Accidentals - sharp or flat

• Feb 10, 2018 - 06:43

Hi everybody!
There is one thing I still can't understand - what kind of logic is behind picking up such or such accidental (sharp or flat). For example, in the piece of music below we see a F sharp as well as G flat. Why not to write F sharp or G flat in both cases? The tonality of this part of Mozart's fantasia is C major, I guess.

There is another example (see below Mozart's fantasia) - waltz from 'The Swan Lake' by Tchaikovsky. We see there a F double sharp instead of G natural. I wonder just WHY. The tonality is A major (3 sharps at the treble clef)

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There are a number of considerations that go into this, not sure how much music theory you know so I am not sure how much sense my explanation will make.

  • In basically stepwise chromatic line, the rule is to spell with sharps while ascending, flats while descending. This helps clarify the resolution of the accidental (F# to G, or Gb to F), and it also avoids the need for another accidental on the next note to cancel the previous one.

  • If the note in question is a chord tone, then the note should be spelled as appropriate for the chord. For example, in a D chord, we spell the note F#, but in a C diminished chord, we spell it Gb. In your example, the harmony appears to actually be something called an augmented sixth chord, and F# is the proper spelling here. but also, it resolves to G, to the F# spelling also applies because of the rule above.

  • Same principle for double sharps. In your example, the note is resolving to G# - a stepwise resolution. Spelling it G would require a courtesy sharp on the next note, and it would also be less visually obviously what is going. Right now you can clearly see the line goes down (G# to Fx) then back up. This is a great aid to sight-reading. This happens a lot in minor keys where the leading tone needs to be spelled as a raised seventh degree instead of a flattened first degree.

Hope this helps!

In reply to by Marc Sabatella

Thank you for such an extended explication. However, the both note lines in Mozart's fantasia are ascending and nevertheless there is an E flat in the first one and G flat in the second (though in the first line there is F sharp instead of G flat). This puzzles a little bit :(

In reply to by Alex Kor

Well, the ascending/descending rule only applies to stepwise lines. The Eb in the first measure of the Mozart is not resolving by step. it is spelled Eb because the second rule - Eb is the correct spelling according to the augmented sixth chord that is defining the harmony at that point. The Gb in measure six is part of an Ab dominant seventh chord (the V of the Db major that follows), so again, it is being spelled correctly according to the harmony.

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