Key Signatures for Minor Keys
Some people are really surprised to find out that there's more than one key associated with the same key signature. For example, if the key signature is 3 sharps, we can't automatically assume that the key is A Major. There's at least one other key that uses 3 sharps, F# minor. (Actually, there are a total of 7 different diatonic keys that use the same key signature; let's just keep it simple for now!)
One approach to understanding key signatures for minor keys is a parallel approach. If we know the key signature for a major scale (such as C Major, or A Major, or Eb Major) we easily can find the key signature for the parallel minor key (such as C minor, A minor, or Eb minor): just add three flats to the Major Key signature.
- C Major = 0 flats or sharps; C minor = 3 flats
- A Major = 3 sharps; A minor = 0 flats or sharps
- Eb Major = 3 flats; Eb minor = 6 flats
A different approach that works just as well is the relative approach. Again, starting with the major key signature and scale, we find the sixth note of the scale (some people like using LA) and that becomes the relative minor scale of that same key signature; for example,
- The relative minor for C Major is A minor. They both use 0 sharps or flats in the key signature.
- The relative minor for A Major is F sharp minor. They both use 3 sharps in the key signature.
- The relative minor for Eb Major is C minor. They both use 3 flats in the key signature.
Clearly, everything in key signatures comes back to knowing the Major keys, just as everything in arithmetic comes back to knowing your addition tables!
An illustrated explanation is here.