Yes, you are right.

G major would probably work too, if you were feeling adventurous.
Q: Favourite Pink Floyd song?
A: The one where they get wicked high and play Emin and A for an hour.
Quote by travislausch
Yes, you are right.

G major would probably work too, if you were feeling adventurous.

It would work no better than any other scale. The song is in C major so only C major would work. Although the two keys only have a difference of an F or F#, they are still entirely different. To use G major, you would have to transpose the entire song up a fifth.
Quote by Galvanise69
Isnt he theoretically saying you could use C lydian if your feeling adventurous, but you cant use "G" major, even though they contain exactally the same notes, the pull to different places?

Well, he said G major, so he suggested G major and not C Lydian. I don't know the progression off the top of my head, but you wouldn't want to use C Lydian either unless it was defined by the progression; since I don't remember it being a vamp (I could be wrong) you wouldn't be able to stay in C Lydian for long either way.
Quote by Galvanise69
Well ive never seen the vamp, im assuming from you saying "dont use Lydian" it goes over the IV chord.

Which is a perfectly fair reason, sharp root, b2, im assuming its a major chord too, eek..

What I'm saying is that unless you have a one or two chord vamp using chords that are characteristically Lydian (maj7#11, maj13, etc.) then you wouldn't be playing in C Lydian because it hasn't been established.

I have no idea what you meant with that second part there if you want to elaborate, I haven't slept so stuff will likely fly over my head.
Quote by Galvanise69
Well, if there is four chord, a IV chord, and you play a lydian scale based of the root, your sharpening your 1st degree, or putting in a b9/2 to your IV chord.

Which may sound fine on a V chord, but to my knowledge not on a IV chord.

So your saying that unless one of your chords is Maj7#4 (or has a #4 or #11 degree added), it would sound out of place to use lydian?

Yeah, to the best of my limited knowledge your first point makes sense and it would sound off.

And that's basically what I'm saying, because you're looking for notes and intervals that are characteristically Lydian. For example, your maj13 chord must have the #11, because a natural 11 will create tension with the 3rd and won't work, and you'll have strayed from a Lydian feel. The modes are harmonically unstable, so if you stay within a couple of chords (maj7#11, maj13, add9#11 and so on) you'll be okay. If you stray from characteristically Lydian chords then the progression will want to pull somewhere else.

Does that clear anything up?
Quote by Galvanise69
Yeah, that makes sense, all of it.

I just had one question, why are the modes unstable, and If they are, how do you go about creating a modal chord progression?

Modes are unstable due to tritones. The tritone is the interval of an augmented fourth or diminished fifth, which are each other's inverses and enharmonic equivalent. It is a very dissonant interval due to the frequencies relating to each other in an irrational manner. Their ratio is √2 : 1. A scale which has one of the notes of its tonic triad involved in a tritone relationship with another scale tone will not be stable. The Ionian and Aeolian scales both do not have this problem, but all the other modes will. However, as the Ionian and Aeolian scales correspond to the major and natural minor scales, they are only really limiting to use modally, as it results in much more rigid music. The other modes can be used, but they will not pull to the tonic, and thus are not stable enough.