Roman Analysis of “Ab B G” chord

I am currently analyzing a bit of music for homework which consists of four voices (string quartet).

It is in the key of G Major, but the chord that it ends on, is a Ab on the cello, B on the Viola, and G on both violins.

So that chord is Ab B G, does anyone know how I would figure this in a roman numeral analysis?

Here is the score

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can you give some information about what is leading up to this last chord? – Stephen Nov 1 '12 at 18:19
I second what @Stephen asks. If you could post a screenshot of the measures leading up to this point, it would be helpful in determining the function of the chord you're trying to analyze. – jadarnel27 Nov 1 '12 at 19:56
Are you sure you're not misreading a clef (or two)? I can't imagine a teacher assigning a roman numeral analysis on that kind of chord, ever. Supplying a picture or scan is encouraged. – NReilingh Nov 1 '12 at 23:32
The score has been added, thanks guys – Jace Man Nov 2 '12 at 11:04

The Ab in the cello part in the final chord of the music you posted is almost certainly a typo. The entirety of the piece aside from that is written with typical common practice harmonies that you would expect to see in a theory class.

The only context I would expect to see the music played as written would be a mistake on the part of the cello player or typesetter, or a bizarre piece of performance art that exists to make the audience cringe when the cello plays the last note. `IIbmMaj7` chords do not exist in Theory 101, and when you see that combination of notes in a theory class, you're not going to be calling it a `IIbmMaj7` chord anyway (you'll be calling it a `0-1-4` pitch class set).

It's supposed to be a G natural in the cello part, making the final chord a perfect authentic cadence on the `I` chord.

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Well that makes much more sense, I shall email the department and confirm, but many thanks! – Jace Man Nov 2 '12 at 12:42
I had not thought of the score being in error, but that makes perfect sense. +1 – American Luke Nov 2 '12 at 13:15
Just letting you know that it was confirmed to be a typo, thanks again! – Jace Man Nov 2 '12 at 16:49

When identifying a chord, I normally follow these four steps. Here, I have them written out with the specific steps for the chord listed in the question.

1. First, when identifying the roman numerals, we must identify the notes that appear naturally in the key. Here, the key of G Major naturally contains the notes, `G A B C D E F#`.

2. Identify the notes in the chord. Here, we have `Ab B G`.

3. Identify where these notes fall into the the natural ascending scale of the key. `A` is `II`. So, `Ab` would be `IIb`. `B` is `III` and `G` is `I`.

4. Finally, we find the name of the chord. So far, our chord is `IIb III I`. When we see a `IIb` with a `I` in the same chord, it usually means it is some sort of a seventh chord. Here, the `III` would be the (minor) third, making it a minor chord with a major seventh added. This forms an `IIbm(maj7)` (Ab minor with a major seventh added) chord in root position. The fifth (`VIb`/`Eb`) has been dropped by the composer because the ear will naturally "hear" it whether it is played or not.

So, our end result is `IIbm(maj7)`

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Thank you so much for your answer, very detailed and helpful. We have never figured any chords like this in class yet, so I'll have to check with my teacher, but thanks again! – Jace Man Nov 2 '12 at 11:05