Yeah it could be looked at that way, but it's a very simple way and ultimately it does limit the understanding of harmony. Outside of writing a chord progression in a mode which I understand your trying to say aiwass.

Modes are used to explain the harmonic sound of playing a major scale over all the chords that exist in that major key (modernly speaking). Say your playing a C major scale over a F major chord, well that will produce one harmonic sound (lydian). Play the same scale over a C major chord and that will produce a different harmonic sound (ionian). What your trying to understand is the harmonic quality you get from using a certain mode. The greater understanding is distinguishing the harmonic sound of modes so you can freely utilize them later. Once this understanding is made sense, modes aren't just a branch off a major scale. As I wrote in the example before, you can see how it broadens your musical sight past just major and minor scales. It’s a slightly more advanced study of music, but once you learn to use them this way; they become an iatrical part in music paralysis. I’m just trying to get you to understand modes before you knock them, that’s all. They may help and they may not.

As for songs written in a key like C major, writing in the F lydian mode is very rare because the key signature ultimately reflects the last chord in the song. If you write a song in the key of C major, 95% of the time that song ends with a C major chord. So if a part of the song or all of the song is in F lydian, the key signature is easily written as F major. Even the F in F lydian is a major chord, it wouldn‘t be correctly written if it was C major.

Exceptions are modulation. Then the new key signature will end on that tonic chord. The other is like you say “modal“, but those songs will end unfinished. The F major chord is going to want to resolve back to the C major, if the key is C major. Choosing not to do that is an effect, and that’s all. What is the difference as your probably asking. Well it’s probably the first chord played or dominant chord in the song. Which when you write in a key signature, the first chord is either the V(v) chord or the I(i) chord. So in the key of C major that would be either F major or G dominant, in the key of F major (lydian); the difference would be either F major or C major. There is no dominant chord if the lydian scale is used. The natural dominant is G, which is the II7 chord in the lydian mode. Hopefully you see now.

[Edited by noticingthemistake on 04-11-2003 at 12:08 PM]