Interesting ambiguity with roman numerals.

Axe_meister · January 2022

So I was playing around with the ii V I chord substitution to make a standard chord progression sound more Jazzy. Just an intellectual exercise.

So if I'm going to a major chord the numerals make sense, but if I'm going to a minor chord they don't really make sense.
i.e. the 2nd of a minor key is diminished, and the 1st is of course minor.
So if i took it as read, I'd have to minor a minor (would that be turning it into a major or a Sus2? and then major the minor.

Obviously if I went from C to Am the chord progression would turn into C Bdim E Am.

Just an interesting observation.

ArchtopDave · January 2022

I not exactly clear as to what you getting at. Whether you write a 251 substitution as 251 or iiVI doesn't really matter. It's just conventional ways of describing what's going on. You could append whichever you choose with Major or Minor to clarify things further, if you wanted to do so..

Your Minor 251 substitution of Am is incorrect, as it should be Bdim Em Am. However if you add 7th's, then strictly speaking you then have Bm7b5 Em7 Am7, though fairly frequently this gets altered to Bm7b5 E7 Am7, because this increases the amount of tension that needs resolution.

Axe_meister · January 2022

The reason I say that is because lower case ii usually means minor with Upper case being major. 251 would actually be a better way of expressing it

viz · January 2022

I'm unclear of the issue exactly, but if you're in A minor and you want to write a 251, using Roman Numerals with the upper case / lower case convention, then you have a number of options.

Firstly you have the "natural minor" way of doing it with the diminished 2 and the minor 5. Which is in keeping with the harmonised chords of the key’s relative major:

ii° - v - i, or
ii° - v7 - i

Or if, as ATD says, you chose to majorize the 5 chord to make the resolution to the 1 chord more effective, which is the "harmonic minor" way and probably the most common way in classical music, it'd be:

ii° - V - i, or
ii° - V7 - i

Despite this being the most common in classical music, it doesn't have a proper name - it's typically known as "a 251 in a minor key, except with a proper dominant, you know, like it's normally done".

And of course, you can do all of the above without diminishing the ii:

For example, you can keep the 5 as a minor chord, which would effectively be playing in Dorian, in which case you'd have:

ii - v - i, or
ii - v7 - i

Or you can majorize the 5 chord as before, but without the diminished 2, which would be the "melodic minor ascending" way, which is very common in modern (and classical) music, which would be:

ii - V - i, or
ii - V7 - i

They're all 251s in a minor key.

jpfamps · January 2022

V7 in a minor key I've always assumed came from use of the harmonic minor.

I've always assumed that the harmonic minor got it's name from is use in harmony......

Regardless, a very common ii V i (in Am7), is Bm7b5, E7b9, Am7.

The b5 in Bm7b5 and b9 in E7b9 are the same note (F) and this adds another semitone resolution to the 5th (E) in the tonic.

viz · January 2022

jpfamps said:

V7 in a minor key I've always assumed came from use of the harmonic minor.

Yup, that’s what I meant - sorry, I confused things with me "it doesn't have a proper name" - I meant people don't usually refer to it as harmonic minor - the proper dominant is assumed, because it's so ubiquitous.

Back to the OP; in case you want to taste the different flavours of the four 251 options I wrote, you could sing the 6, 7 and 8 of the scale while the 251 harmony happens underneath. Assuming you're in A minor:

For the natural minor ii° - v - i, you'd sing F G A
For the harmonic minor ii° - V - i, you'd sing F G# A
For the Dorian ii - v - i, you'd sing F# G A
For the Melodic minor ascending ii - V - i, you'd sing F# G# A.

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Interesting ambiguity with roman numerals.

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