Chord analysis of Rachmaninoff's Piano Concerto No.2 Movement 1 mm 86

I need help in analyzing the chords of Rachmaninoff's Piano Concerto No.2 measure 86. In the snippet below, the measure is encapsulated by a green box. . Score is from and can be found here.

EDIT : As suggested by NReilingh, here are my thoughts: I do know that the first measures in this segment (mm 83-85) is EbM7, Abdim7, Eb. The first beat of measure 86 consists of the notes C, Eb, G, Bb, so my guess is that it is a Cmin7/Bb chord. The third beat of measure 86 consists of the notes Ab, D, Gb, Cb, so my guess is that it is a Ab half-diminished chord.

• Can you edit the question to include your current thought process on the matter? What does it look like to you, and what is giving you doubts? Straight analysis (like a homework question) is generally off-topic, but it's much better if we can help you solve a problem. Oct 11, 2014 at 5:21

To my ear, the measure sounds like descending diminished 7th chords. Beats 1 and 2 f# diminished 7th and beats 3-4 d diminished 7th. (I'm not sure how Pat gets a d half-diminished chord with that c-flat so prominent, but maybe I've misread it.) On the first beat the g and b-flat are suspensions from the previous measure, which resolve down chromatically. They in turn are suspended (with a respelling of the f-sharp) and resolve down after beat 3.

The D-flat in the melody is a mode mixture which is ubiquitous in Rachmaninoff. This is the exact same kind of modal mixture you get in the big theme in the Moderato section of the last movement. That theme enters in B-Flat, but he introduces an A-flat into the melody over chromatic harmony. It's common in Rachmaninoff to move freely between the major and parallel minor.

• Oh man, you're right, don't know what I was talking about with that half-dim. I'll edit my answer, thanks. Oct 11, 2014 at 2:09
• No problem…given your credentials, I assumed I misread something or it was just an oversight.
– user13034
Oct 11, 2014 at 19:07

Interesting segment. I think that the second half of the measure can be heard as a D-diminished-7th in third inversion, and thus functions pretty normally as vii-dim-4/2 leading to the I6/4 of the following measure that isn't in your example. The Db in the top voice admittedly complicates that analysis, but I don't think it's dispositive. The first half of the measure is more problematic. On the one hand, it's clearly just a sequence, with precisely the same pattern as the second half of the measure but written a half-step higher (spelled like F#-diminished 7, but just as likely heard as an Eb-diminished 7). On the other hand, it does seem to have a possible hearing (underlined by Rachmaninoff's or the engraver's choice of F#) as a secondary vii of a G chord. This is strengthened by the D natural in the upper voice on beat 2 which could make a secondary V of G. The ultimate resolution to Eb is thus both a perfectly normal vii-I progression, with a hint of a deceptive progression due to the first chord's implication of a temporary G as tonic.

That's probably a bit of a stretch, but I do think it adds a interesting layer to the progression. For the most part, it seems to be more of an ornamental chord moving in sequence down by half step to a vii-4/2.

[Thanks to MarkM for the correction about the chord qualities.]