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In Bach's St. Matthew's Passion section 33, at measure 104, both the first and second chorus pause together all at once, and there is a key shift. But I don't know to what key the music is shifting to. Key signature simple has one sharp for F, and thus it can either be a G major or an E minor. Initially, it is in E minor, but then I don't know how the key shifts during the music. There are so many accidental adding to my confusion. Thank you for your help in advance.

The first picture is the beginning of the piece.

This is the beginning of the music

Second is where I think the key shift happens after the pause.

This is where I think the shift in key is made after the pause

Third is the end of the song, and I wonder if the key had shifted back to the initial.

And I wonder if by the end the key shifted back to the initial key

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  • The first picture is the beginning of the piece. Second is where I think the key shift happens after the pause. Third is the end of the song, and I wonder if the key had shifted back to the initial. Thank you in advance.
    – Song
    Nov 29, 2023 at 4:20

2 Answers 2

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Initially, it is in E minor but then I don't know how the key shifts during the music. There are so many accidental adding to my confusion

These accidentals arise, as they typically do in this period, from secondary dominants. This concept describes chromatic alterations that arise from temporarily treating some degree of the scale other than the root as if it were the tonic. For example, in C major you might have an F♯ as a leading tone to G, and if that is part of a D major triad or a D7 chord, you would describe it as the secondary dominant. In Roman numeral analysis, because G major is V in C major, you would denote the secondary dominant as V/V or V7/V.

So the F♯7 here is V/V in E minor. But the next chord isn't B major; it's B7. This is part of a circle of fifths progression. F♯7 leads to B7, then E7, A7, then (a diminished fifth) D♯°7. In Roman numerals this might be V7/V, V7, V7/IV, V7/♭VII, vii°7. You might argue for V7/V/V/V/♭VII, V7/V/V/♭VII, V7/V/♭VII, V7/♭VII, vii°7 but I don't think this adds any clarity.

The D♯°7 chord that ends this passage also serves as the first chord of the subsequent passage, which has a far faster harmonic rhythm. The bass line is in chromatic stepwise motion, so the chords are in various inversions:

D♯°7, E7 (in third inversion), A (first inversion), F♯ø7 (second inversion), B7, A♯°7, Em (second inversion), A♯°7 (first inversion), D♯°7, B7, Em, F♯° (first inversion), B7, and Em before the final phrase. In Roman numerals: vii°7, V7/IV, IV, iiø7, V7, vii°7/V, i, vii°7/V, vii°7, V7, i, ii°, V7, i.

This may seem a bit confusing, but basically the first three chords are a secondary cadence on IV, the subdominant; the following iiø7 can be either pre-dominant or dominant, so serves as a kind of pivot, because the next series of chords are all dominant (including the first-inversion i chord) or secondary dominant: V7, vii°7/V, i, vii°7/V, vii°7, V7. After this last V7 chord, we've arrived squarely back in the realm of E minor.

The trick with these progressions is to focus on the roots and, because these changes in harmonic center are quick, not to see them as true modulations but as brief secondary harmonies.

You didn't ask about the reason for these very active and unstable harmonic progressions, but for anyone who's wondering, they serve to portray in very dramatic terms the opening of hell mentioned in the text as the chorus calls on the powers of hell to destroy those who have arrested Jesus.

If you are also wondering about how Bach gets from the B minor cadence at the end of the duet and the B minor opening of the 3/8 chorus to the D major before the grand pause, I would suggest that you look at it once more with these concepts in mind and see whether you can make better sense of it. If you're still uncertain, perhaps another question might be in order.

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You need to take more pictures of the St. Matthew's Passion. The beginning and ending pictures are in E minor, but the middle picture's rough chord progression is G - D (implied I - V in G major) before the fermatas and F♯ - F♯7 after them (implied V - V7 in B minor given Bach's tonal idiom). In short, the middle picture is in neither the starting key nor the ending key, so the piece changed keys in between both the start and middle and between the middle and end, and you should take more pictures of key changes or you won't see the full key change story.

I have reason to believe the beginning picture isn't in the same section or movement as the other two (wrong meter, condensed score), though.

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    "Duetto e coro" -- duet and chorus. The Bach Gesellschaft counts them together as number 33; the Neue Bach Ausgabe calls them 27a and 27b.
    – phoog
    Nov 29, 2023 at 7:09
  • On re-reading my previous comment, I see that it can come off as a bit snarky, which isn't the intention at all. I just could not quite articulate any additional thoughts, but now I can: it looks to me as though the two sections are seen as parts of a single whole for a few reasons, among which is the fact that the first one ends, and the second starts, on the minor dominant, which is common for two sections of a single piece. It's also very unusual for the meter to change in the middle of a baroque piece, but not unheard of, especially for dramatic effect, as is certainly the case here.
    – phoog
    Nov 30, 2023 at 8:31

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