Could anyone please tell me the theory behind this progression. Why does it work

[tomp86]

Hi guys. Could someone please help me explain why the chord progression in the picture attached works. The part Im not so familiar with and looks quite interesting and strange is the vi (cm) to vii dim7 (dm7b5) to iiisus4 (gsus4) to V/vi (G) to I (Eb).

Side question: the progression Isus4 to vi is also new to me. Is there any theory behind it?

[quantum]

Can you give more context into this progression.  What is the melody to be used with it?  What is the bass line to be used with it?  Are these all root position, or are there inversions that have not been indicated?

[tomp86]

Can you give more context into this progression.  What is the melody to be used with it?  What is the bass line to be used with it?  Are these all root position, or are there inversions that have not been indicated?

Hi quantum. I've attached a new picture that shows the melody column names (sorry didn't realize I omitted it) and also the sheet music for the easy version. I wrote chord names above bars. I believe some of the chords may be in inversion form from looking at the sheet music baseline.  Can you shed any more light on the progression for me?  Thank you very much in advance. Tom

[tomp86]

I believe I worked out why most of this progression works

vi (cm) to vii dim7 (dm7b5)    this works as all the notes are just stepping up 1 interval (vi to vii)
vii dim7 (dm7b5) to iiisus4    this works cause vii is the dominant of iii (but in its diatonic diminished form and iiisus4 contains the 4th which matches with the 7th of vii dim7)
iiisus4 to V/vi (G)   this works as its just resolves the iiisus4 to iii but its also V/vi which is used in the next progression
V/vi to I (Eb)   this works as I contains the 3rd and 5th notes of the cadence our ears might be expecting (V/vi to vi)

Side question

Isus4 to vi I think this just works as the Isus4 is like a sus6 suspension that resolves done to the 5th in vi

[danesi]

is the vi (cm) to vii dim7 (dm7b5) to iiisus4 (gsus4) to V/vi (G) to I (Eb).

Side question: the progression Isus4 to vi is also new to me. Is there any theory behind it?

First question is answered by saying: It’s a secondary dominant. Everything is fun when you add a secondary dominant. (More seriously, vii is the 5 of iii, so they resolve into each other. G sus can easily resolve to G since it’s a diatonic step. The iii-I step is somewhat common (even though Eb isn’t technically the ‘I’ in this secondary dominant. Perhaps there is a ii-V in passing notes? I haven’t checked your attached score.)

Second question: Isus4 - vi is literally an interrupted cadence, but with a raised 3 in the tonic. I guess it sounds jazzier than the standard I-vi.

I hope you bear in the mind that I’m not at all a music theorist or jazz player. I’m a classical musician through and through and was using a classical analysis to help answer your questions. Hope it helped, though!

[tomp86]

Thank you for your analysis danesi. I think you might have missed my post above where I did a detailed analysis of each step in the progression. Im pretty sure its right was going to get someone to verify.  I believe your first paragraph analysis looks correct however Im not sure I agree with the interrupted cadence part as my understanding an interruppted cadance is a V to vi  not I to vi

[quantum]

I've listened to a few recordings of this, here are my ideas of what is going on.  Annotated score is attached.  As theoretical analysis is akin to performance interpretation, somebody else may come up with a completely different yet valid explanation. 

Using the score provided above, Bar 20-22.  Short tonicization into Cm, where the Dm7 and G chords are sourced from.  The G chord does not resolve, as it is a half cadence.  Immediately return to the home key of Eb. 

Bar 28-30.  Again a move from Eb to Cm.  This time a deceptive cadence from G to Ab.

Bar ??-??.  The third time is actually the focus of this group of cadences, it is the arrival into the chorus with the G finally resolving into Cm.

These three cadences work as a compositional unit, and all suggest a resolution to Cm.  The first instance leaves the resolution up in air, the second gives us more Cm tonality but avoids the Cm chord in favour of a deceptive resolution to Ab.  The third finally gives the ear the resolution from G to Cm and times it with the start of the chorus.  This gives the chorus entrance a very prominent place in the harmonic movement with the V-I cadence.

Here's a recording we can listen to hear these three cadences, along with the equivalent bar numbers from the example provided above.

0:46 Half cadence (Bar 20-22)
1:01 Deceptive cadence (Bar 28-30)
1:16 ii-V-I cadence (next page)