background: I'm an amateur and self-learner pianist. What I know, I know from books or google, so I'll start with summarising what I already know - please don't hesitate to correct me if I have something wrong here.
I know that in western music there are different "modes" (= kinds of diatonic scales?). All that modes have a lot in common: they build the whole octave from intervals of 5 full tones and 2 semitones in some order. Various permutations of those intervals yield different modes, and the only constraint is that the two semitones must have 2 or 3 full tones between them.
Different such permutations (= different modes, = different kinds diatonic scales, synonymous?) have different Greek names:
T-s-T-T-T-s-T = Dorian mode,
T-T-s-T-T-s-T = Myxolydian mode, etc, etc. Cool.
- Ionian mode,
T-T-s-T-T-T-s, is also called "Major diatonic scale",
- Aeolian mode,
T-s-T-T-s-T-T, is also called "Minor diatonic scale".
Almost all songs I encouter are written around either of the above scales (in an arbitrary key). Why those two (and only those two, I suppose) got their own "mainstream" names and are used much more commonly than the remaining possibilities, and the rest are somehow "in the shadows"? I'm used to names such as "Toccata and Fugue in D minor", but I've never heard anyone entitling a piece "Waltz in C Dorian", for instance. Do composers avoid those scales or something? Doesn't the variety allow for more expresiveness? Is there any practical or historical reason for that phenomenon?