
Originally Posted by
JonR
It means lowering the scale degree, but it results in the same thing, I guess.
So "II" means a chord built on the 2nd degree of the scale.
"bII" means we flatten that scale degree and build a chord there.
So a "bII" in A minor means a Bb chord. If it doesn't say "m", and is in caps, we assume it's a Bb major chord.
There are various systems of roman numerals: some use caps and lower case to distinguish major from minor; some use all caps with "m" for minor; some just use caps and expect you to know what kind of chord it is (eg you should know that "II" in a major key is a minor chord, so there's no need to label it as such).
Here's the chords in a major key, described in the different systems:
I ii iii IV V vi viidim (or viio)
I IIm IIIm IV V VIm VIIdim (or VIIo)
I II III IV V VI VII (the classical convention)
Likewise, some people use "b" when listing the chords in a minor key, some don't - because you're expected to know, eg, that "III" in A minor is a C chord, not a C# chord! Here's some ways of showing chords in a minor key:
I ii III iv V VI viio
I ii bIII iv V bVI viio
I II III IV V VI VII (yep same as major, you would know from the context whether the key being discussed is major or minor)
Of course, the big problem with minor keys is the difference between G and G#dim in A minor. What does a plain "VII" mean in a minor key?
If you call G#dim "VII" (or "viidim"), you have to call G "bVII". So maybe then you should call C "bIII" and not "III"?
Or should we call G#dim7 "#viidim"? I'm not sure if there is any conventional agreement on this.
What does matter is that you don't mix different systems. So there's no need for "iiim", eg. At the same time, don't use both "IIm" and "iii".
It gets complicated when keys borrow chords from other keys and modes.
Eg, if you're in the key of A major, you might sometimes see G or C chords. These have to be described (IMO) as "bVII" and "bIII", to distinguish them from the diatonic G#dim and C#m.
If you're in the key of A minor, you might see a D major chord. If we already label every chord in caps (no "m"), because we know the "IV" is always minor, what happens when it isn't? Do we call D "IVmaj"?
Again, I don't think there is an agreed convention, and I suspect most people (at least non-classically trained ones) will prefer the use of either lower case for minor, or adding "m" to the caps. And maybe also using "b" for the bIII, bVI and bVII chords in a minor key, so we relate everything back to major as standard. I think this is the most sensible system, as it avoids all confusion (or at least avoids confusion better than the other ways).
Just be aware of the variations!