5

It's very common to see in Bach's work, that he follows a particular scale but then in a special moment, uses a chromatic alteration. What I have observed is that he usually does it when reversing the direction of an arpeggio or making a quick transitional note.

Example:

Prelude from Cello Suite 1

Second example: Allemande BWV 996

What is the rationale behind these subtle deviations from the key?

  • Your second example is just utilizing the melodic and harmonic minor scales which is nothing special. – Dom Oct 1 '15 at 1:14
  • It is called modulation. – Neil Meyer Oct 1 '15 at 7:55
  • Again, neither of these examples show modulation. If the next several measures of the cello suite are in C major, then I suppose it might be, but I'm fairly certain the piece goes right back to G major, it's just a secondary dominant creating a measure-long tonicization. The second example is just e minor. – Pat Muchmore Oct 1 '15 at 13:14
  • Maybe not for the second one but that lowering of the F sharp clearly means the moving from G major to something else. – Neil Meyer Oct 2 '15 at 12:50
  • @NeilMeyer Chromatic alteration is not equal to modulation. Look up the piece: the G7 chord in the OP's example is a V7/IV. The next measure is the IV, and the very next measure is a V7 complete with a restored F#. A modulation would have to last for one than one chord for the term to have any meaning, otherwise every secondary dominant would be a key change. – Pat Muchmore Oct 2 '15 at 16:22
4

In addition to being a melody, this is also an outline of a harmonic pattern. I suspect Bach is using F natural in the second measure in order to create a secondary dominant chord, specifically V7/IV. Is the next harmony outlining a C-major chord?

EDIT: ok, I looked it up, it is indeed a V7/IV going to a IV chord. Secondary dominants are fairly common, powerful chromatic chords that intensify the harmony progression toward a harmony by borrowing the upcoming harmony's V chord. The IV chord in G major is a C major chord, so Bach borrows the V7 chords from the key of C major (G Dom 7).

FURTHER EDIT: You added the second example after this answer, so, for completeness sake, I'll put my comment up here: Your second example is in the key of e minor, so the D#s aren't even chromatic. That's just the raised leading tone of e minor, forming a garden variety V chord. The C# is also diatonic to e minor, it's just a raised submediant. The sixth and seventh scale degrees are raised so often in minor keys that it is barely even seen as an alteration.

  • A minor, apparently. It's bars 15-16 from the typical Cello prelude. – Alain Jacomet Forte Oct 1 '15 at 0:38
  • I'm beginning to doubt that was a good example of what I meant though – Alain Jacomet Forte Oct 1 '15 at 0:40
  • Nope, I just looked it up, it's C major in second inversion (G-C-E with an embellishing D neighbor tone. – Pat Muchmore Oct 1 '15 at 0:40
  • I added another example. The beginning of Allemande BWV996. Am I wrong to think there is a single logic behind these embellishments? Is each one a different case? Perhaps it's just me, but this happens all over Bach? – Alain Jacomet Forte Oct 1 '15 at 0:46
  • You're not giving much context with these examples, but I'm fairly certain your second one is in the key of e minor, so the D#s aren't even chromatic. That's just the raised leading tone of e minor, forming a garden variety V chord. The C# is also diatonic to e minor, it's just a raised submediant. The sixth and seventh scale degrees are raised so often in minor keys that it is barely even seen as an alteration. – Pat Muchmore Oct 1 '15 at 0:49

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