Minor second
One semitone, the narrowest step of the system — the basis of every leading tone.
What it means
The minor second comprises one semitone and is thus the narrowest step of the common tonal system. In the major scale it occurs twice: between the third and fourth and between the seventh and eighth degrees. As a sonority it is the sharpest dissonance, as a melodic step the most effective means of connection there is.
Musical use
Its significance lies in its pull. The leading tone stands a minor second below the root and pushes upward; on this rests the cadence and with it the whole of major–minor tonality. In minor this degree must be specially raised to obtain the leading tone — from this arises the harmonic form of the minor scale.
Equally formative is the minor second above the root: in the Phrygian key the second degree lies only a semitone above the finalis and falls toward it; this sonority carries a large part of the music shaped by this mode.
As a sonority it appears in the suspension, which resolves downward, and as a building block of dense sonorities and clusters. In inversion it becomes the major seventh; both are the same relationship in a different register, but the wide seventh sounds more open than the closely lying second.
The minor second is to be distinguished from the augmented unison: both sound the same, but the former connects two different degrees, the latter alters the same note.
The minor second is the smallest interval of the tempered system. As a sonority it is a sharp dissonance; in a suspension or as friction it is used expressively. Melodically it shapes leading-tone steps, sighing figures, and chromatic lines. Inverted it yields the major seventh. The name designates, as always with intervals, two neighbouring degrees, thus for instance E–F, while the chromatic semitone E–E♯ counts as an augmented unison.
Performance practice
Take leading-tone steps close — closer than the piano plays them. Lead the minor second with direction: the goal note is arrival, the starting note tension. And practise singing this interval deliberately; it is more demanding by ear than its small size would suggest, especially downward.