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If I am in C, I often use the bIII, bVI and bVII chords from the Cminor scale. However, in an A minor aeloian progression I can just as well use these same chords except since A minor is the i chord that means the 3 chords above will also need to change their roman numerals. So how do I number them?

EDIT: When using roman numerals for C major we have I, ii, iii, IV, V, vi, vii. Right? When we have roman numerals from A minor aeolian we have i, ii, bIII, iv, v, bVI, bVII right? Now, when we borrow from C minor like C, Ab, Bb, C those non diatonic chords also need roman numerals and would use I, bVI and bVII. My confusion comes when a song or part of a song is in aeolian mode. What if the Bb chord appears in A aeolian? Is it now a bII chord? The song is still in C major but there may be a bridge in A aeolian so how do I number the chords in the bridge?

  • I don't know if I understand this properly. You want to know the names bIII, bVI and bVII of C relative to A ? If so just "calculate" where the root of each of these chord is compared to A and name them accordingly. For instance, the bIII of C is Eb major, relative to A Eb is the bV or #IV, so you would call it so. As far as I know, we call chord name relative to the key (tonal center) we are in. Is that what you're asking ? – 021 Feb 7 at 15:06
  • There is a little bit of ambiguity when you say you can use the same chords just as well, do you mean bIII, bVI and bVII, or Eb, Ab, and Bb? It sounds to me that you might be misunderstanding the difference between parallel minor and relative minor. Do you know what I mean by that? Sorry, just trying to get a barometer of your present understanding of music theory so I can tailor a better response. – CodeKoning Feb 7 at 17:16
  • I updated my question. Please see again. – armani Feb 8 at 20:44
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It's unclear what you you mean by "these same chords." But I will just work through the two possible meanings to illustrate the Roman numerals.

If you mean chords identified by the same roman numerals, which means the same functional chords, then the actual roots change!

C: bVII bIII bVI are chord Bb major, Eb major and Abmajor

Am: VII III VI are chords G major, C major, and F major.

You can see the Roman numerals stay the same (although the flat was used for the borrowed chords in major) but the actual roots are different.

If you meant to ask how to put...

C: bVII bIII bVI are chord Bb major, Eb major and Abmajor

...into A minor and keep the same roots and chord qualities then...

Am: bII bV bI

...would be the Roman numerals where the flat prefixes the Roman numeral to show the chromatic alteration of the root from the key signature - like A lowered to Ab - and upper case indicates major chord quality.

I assume you didn't mean this second case, because it creates musical non-sense like a chromatically altered tonicAb chord while the key label is for A minor.

I think the principle thing you want to know is prefix Roman numerals with a sharp or flat to indicate an alteration of a root from the key signature.

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  • I added info into the question. Also you say that in Amin the G chord is VII but the G chord is actually a bVII isnt it since it is G not G sharp. In another answe over on this site. They number the major chords in aeolian bIII, bVI and bVII. – armani Feb 8 at 16:06
  • It depends of the particular Roman numeral system you're using. I prefer the style that prefixes sharp/flat for root alterations from the key signature. So, AM: VII doesn't need a flat, because the G is natural already from the key signature, whereas A: bVII is a major key, where the seventh degree is G# from the key signature, and the flat is a prefix to show the chord is lowered from the key signature. In this system bVII is indicating a borrowed chord. See Kostka/Payne Tonal Harmony for a textbook that uses this system. – Michael Curtis Feb 10 at 14:09
  • When a flat is always added to chords III, VI, VII it's probably a system that doesn't indicate a key with the symbols, in which case all symbols should be in reference to a default major key. – Michael Curtis Feb 10 at 14:13
  • You needed to make the distinction between being in Aeolian mode and using borrowed chords. Those ideas are mutually exclusive. The standard theory is chords are borrowed from a minor key when being in a major key. If you are in Aeolian mode like in the modal jazz sense, you don't need to borrow chords like bVII , they are already diatonic chords of the mode. – Michael Curtis Feb 10 at 14:17

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