supertonic

The supertonic is the second degree of a diatonic scale, the note or scale degree that lies a major second above the tonic. In functional harmony, it is considered a predominant function that prepares the arrival of the dominant and, ultimately, the tonic.

The quality of the diatonic triad built on the supertonic depends on the scale form. In a major key, the supertonic triad is typically minor (ii). For example, in C major the supertonic is D, yielding the D minor triad (D–F–A). In natural minor, the triad on the supertonic is usually diminished (ii°); in A minor, the B–D–F triad is diminished. In melodic minor, ascending, the supertonic can form a major triad (II) due to the raised sixth and seventh degrees. The exact chord quality thus reflects the used scale variant.

Common usage emphasizes the supertonic as a pre-dominant function. One of the most familiar progressions is ii–V–I in major keys, where the supertonic chord leads smoothly to the dominant and then to the tonic. In minor keys, ii°–V–i is a standard alternative, with the dominant often altered to strengthen the resolution to the tonic.

Examples help illustrate the concept. In C major, the supertonic is D; in A minor, it is B. The term “supertonic” can also be extended to modal or non-diatonic contexts, but in traditional tonal theory it mainly denotes the second scale degree and its usual chordal function as a pre-dominant.