Ok, this most might be a bit long, but I wanna make sure you're not leaving this feeling more confused or more lost than ever with modes. So I might repeat myself a bit in what I'm writing and ramble a little, but I'm just trying to drive it all home.grooki wrote:
OK I think get it now, that makes a lot of sense. But from what you were saying in the first post, these modes can somehow be used while playing in another key and scale? Is it that when you have a chord progression, if you use whatever the current chord is as the root note to an accompanying melody, those melodies will be in whatever mode is designated by the degree of the chord?
I think maybe the two examples I gave are what's causing the confusion? Forgive me if I'm wrong here.
The first example was this
Chords used: C Major for 2 bars || F Major for 2 bars || G Major for 2 bars || F Major for 2 bars ||
Modes used: C Ionian---------------|| F Lydian---------------|| G Mixolydian---------|| F Lydian -------------||
The whole way through this, we're still in the key of C Major, and even when using F Lydian (because F Lydian has all the same notes in it as the C Major scale has)
The second example I gave was this:
Chords used: C Major for 2 bars || F Major for 2 bars || G Major for 2 bars || F Major for 2 bars ||
Modes used: C Major scale--------|| F Major scale-------|| G Major scale--------|| F Major scale------||
And what I was trying to say was that doing it this way, i.e., using the F Major scale under the F Major chord, while it seems logical, isn't. As it would denote a key change. Because the C major scale contains C-D-E-F-G-A-B-C and the F Major scale contains F-G-A-Bb-C-D-E-F and the Bb you find in the F Major scale isn't found in C Major, so playing it over the F Major chord (as part of your F Major scale) would give a sense that we've changed key, rather than just moved to another chord within C Major. It would seem like we've gone from the key of C Major to the key of F Major. The same problem occurs when we move from F Major to G Major, and play the F Major and G Major scales under them. It denotes a key change again. Which is problematic.
Which is why we use the modes. F lydian contains all the same notes as C Major, and G Mixolydian contains all the same notes as C Major (they just start and end at different points) so when we use F lydian (rather than F Major) we're still displaying that we're in the key of C Major.
The stuff on modal interchanges and pitch axis theory do involve key changes, but you'll never get a key change from say C ionian to C locrian, you can write a musical theme and have say 6 bars where you've written using the notes of C ionian, then for the final two you can have two bars using the notes that would denote your using C locrian - now, that isn't a key change from C ionian to C locrian, what that would actually be would be a key change from C Major (because C Ionian is the mode extracted from the first degree of C Major's scale) to C# Major (because the locrian is the mode we get from the 7th degree of the C# Major scale and that's how we know C locrian is in C# Major) but if you were describing it you might say that the first 6 bars felt like they were ionian and the final two felt locrian.
Hopefully that helps clear up the whole 'key change' business for you.
It is a hard concept to get your head around at first, people rarely get modes and their uses first time around. For most people, it's one of those things that you sit down to try to learn, get confused, and forget about, and then you repeat that process for months, sometimes years, and eventually one day it just clicks. The best way to deal with them is to take it in tiny chunks, don't try to digest the entire of the first post in one go, take it in little steps and make sure you're confident with each small part before trying to digest it all. And of course if you've any more questions, or if something I've said seems a little foggy or difficult to understand, just ask and I'll try my best to clear it up.
And I recommend searching around on the net for other videos or written lessons about modes because sometimes hearing the same information from different sources and in different ways helps you understand it a little better.
EDIT ii: Sometimes people who are a bit more used to using modes will start speaking in a sort of 'shorthand' so they might hear a steve vai tune like km-pee-du-wee and say "that's in E lydian" this is kind of a short hand way of saying "that's in B Major, and he's using the 4th degree of the scale, which would be E lydian" we're not actually saying that the key signature of the piece is E lydian, we're just kinda saving ourselves a massive mouthful.
How did you get banned from FOTB? It's way to easy to get banned from that forum anyway. I have been banned 3 times and I'm far from being a tnuc. 
bigup Kaiori 
