Unlike the major scale, three different minor scales exist.
Composers will often merge two of these scales, natural minor and harmonic minor, for a more pleasing sound.
Recall the diatonic triads of both scales.
Notice that many of the triads are the same.
Three pairs of triads (III – III+, v – V, and VII – viio) are different due to harmonic minor's raised seventh degree.
III is prefered to III+. This is because III+, being an augmented chord, has a peculiar sound.
V is preferred to v since V contains a leading tone (and therefore is stronger). This does not mean that v cannot be used.
V is preferred to v since V contains a leading note (and therefore is stronger). This does not mean that v cannot be used.
VII and viio are both used equally. As you will later learn, each has a different function.
The merged minor scale contains nine different diatonic triads.