In Under the Bridge by Red Hot Chili Peppers, the introduction alternates between D and F# chords, with an E in between as a passing chord in some cases. There is also a g# passing note played over the D chord, and together with the g# in the E chord, it gives the introduction a Lydian feel.

But how would you interpret the F# chord harmonically? I can't explain it in terms of modes, because in terms of scale degrees the 5th of the I chord is the 3rd of the III chord, so the I and III major chords cannot belong to the same scale/mode. I can't explain it in terms of a modal import either (no mode sharpens the dominant note).

Of course you could just say that the F# is an altered III chord and be done with it, but I don't find that satisfying because that argument can be used for literally anything. So I'm wondering if there's a more satisfying harmonic explanation, especially as this progression actually sounds pleasing and not at all 'random'.

PS: I come from a classical music background and I'm new to thinking in modes, so please forgive me if the question is stupid.

4 Answers 4


There's a much more simplified explanation of the chord progression. Let's start off by looking at the notes of each chord:

  • D (D F# A)
  • F# (F# A# C#)

So if you want to just move between the two chords over and over again you would most likely see the notes move in this fashion:

D  -> C# ->  D
F# -> F# ->  F#
A  -> A# ->  A

Notice how only two notes in the progression are moving and they are moving chromatically? This has two distinct effects on the progression. The first being your not really moving even though you are changing chords and the chords themselves D and F# while not truly being the whole tone scale, give the dreamy/foreign of it due to moving a major chord up and down by a major 3rd and even the E major contributes to this. Both of these ideas together give you the feel for the intro which is kind of spacey and doesn't go anywhere

You also have to look at the next section which is squarely in the key of E major. Transitioning into the intro from the F#, you immediately feel the E as the tonic. You could then go back and say the D is from the minor or Mixolydian mode and call it a bVII and say the F# is borrowed from the Lydian mode making it a II, but that would be kind of a stretch due how the progression doesn't sound like it goes anywhere.

  • 1
    Looking at those notes I'm wondering if this piece is not written in plain old b minor.
    – Neil Meyer
    Commented Nov 16, 2015 at 6:57
  • 1
    @NeilMeyer The next section which takes up a good chunk of the song use the chords E, B, C#m, A, G#m.
    – Dom
    Commented Nov 16, 2015 at 7:08
  • I would also mention that this relationship is referred to as a Chromatic Mediant, which also happens to be the basis for Giant Steps, so you could check out how Coletrane utilized this harmonic relationship as well. en.wikipedia.org/wiki/Chromatic_mediant Commented Nov 16, 2015 at 15:34

I feel more of a resolve when the D moves to the F# chord, thus I will say that F# is the tonic here, which makes the D chord the NbII (Neapolitan flat II) of the V (C#). Although the NbII is typically in first inversion, it isn't forbidden to be in root, as it is here.

  • If we were in F#, wouldn't NbII be G? I would believe the D to be a bVI with the analysis of F# being tonic. Commented Nov 16, 2015 at 15:31
  • Here, I'm saying the NbII of the V. So if F# is the Tonic (I), C# is V and D would be the flat II of V. Commented Nov 16, 2015 at 16:05
  • Brining up a neapolitain in another key doesn't really make sense especially since the said chord does not function that way. If you're using a neapolitain and calling it that you want to go to V of whatever key that is or else you loose all function.
    – Dom
    Commented Nov 16, 2015 at 17:54
  • 1
    @CatherineSmith- My apologies, I guess I missed that yesterday. Makes a bit more sense but I would agree with Dom on this. Conceptually it could make sense to think of this or something else along these lines but it doesn't function as such, so I can't say that it makes the most sense to do so. Commented Nov 17, 2015 at 14:51
  • 1
    We could also consider the D to be like a German Aug 6, without the 6, that doesn't properly resolve to V after visiting the tonic but that's also a stretch. My best suggestion within considering this to be in F#, other than modal mixture, is to think of the D as a substitution for V. I would also note that we are dealing with Rock music, so it's very difficult to apply these Classical concepts, as the music on the whole does not conform to the Classical idiom, as well as being Modal and not Functional Harmony. Commented Nov 17, 2015 at 16:51

There's only so much you can conclude from two chords.

For the benefit of anyone not familiar with the tune, there is a run of notes between each chord. From D to F#: C# B A G# F#; and from F# to D: F# E D B C# D.

Clearly all notes belonging to the A major scale. Without the knowledge of this, B minor would be a good guess for the key, but in the key of B minor you would expect to see a G in the descending line instead of the G#.

As has been mentioned, to my ears the F# feels like home, so I'd say this little riff is in the F# aeolian mode, which all the single notes mentioned above belong to, with tonic chords changed to major chords, in a sort of Picardy third kind of way, if that's your thing. Certainly, if I was transcribing it, I'd go with three sharps.


Regarding only the introduction, D major to F# major, the chords are chromatic mediants. In terms of progressions this is static, as the chords just alternate. In classical style there are similar devices like I-IV-I, or I6/4-V-I6/4-V... or V7/IV-IV-V7-I over a tonic pedal, all of which simply prolong a single chord. So this intro prolongs the D major chord with a chromatic mediant before moving directly to the main key of the song: E major. I think this design fits well the lyrics. The intro sort of represents the singer's feeling of lonliness or separation.

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