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I'm trying to decide the key changes in the Laudamus Te of the Mass in B minor (J.-S. Bach).

Laudamus Te

I think the key in the 8th measure is B minor (the Laudamus Te is in A Major), but I'm not sure what happens in the 9th measure.

It seems to be similar one tone lower, but is not in A minor. F, C and G are sharp, so it looks like A major, but what to say about the sharp G on the last beat?

Are there modulations that I'm not seeing?

2 Answers 2

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First of all the last G is natural not sharp because any accidental in the measure stays unless otherwise noted.

It seems like the harmonic rhythm is every two beats (i.e. the chords change every two beats). From the two measures you've shown we can see the chords created are:

F#  Bm7  | E  A7

The first part can be interpreted as V to i7 in B minor and the second part can be interpreted as V to I7 in A major. Without seeing more of the piece I cannot confirm if the piece actually modulates or if something else is going on. If the next measure uses chords more accustom to A minor in the next measure I would say it has modulated if it doesn't then probably not. For example I can see an interesting sequence coming out of this progression as all the chord are a 4th up/5th down from another.

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  • Yeah sorry meant sharp not flat. How can you be sure about F# without a E# in the first two beats? Commented Jan 9, 2015 at 21:35
  • @PierreArlaud An F# chord is made up of the notes F#, A#, and C#. If there was an E# then it could be interpreted as a minor 7th of an F# chord making it an F#7, but it is not necessary.
    – Dom
    Commented Jan 9, 2015 at 21:38
  • @PierreArlaud There are no flats in the two measures you posted and B is natural in both.
    – Dom
    Commented Jan 9, 2015 at 21:43
  • Sorry I'm at a point of high confusion tonight apparently. I meant that D is sharp in F# and here it's natural. Commented Jan 9, 2015 at 21:48
  • @PierreArlaud when I say the chord created is F# I mean the harmony seems to infer F#. It does not mean that every note in that section is in the chord or from the key of F#.
    – Dom
    Commented Jan 9, 2015 at 21:52
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I'd call it more F♯7 - Bm | E7 - A7, treated as V7 of ii - ii - V7 - V7 of IV. (Notice that G♮/G♯ never shows up in m.8.)

Bach is actually articulating every quaver, but using these as elaborations of the main harmonic rhythm, which is, as Dom says, every minim.

The pattern of the sequence at the quaver is | (m. 8 in "B minor") vii° - i - V7-6 - V - i - vii°6 - i6 - i |
(m.9 in A Major) V7 - (iii) - V6-5 - V7 - I - vii°6 - I6 - I7 |.

The 7th over the tonic in the 2nd half of the m.8 is thus a conventionally prepared and resolved suspension holding over the seventh, not a chord tone of the tonic. The F♯m (iii) chord I've marked in parentheses in m.9 almost acts more as a passing chord under the held E than independently, but it cancels F♯'s significance as V of ii.

What Bach has done in m.9 is intensify the sequential pattern by changing the accompaniment in the first half of the bar to

  1. recast the preceding bar as V of ii - ii (rather than V-I in B minor), and
  2. add a touch of ambiguity on the 4th quaver - in m.8, the D in analogous spot in the melody is a too-early resolution of the suspended 7th (given that it plays against C♯); in m.9, the C♯ that follows the suspended D could very well be a deceptive resolution (vi6), as the B that follows it is the only B in the harmony and acts more like a lower auxiliary -

and, in the 2nd half, by foregoing the suspension, instead dropping the turn motif a whole tone to undercut A as tonic and cast it as V of IV. You know that the chain of falling fifths is going to continue.

That's the beauty of Bach's music. This passage really exists on 3 levels:

  1. as 2 bars articulating a standard cadential pattern in A Major (V7 of ii - ii - V7 - I?), where the pattern is broken enough at the end to reinterpret the tonic as a dominant;
  2. as a falling fifth sequence on the minims; and
  3. by means of very subtle voice leading, as an active movement by quavers that melds the bars together through anticipation and restatement of harmonies (2nd and 6th quavers of m.8, 6th quaver of m.9); by changing the function of a root (2nd quaver and last quaver of m.9); and by intensifying the movement through ambiguous voice leading (4th and 7th quavers of m.9).

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