It (212) starts and ends in Dm. The second phrase beginns with F-Bdim/D-C. This is a modulation into the key of C...but the melody doesn't sound like it is in the key of C at all. I don't see how the F chord with A in the melody could sound like the key of C at all. The harmonisation sounds good when I play it but I just don't understand why they chose to modulate to C. Then it goes to the key of Am.

Why did they modulate to C?

enter image description here

closed as off-topic by Tim, Tetsujin, David Bowling, guidot, Doktor Mayhem Aug 2 at 17:29

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    I consider this as off-topic. In any case the key signature is missing. – guidot Jul 29 at 14:24
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    Why has anyone upvoted this particular question? – Tim Jul 29 at 19:25
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    On topic or not ... I think this kind of modulation or chord progression is interesting enough for everyone here! Sometimes the rules of this SE are really peculiar! I‘m going to vote up too. The question could easily be transformed to fit in by asking: I don’t understand this chord progression. Can someone explain what‘s happening here? – Albrecht Hügli Jul 29 at 19:57
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    @Tim, I don't think this is a simple and straightforward case of identifying the key. There's some modulation occurring, which the OP identifies, but then the OP asks about conflict between the harmony and melody. To me it seems more complex than simply asking "what (single) key is this in?" – jdjazz Jul 29 at 21:14
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    @AlbrechtHügli Then please edit the question to make it on-topic and useful for future readers. – Your Uncle Bob Jul 29 at 22:18

GThis choral is in d minor. Your explanation is absolutely correct. Mind that F and d minor are related chords. This substitution enables the modulation (transition) to C and a minor, while the whole chorale stays in d. That‘s all.

Edit: there might be added that the tune probably has been before the reformation and originally in the dorian mode, but in this arrangement and harmonisation it has been adapted to d-minor.

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    So they took Dorian melodies and looked at them as if they belonged to tonal scales/modes? – Hank Jul 30 at 15:08
  • @Hank, yes. In some cases the original hymn tunes evolved with rhythmic changes and accidentals to make them fit into the major/minor key system and metered bar lines. – Michael Curtis Jul 30 at 15:42
  • You are simply refering to melodies that was Gregorian in origin? – Hank Jul 31 at 16:46

I think you mean these two chords...

enter image description here

...B diminished in the orange box and C major in the blue box. You could simply label that Am: iio6 III or I prefer Am: viio6/III III to show the secondary dominant function of the diminished chord. That isn't a modulation, it's a temporary tonicization of C.

I posted an answer mainly to get the image label to show what you're asking about. You question made little sense to me when I first read it, because you cut off the key signature and the phrases appear to be a half cadence in D minor and then a modulation and full cadence in A minor.

But, your question is "why?"

The two keys involved are D minor and A minor.

Let's look at the chords on the strong first beats of the bars.

After the half cadence in D minor, we get the F major chord. That is the relative major of D minor and would be a very common chord to play in the context of D minor.

The next chord B diminished takes us to the C chord. In the next key - A minor - C major is the relative major.

Then the proper cadence is essentially Dm E | Am or Am: iv V | i.

The harmony between the two cadences is basically working with the relative majors of the respective keys. So you could say the reason it goes to C major is to get the relative major of the second key.


It doesn't sound like a modulation to C major because it isn't one.

After the imperfect cadence ending on the A major chord, every note in the passage up to the next (perfect) cadence belongs to the A melodic minor scale. There is no restriction in common-practice harmony to using only notes from the harmonic minor scale, except in textbook harmony exercises for beginners.

Nineteenth-century harmonic theorists might have labeled the Bdim/D - C progression as a "passing modulation" to C major, but now the function of the Bdim chord would be described as a "secondary dominant" of the C chord.

If you call the Bdim/D - C progression a "perfect cadence in C major" to be consistent you should also call the C and the following F a "perfect cadence in F major." But it should be obvious that a describing the harmony like that doesn't correspond to what you hear, which is the only thing that matters.

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    'If you call the Bdim/D - C progression a "perfect cadence in C major"...' it shouldn't be called that, the bass doesn't descend a fifth to C ...and there's no phrase ending. The OP just mislabeled the progression as a modulation. – Michael Curtis Jul 30 at 15:34

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