all the notes between octaves equally (or "evenly") "off" the correct note. He then wrote his 48 pieces in every "key" in the western tradition and played them all on the one instrument without retuning between pieces.

At a stroke, he'd solved one problem but introduced the confusion about terminology. While we (with our ears tuned to Bach's mean tempered tuning, now universal in most westerners' experiences of classical and pop music) may talk about playing all the white key notes on a piano from C to C as illustrating the Ionian mode and the white notes from D to D as illustrating the Dorian mode, the heavies among us will know that the actual pitch of the starting note for the Dorian scale is not any D on the piano but a different pitch entirely. Further, the intervals in the Dorian scale (in tuning proper to the Dorian mode) can't be reproduced on a piano unless we completely retune it; it will sound sweeter but be unable to accompany anyting except instruments (eg voice, violin, retuned fixed-pitch instruments) with the same tuning.

So, the posters who write about usage all have a point and are correct but its wretchedly confusing for most of us until we get the hang of what's going on.

In a spirit of helpfulness, hopefully.

Cheers, Rowan