"Golden Train" by Justin Nozuka (YouTube link below) is in the key of Ab major. However he uses a Cb major chord throughout the song, which is not in the key of Ab major. It sounds good and works well for creating tension, but I want to know why it sounds good if it's not in the key. Pay special attention to the word "away" in the chorus, that is the Cb chord I'm talking about.

The progression in the chorus is Ab Cb Bbm.

  • Is the sheet music for this available to view anywhere?
    – Noldorin
    Jun 9, 2011 at 17:05
  • In music theory, the G (major/minor) chord is simply the mediant chord of the E major/minor key. The tonal separation of a third is generally considered to be harmonic. There may be something more here, but I can't tell without seeing the sheet music.
    – Noldorin
    Jun 9, 2011 at 17:10
  • 3
    @Noldorin the mediant is diatonic, meaning it would be G# in the key of E major. Jun 9, 2011 at 17:16
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    I've edited the question to refer to the chords that sound, since this is a theory question and guitar is not a transposing instrument.
    – NReilingh
    Jun 9, 2011 at 19:10
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    @NReilingh Luckily, I used roman numeral notation (mostly) so my answer (mostly) stands. Although, technically, since this is a theory question, the actual notes aren't that important. ;) Jun 9, 2011 at 19:28

1 Answer 1


The ♭III is a borrowed chord from the parallel minor.

A bit more info: The bIII is commonly followed by the IV, giving it something of a subdominant function relative to the IV. The ii here is acting as a IV (it's the relative minor of IV) in a plagal cadence, so functionally what we have is more similar to I bIII IV, a common rock progression.

Also, the bIII can provide a particularly bluesy sound to an otherwise diatonic progression since it gives a minor pentatonic feel. Eric Clapton was fond of it as well.

Keep in mind that theory is descriptive, rather than prescriptive. Our brains are wired to hear certain sounds as consonant and dissonant, as creating or releasing tension, etc. There's a pretty good chance that Justin picked a bIII because it sounded good or because another song used it, rather than because he wanted to borrow a chord from the parallel minor. Nothing against Justin, he's a great songwriter. This is just how people usually work. However, knowing the theory does help broaden your palette of chord choices.

  • Interesting. It could well be this! I did noticed the enharmonicity of the respective major and minor cords, but didn't know this had a technical name.
    – Noldorin
    Jun 9, 2011 at 17:11
  • The questioner may also just be mistaking the "G chord" for an inversion of the tonic E chord.
    – Noldorin
    Jun 9, 2011 at 17:11
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    An inversion of the tonic E chord? The tonic E chord is a major chord, which has a G#. The chords in the chorus are E G F#m, or I bIII ii. Jun 9, 2011 at 17:15
  • @Noldorin, you could be right. However, I play this on the guitar and the G seems to fit perfectly with what he's playing.
    – balentaw
    Jun 9, 2011 at 17:15
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    @Noldorin Well, he said that G is not in the key of E, which is true of E major but not of E minor. If the key had been E minor, my entire analysis would have been wrong as the G major chord is diatonic. Pedantic man, away! Jun 10, 2011 at 0:35

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