Key ID and Chromatic Notes

The key signature at the start of a piece of music represents one major key, and one minor key. To work out whether the piece of music is major or minor, we can start by looking at whether any accidentals from the minor scale have been added to the music.

But while this method works for simple melodies which do not have any additional chromatic notes added to them, in a more complex melody, like this one (Haydn, Quartet in D, op76 no.2), we can see both C# and G# added as accidentals, so what is the key here?

What key is this?

The clues we should look for are:

  • The tonic and dominant being emphasised,
  • Satisfactory explanation for any notes with accidentals.

Assuming a key of F major, the Haydn excerpt begins on the mediant and submediant notes. The submediant note is repeated. The C# is difficult to explain, but the G# could be classed as a chromatic appoggiatura.

Assuming a key of D minor, the excerpt begins on the dominant and tonic, with a repeated tonic. The C# is a chord note (chord V, leading note), and the G# is a chromatic appoggiatura.

The prominent use of the tonic and dominant, plus the satisfactory explanation of C# and G# mean that the melody is in D minor.

Here’s another example (Haydn Symphony in Bb, no.102)

What key is this?

Bb major or G minor?

The case for Bb major: dominant-tonic start, held tonic for full bar, chromatic passing note C#.

The case for G minor: unraised leading note-mediant start, held mediant, chromatic passing note C#.

The piece is in Bb major.