What harmonic resources underlie on Pink Floyd's “Brain Damage” song which make it so beautiful?

Question

Pink Floyd's "Brain Damage" is in the key of DMaj (I) , but the second arpegio chord (and perhaps the one that gives to the song his special sound) is G7 (IV7), whose 7th is a note that does not belong to any major mode. In fact this note (F) is the degree IIIm of the scale of D, so it should apparently clash with the Major feeling of the song.

I would like to know:

1. Some harmonic explanation, or at lest some justification of why this 'lawbreaking' sounds in fact so well.
2. Which are the effective resources the song uses in order to conciliate such Major-Minor inconsistency.

Answer 1

It does belong to a major mode. It's the Mixolydian mode. G Mixolydian contains all the G major notes with one exception - F♯ gets thrown out in favour of F♮.

Clashing with the 'major feeling of the song'? What? There are millions of songs that are ostensibly in major keys, but possess minor chords! Maybe you have the impression that major songs only contain major harmonies, and minor keys vice versa? That's just not a fact.

We often say that a particular song in a particular key can 'borrow' chords. That's just what's happened here. Diatonic chords from key D major are the mainstay, but - by borrowing from D minor, we then have access to the notes that constitute G7. Another 'excuse' would be to use D Dorian (D E F G A B C), which also facilitates use of G B D F.

Answer 2

"Everything must be a mode of the major scale" is a very rigid and narrow model of harmony, and it doesn't work when exposed to actual music.

Let's relax the concept of mode beyond "modes of the major scale", by making the following additional definitions. I'll call it Real Mode to distinguish it from the narrower idea that's better suited for simple exercises on theory classes.

• a Real Mode can be any set of intervals around a tonic note. It doesn't have to be found by rotating the major scale.
• Real Modes can be partially mixed to create new combinations or mixtures so that e.g. the intervals for degrees 1-5 come from one Real Mode and degrees 6-7 come from another Real Mode
• a Real Mode doesn't have to be completely defined, i.e. you don't have to know all the degrees for sure
• a Real Mode can be transitional, i.e. the feeling and set of intervals doesn't have to stay the same for the whole duration of a piece, it may last only for a brief moment

With these refinements we can say that the Brain Damage song is doing some modal mixing. It is making changes to the intervals around the tonic, the changes don't last very long and the scale degrees at each moment aren't completely explicated, so it leaves room for imagination.

If we further relax the concept of "mode" so that we don't have to have exactly seven notes per octave, then we have a practically applicable model of harmony that can be used for looking at actual music.

But the above is more like a theoretical description of what and how the song writers did. What comes to harmonic resources, the origins and inspiration of the music, I'd say that the list of ingredients probably has some blues. Nobody broke any laws there, just conventions and expectations.

For part 1 of your question, I'll interpret the question as "why does making changes to the harmony sound fascinating". I don't think I've ever heard any real explanation for this, that's just the way it is. When something about the harmony stays in place and other things move, it makes you follow what's happening and re-think the situation. Music is about finding a balance between the expected and the unexpected. Familiar, but not too familiar.