Codger,

the factor that defines whether a scale is major or minor is the quality of the 3rd note.

If it is a major 3rd it is a major scale.

If it has a minor 3rd it is a minor scale.

Its really that simple.

The arabic scale (5th mode of harmonic minor) is a major scale - it has a minor 2nd and a major 3rd.

"it is rare that a minor tune is not predominantly based on (and notated according to) the natural minor scale"

This comment simply isn't true.

Dorian, Phrygian, Aeolian, Harmonic minor and melodic minor all exist plentifully throughout all types of music.

How music is written is just how these things are represented in a visual form.


"I don't believe it makes sense to talk about "relative keys" for scales which have no common note set"

What you believe doesn't come into it.

The Key of Am is the relative minor of the key of C major.

In all functional harmony since about 1700, any piece written in the key of A minor will have a sharp 7th to make the V-I cadence more convincing.

This is achieved using either the Harmonic or Melodic minors.

This has been the fundamental cornerstone of western harmony since before 1700.