I thought I had learned something from that recent thread. So, last night, I decided to make some two-octave-plus-9th scales, ascending and descending, for practice. I got out the staff paper and started with Bass Clef, C Major, so the first note, C2, went in the second space and I trailed dots off to the north-east from there. But when I got to D4, I thought, "Wouldn't it be good to go all the way up to the top range of my instrument?" So I did--up to F4, for my instrument. Then I ran dots back down toward the south-east to C2. Then I thought I'd keep on going to the bottom of my instrument's range, too, so I did--down to E1. Then I went back to the front and added scale notes from E1 on up to the first C1 that I originally had started with. So now I had a chart of the C Major Ionian mode for the full range of my instrument. It didn't start on C, but so what? If I wanted to practice it by starting on C, I could. Okay, so then I decided to do the same with the second C Major mode: D Dorian Minor. This time I just started on E1 and ran the dots all the way up to F4 and back down to E1 again. Well, I don't think I have to tell you what I ended up with: My C Major Ionian and D Dorian Minor charts were identical. All because I included the full range of my instrument on both of them. (Talk about feeling like a fool. I knew all along that D Dorian was, by definition, the C Major scale starting on D, but . . . . somehow it didn't register until put it in print.) So, now I'm thinking: Suppose I play regular C Trombone instead of bass. (I want to eliminate the play-the-root obligation thing.) And let's say I'm going to solo for eight bars that have nothing on them but the chord symbol Dmi7. Okay, I know that an experienced jazz musician, like many of you guys, could do a lot of different things here, if he wanted. But one of the things our not-so-experienced trombonist could choose is simply to improvise in D Dorian Minor for 8 bars, correct? Well, what if he chose simply to improvise in C Major Ionian for 8 bars instead? Would there be any difference? There can't be a rule that says if you're going to solo in D Dorian Minor, you must begin on a D--that's so inherently anti-jazz it can't be right. But if you can jump right in on any note in D Dorian or in C Ionian, how are they going to sound any different? If everyone else in the ensemble is thinking and playing D Dorian Minor, and our trombonist is thinking and playing C Major, is there going to be any clash from that? If so, why? That brings me around full circle to the why of the modes, again. The geometry of mode theory is throwing me. I know I am missing some fundamental concept. What is it?