In ABRSM grade 5 theory you are normally asked to work out the key of some music without a key signature. You are given four key options for each melody.
- Look at the major key options and make a note of the sharps or flats in each one.
- Look at the minor key options and make a note of the 3rd degree of the scale (mediant note) and the raised leading note (7th degree of the scale, which should be one semitone lower than the keynote, and one letter lower in the musical alphabet). These two notes are sufficient for working out a minor key.
Check the melody against the sharps/flats and mediants/leading notes you have noted down, until you find a match.
Here are some examples.
1. What key is this melody in? Is it Bb minor, Db major, Ab major or Eb minor?
Check each key in turn, looking for the notes mentioned above.
Bb minor: third=Db, leading note=A (natural). This must be incorrect, because the melody uses Ab.
Db major: 5 flats (Bb-Eb-Ab-Db-Gb). This must be incorrect, because the melody uses G.
Ab major: 4 flats (Bb-Eb-Ab-Db). This must be correct, because all the notes match.
Eb minor: third=Gb, leading note=D (natural). This must be incorrect, because the melody uses G natural and Db.
2. What key is this melody in? Is it Bb minor, Db major, Ab major or Eb minor?
Bb minor: third=Db, leading note=A (natural). This must be correct, because both notes match.
Db major: 5 flats (Bb-Eb-Ab-Db-Gb). This must be incorrect, because the melody uses A natural.
Ab major: 4 flats (Bb-Eb-AEb-Db). This must be incorrect, because the melody uses A natural.
Eb minor: third=Gb, leading note=D (natural). This must be incorrect, because the melody uses Db.
3. What key is this melody in? E major, C# minor, F# minor or B major?
E major: 4 sharps (F#-C#-G#-D#). This must be incorrect, because the melody also uses A#.
C# minor: third=E, leading note=B#. This must be incorrect, because the melody uses B natural.
F# minor: third=A, leading note=E#. This must be incorrect, because the melody uses E natural and A#.
B major: 5 sharps (F#-C#-G#-D#-A#). This must be correct, because all the notes match.
4. What key is this melody in? F# major, C# minor, F# minor or B major?
F# major: 6 sharps (F#-C#-G#-D#-A#-E#). This must be incorrect, because the melody uses A natural.
C# minor: third=E, leading note=B#. This must be incorrect, because the melody uses E# and B natural.
F# minor: third=A, leading note=E#. This must be correct, because both notes match.
B major: 5 sharps (F#-C#-G#-D#-A#). This must be incorrect, because the melody uses E# and A natural.