# Why does this modulation sequence work?

Here is the modulation sequence I have been using in my trio with 3 incomplete entries followed by 1 complete entry(I am currently at the third incomplete entry which ends on A before Dm suddenly comes back).

Dm -> C -> Bm -> G -> A -> D

I know how most of this is working. The Dm -> C is essentially modal modulation from Aeolian to Dorian except that it ends on a C chord rather than a Dm chord. The G -> A -> D is the classic IV -> V -> I cadential progression. But there is one area that puzzles me. That is where the Bm is. The progression from C to Bm isn't as simple as going down a half step because the third goes down a whole step. And the progression from Bm to G is puzzling me as well. It looks like the mediant being used as a pivot chord but is it really? I haven't used any diminished 7ths or Neopolitan chords or Augmented 6ths so far in my trio so it isn't a dissonant chord used as a pivot.

The Bm is also where the key signature changes which suggests that C is the pivot chord and not just a result of modal modulation. Overall, that whole area around Bm is confusing. Why does this modulation sequence work and what is going on around the Bm that is confusing me?

• I believe one way to understand Bm -> G is to think of it as D -> G (V - I in G) with a not-unheard of chord substitution of iii instead of V. Mar 13, 2019 at 20:12
• YouTuber 12tone recently did a good video about the mystery of the iii chord: youtube.com/watch?v=xhft-tgPw-w - perhaps the ambiguity of this chord makes it work well as the pivot chord in this progression. Mar 13, 2019 at 21:06
• Is this `Dm -> C -> Bm -> G -> A -> D` a sequence of key changes or a chord progression? Mar 13, 2019 at 22:22
• @ It is a sequence of key changes. It's just that I didn't know if the chord-progressions tag would also apply or not. I mean, the G -> A -> D still feels cadential in a way even if the actual ending cadence is well into the D major section. Same way with C major still sort of feeling like D dorian until it settles on the C major chord. Mar 13, 2019 at 22:27

OK, you want permission for the Bm chord? Yes, it's a bit of a 'sore thumb' if we listen with ears attuned to Common Practice harmony. But the F# leads nicely to the G in the following chord, and gives us a tantalising foretaste of the D major which is to be the final destination. We get to it through a walking bass line, which is always a strong feature. Voice it right and it will sound fine, if a bit 'modal'!

What did you want? A progression where every chord was the inevitable, predictable one to follow the last? How boring.

• Consecutive fifths! CALL THE MILITIA!
– user48353
Mar 13, 2019 at 21:48
• Yes, if you're in a harmonic world where parallel 5ths are considered naughty, the Bm chord might also be considered not to 'work'. :-) Mar 13, 2019 at 22:13

With the understanding that...

Dm -> C -> Bm -> G -> A -> D

...is a series of key changes, and then reading this comment...

The G -> A -> D is the classic IV -> V -> I cadential progression.

...I think you maybe conflating standard chord progressions with key change sequences.

Consider this: a common template of key changes in classical style for a major key composition would be...

`||: I V :||: ii vi I IV I :||`

The middle area after the double bar can be different, but typically minor, you could abstract it to...

`||: I V :||: ? I IV I :||`

...the `?` being the development section in the textbook sonata plan.

Most of those key changes when viewed as chord progressions would be roots by descending 4th. `I` to `IV` a descending 5th. `vi` to `I` an ascending 3rd.

Nothing horrible when viewed as a chord progression, but certainly `vi I` isn't a strong progression and `I IV I` is hardly an ending. Suffice to say I don't think the sequence of keys in that style depended on how they would work as a chord progression.

I will offer an alternate view. It doesn't come from a textbook. It's just my view on how I think that template worked as a common plan.

First let's distinguish two very important moves `I V` a descending 4th and `V I` a descending 5th. Two things so common we hardly think about them. The first is an opening. It creates an unrest, a forward impetus. The second is a closing. It creates a sense of repose and a conclusion. So we can say roots by descending 4th create forward impetus, descending fifths create repose.

If we return to the common plan, notice that the sequence of keys begins with opening moves which exploit forward impetus. The move `I IV` the descending fifth is not used until the end. It's very sensible to place the forward impetus at the beginning and the repose near the end. Using the subdominant (the `IV`) key at the end is so common in classical style, the feeling of relaxation so strong. I like thinking of that as the denouement which is borrowing a word from literature. This concept of opening lines followed by denouement is a kind of narrative view of the key changes.

Another way to view the plan of key changes is `V` and `IV` are the tonal degrees of the key and as such are like the tonal pillars of musical architecture. The `ii` and `vi` areas are the modal degrees and drift away from the primary tonality. To complete the architectural metaphor you could call those middle minor keys the arch supported by the pillars. That middle arch region drifts away from the main key but it is contained or supported by two solid tonal pillars.

So on a large scale view of an entire movement we can understand the sequence of keys with a kind of narrative framework or an architecture metaphor. You could come up with other descriptions, but the main point is the key changes don't need to reflect common chord progressions like `IV V I`. That clearly isn't fitting the standard classical plan.

Your design of key changes does not need to match up with a common classical plan. You can make your own design however you choose. But also you don't need to make it fit a chord progression. You can do that if you want, but it is not require by some kind of classical convention.

For example when you say it goes from `D` Aeolian to Dorian - dropping the flat - and then a cadence on a `C` chord. That suggests a kind of incomplete cadence and that surely would produce forward impetus. Seems good at the beginning.
You point out the `Bm` change is a puzzle. But what happens as everything unfolds? Does any thematic material from `Bm` get reintroduced in the final `D` major area? That could provide an effect of resolution in the vein of a recapitulation.
Starting and ending on the same tonic `D` certainly provides a traditional framing.