Supertonic in the context of "Primary triad"

In Western music theory, a major second (sometimes also called whole tone or a whole step) is a second spanning two semitones (Play). A second is a musical interval encompassing two adjacent staff positions (see Interval number for more details). For example, the interval from C to D is a major second, as the note D lies two semitones above C, and the two notes are notated on adjacent staff positions. Diminished, minor and augmented seconds are notated on adjacent staff positions as well, but consist of a different number of semitones (zero, one, and three).

The major second is the interval that occurs between the first and second degrees of a major scale, the tonic and the supertonic. On a musical keyboard, a major second is the interval between two keys separated by one key, counting white and black keys alike. On a guitar string, it is the interval separated by two frets. In moveable-do solfège, it is the interval between do and re. It is considered a melodic step, as opposed to larger intervals called skips.

The ii–V–I progression ("two–five–one", occasionally referred to as the ii–V–I turnaround) is a common cadential chord progression used in a wide variety of music genres, including jazz harmony. It is a succession of chords whose roots descend in fifths from the second degree (supertonic) to the fifth degree (dominant), and finally to the tonic. In a major key, the supertonic triad (ii) is minor, and in a minor key it is diminished. The dominant is, in its normal form, a major triad and commonly a dominant seventh chord. With the addition of chord alterations, substitutions, and extensions, limitless variations exist on this simple formula.

The ii–V–I progression is "a staple of virtually every type of [Western] popular music", including jazz, R&B, pop, rock, and country. Examples include "Honeysuckle Rose" (1928), which, "features several bars in which the harmony goes back and forth between the II and V chords before finally resolving on the I chord," "Satin Doll" (1953), and "If I Fell".

The half diminished scale is a seven-note musical scale. It is more commonly known as the Locrian ♮2 scale or the Aeolian ♭5 scale, names that avoid confusion with the diminished scale and the half-diminished seventh chord (minor seventh, diminished fifth). It is the sixth mode of the ascending melodic minor scale.

In the key of B♭, the half-diminished scale built on C is associated with Cm, which functions as a ii chord in minor (see chord-scale system).