Over the Christmas break I heard this programme on BBC radio: Shine On You Crazy Diamond

David Gilmour discusses his famous four-note motif B♭ F G E but what wasn't discussed and I wished had been was the first three chords of the song, which are:

Gm G♭ B♭

In the first chord, the minor third of the chord is a B♭ note, which then serves as the major third of the subsequent G♭ major chord.

And I see that Gm is the relative minor of B♭ major. But what function does each chord serve? Is there some sort of cadential preparation going on? It sounds nice, but not like classical harmony to me.

  • 6
    Truly strange: The moment I saw that question in the "Hot Network" sidebar, the song was actually running on the radio...
    – ccprog
    Jan 2, 2019 at 14:43

7 Answers 7


The move from Gm to GbM is definitely not a standard “classical” progression, although it does start to happen more and more in the late Romantic era and in lots of Impressionist and other neo-tonal styles. It’s perhaps especially common in the triadic minimalism of composers like Philip Glass. I don’t think it’s super common in rock music, which might be part of why it sounds so fresh in the Pink Floyd example.

You’re exactly right that the “connective tissue” of the chord change is the Bb common tone. David Lewin called this move SLIDE, and neo-Riemannian theorists often call it P’ or “P prime,” because it’s the opposite of the connection they call P, which is short for parallel. P connects a major triad to its parallel minor counterpart and vice versa. This means the root and the fifth stay the same, and the third moves by a half step. P’ is the opposite, because, as you noted in your example, the third stays the same while both the root and fifth move by a half step. That’s why it’s the opposite of the parallel move.

Anyway, it’s an extremely cool sound, and it contributes a great deal to the moody effect of the beginning of “Shine on.”

EDIT TO ADD: Sorry, I just realized you also asked about the move from GbM to BbM as well. This move also includes a common tone—notably, the same Bb common tone as the previous move—and half step movements in the other two voices just like in the P’ move. Different voices and directions are involved though. The move is called a “chromatic mediant,” and that’s the name for any two chords with roots a third apart and the same quality (major or minor). There are many questions on the site that explain chromatic mediant a if you want more details.


I had some trouble finding the part of the "song" you asked about. I assume it is this part starting at 4:59:


The tonality is G minor (I suppose G aeolian if you want to get picky.)

...what function does each chord serve?

If we are wearing our music theory hats, function means identifying the chords within a key and the harmonic roles of tonic, pre-dominant, or dominant.

This is how I labelled it...

    Gm         |Gb   Bb     |Eb dm cm Bb |F           |
Gm: i          |?    III    |VI v  iv III|VII         |

Right off the bat we see there isn't a dominant function. There isn't an actual V or viio. That isn't unusual in rock music. But it lets us know we are using a different playbook than that of classical harmony.

Of course the question is about the Gb major chord.

Technically it's non-functional, because it isn't a chord from the key or a closely related key.

As @PatMuchmore points out Gb is a chromatic mediant of Bb. You might also say it's a chromatic passing chord, because of the step-wise motion connecting the chords. Although the bass moving by roots sort of undermines the idea of a passing chord. Also, the chord is harmonically important so calling it 'passing' isn't really appropriate.

If Roman numeral symbols is the concern, there isn't one to give it. Either skip it, or just write Gb or 'chromatic mediant` under it.

It's worth noting that while many times a chromatic mediant chord is often a borrowed chord (like C and Eb in C major where the Eb is borrowed from C minor) in this case the Gb is not a borrowed chord.

Significantly, the Gb could be respelled F# in which case it becomes a non-functional chord built on the leading tone. In classical harmony that leading tone chord would be a diminished chord and strongly indicate the key. But that doesn't happen here. So while these chords on the whole are diatonic the progression eschews basic classical harmony.

Of course, calling Gb non-functional should not be misconstrued to mean 'bad', 'wrong', 'weak', 'unimportant', etc. This chord creates the whole psychedelic feel of the progression. Without it the progression would be plain diatonic.

  • I'd say: by Gb the song is modulating to the relative key of Bb. Gb is as simple mediant chord, bIV, borrowed from the minor subdominant Ebm of Bb. (s. my answer) Aug 4, 2021 at 12:34

Although Michael Curtis said otherwise, I would argue that this is a borrowed chord.

Basically the G♭ is used to give the move to from gm to its relative major B♭ the character of a proper modulation like you'd find in classical pieces. If the progression were just something like

gm     E♭ - B♭
(/gm) |  - 

or even

gm     F  - B♭
(/gm) |  - 

then the B♭ would sound just like a with a clear expectation of dropping right back into gm. If we instead make it

gm     F₇   - B♭

then this changes somewhat: the F₇ is a more forcing dominant, and now it sounds more like

(/gm) | (/B♭)₇ - (/B♭)

Thereby, the B♭ chord effects a more prominent “opening up”, really places us in a major mood instead of just tossing in a major sound into the minor key. But the ₇ - resolution is a bit too much of a classical cliché and would feel rather out of place in this piece.

What Pink Floyd do instead is cleverer: seen from the target key B♭, a chord is burrowed from its parallel key, i.e.

gm      G♭    -  B♭
(/gm) | ♭Ⅵ(/B♭) - (/B♭)

with the ♭Ⅵ burrowed from the key of b♭-minor, i.e. we could also write.

gm      G♭    -  B♭
(/gm) | (/b♭m) - (/B♭)

This reinforces the opening-up character further, because if we're effectively coming from the key of b♭m then the B♭ major chord has something of a Picardy third effect. I could lean further out of the window and say this foreshadows the clear Picardy-third ending of Part Ⅸ of the piece, but that's probably a bit too much of a leap.

