Harmony: Minor Key: V/vi Common in pop songs

Since the ascending harmonic minor makes the dominant of the minor mode a major chord by alteration of the major scale from which it was derived, the resulting shift enables an important modulation. It is one that is very common especially in popular songs where the affect of lyrics changes from happy ( Major key) to sadder ( relative minor ). So the sequence V/vi - vi in the harmony marks the arrival in the relative minor. In the major key the degree based on the third degree is a minor triad, iii, or e-minor in C-major. By simply altering it to the corresponding major triad, E-Major, by raising the note G to C#, one gets V/vi or the dominant of the relative minor. In C major and in popular songs the modulation I, V/vi, vi is so common as to deserve mention, therefore. The reason I notate it as V/vi and not III, which would be the corresponding major triad on degree three, is to suggest its function relative to the relative minor. In Schubert's music where modulation by major third relations are common, one would use III because it is not preparing for modulation to the relative minor. This is possibly the beginning of non functional harmony.