That B♭ is a common tone to all these chords is certainly a relevant observation too, but I don't feel this is really important for the progression. I don't intuitively hear any pedal-tone effect in this part of the piece.

  • I had a similar thought along the lines of your analysis. Bb as the center. The melody dwells on Bb and then also the final F chord of the phrase would be a sort of dominant. In the end I stayed with Gm as center given its use through out the rest of the other parts. Jan 2, 2019 at 13:48
  • I agree the key of the piece is definitely gm, but I've always found the B♭ chord to sound very sweet and homely there. Never really knew why, but when I thought about it for this question the burrowed-chord / Picardy-third interpretation jumped right at me. Jan 2, 2019 at 13:54

The loveliness is the ambiguity of morphing from tonal center of the the relative minor (G-) and relative major Bb. Starting on G- makes G- sound like the tonal center, but GOTCHA! you are in Bb!

G- (Six minor), Gb (flat six), Bb (One)

VI-, bVI, I

In fact the whole phrase ends on F (the Five chord of Bb), then, instead of returning to Bb (I), whoops! the G- (VI-) is a common replacement (re-harmonization) of the Bb tonic (morphing back to relative minor being the tonal center).

A beautiful thing indeed.


  • 1
    ...In B♭, G♭ is ♭VI, not ♭VII. In fact, OP's question is about the explanation of the G♭ chord specifically.
    – user45266
    Apr 24, 2019 at 22:21
  • I fully agree with this explanation: the progression |Gb Bb |Eb dm cm Bb |F is leading to the dominant of Bb=F, resolving to the relative Gm = vi, which is the tonic of the whole piece. So like many pieces are modulating in the relative minor key this song here is modulating in the middle section to the relative major key. Aug 4, 2021 at 12:44

In my opinion this is a borrowed chord! Why do you hear this passage still in Gm? I'm interpreating it in Bb (the Gb chord "shows" definitely a modulation to the relative Bb key - for my ears:

Let's say Gm is the vi degree of the relative key Bb, then we have:


So I'd say - transwriting Michael Curti's answer:

Gm |Gb Bb |Eb dm cm Bb |F | = Gm: i |? III |VI v iv III|VII

Gm |Gb Bb |Eb dm cm Bb |F | = Bb: vi|bVI I|IV iii ii I|V


Guys I studied music theory/classical guitar, beginning when I was 15 years old and continued through college in the mid 90s. After not playing for almost 20 years, I recently started playing again two years ago. Pretty much the short version of me. After studying this (particulary the live versions) for a couple days, I came to my own conclusion --whether accurate or not-- that this is a case of the harmonic minor being used. I haven't seen anyone else comment about this anywhere yet. I can't speak too much on the album version, so maybe this is something that happened later, but i'm looking at that Gb as an F#, and it's all over the place in the song. In the hook, Gilmour plays the Gm, then what i'm calling a Bb+/D III+ (first inversion, definitely enharmonically speaking, if you will) to Bb:


[Hook] Gm/D...You were caught in the crossfire Bb+/D...Of childhood and stardom, Gm7...Blown on the steel...C9...breeze. Eb...Come on you target for...Edim...faraway laughter, Bb...Come on you stranger, you...Dm...legend, you...D7...martyr, and ...Gm...shine

The Gb Major, which i'm calling F# Major (errrm, not sure about where the C# in the chord fits in), the Bb+, and the D7 are all screaming harmonic minor to me. Is there anything egregiously wrong with looking at it this way that i'm missing?



  • 1
    I don't see what you gain by trying to force this into harmonic minor. The Gb that you seem to be calling a Bb+/D has a Db in it (on the recording), making your interpretation problematic. In any case, this is a pretty common harmonic device that doesn't need to be tied to some encompassing scale; it also shows up at the end of John Fahey's recording of "Bicycle Built for Two."
    – user39614
    Jun 27, 2019 at 19:08
  • Ah, I see what you mean...I agree its the Gb during the verse parts. I've been watching an acoustic live version, and i'm pretty sure that's a III+ chord (well, augmented of some type at least) he's playing on this particular version during this part of the song: youtu.be/0qjpOLj7WSY?t=352 Jun 27, 2019 at 22:01
  • The chords I was questioning accompany "Remember when you were young/you shone like the sun" rather than the words you've quoted which come from later in the song and have different accompanying chords. Jan 13 at 16:31

"It sounds nice, but not like classical harmony to me."

And there we have it. There's a note in common, Bb. That's about all the 'theory' we're going to find to justify this progression (if we can call a non-functional series if chords a 'progression').

There's not really much more to say about the 'chromatic mediant' Gb to Bb either. There's a note in common. We've got a label for it because, yes, it sounds good and therefore people do it quite a lot.

I could dress this up with some more fancy labelling. But it won't give you a functional answer in the 'dominant resolving to tonic, tritone resolving to major 3rd' way of thinking. There's a common tone. That's it.

  • I agree here with you: There's not really much more to say about the 'chromatic mediant' Gb to Bb Aug 4, 2021 at 12:36

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