Semitone
Smallest step of the diatonic scale.
What it means
The semitone (German Halbton) is the smallest distance of the common tonal system: twelve semitones yield the octave. On the keyboard it corresponds to the path to the immediately neighbouring key, whether black or white. In the diatonic scale, semitone steps occur at two places, between the third and fourth and between the seventh and eighth degrees in major.
Musical use
Two kinds are to be distinguished. The diatonic semitone connects two different degrees, for instance E–F or B–C; it is written as a step of a second and is called a minor second. The chromatic semitone connects a note with its altered form, for instance C–C♯; it stays on the same degree and is called an augmented unison. On the piano the two sound the same, in the writing they mean different things: the diatonic semitone is a step, the chromatic one a colouring of the same note.
The significance of the semitone lies in its directional force. The close distance produces tension: the leading tone pushes to the root, the Phrygian second degree falls to the root. Where semitones lie in a scale therefore decides its character, and the differences between the church modes rest solely on this.
In just and in unequal tuning not all semitones are the same size; only equal temperament makes them equal to one another and thereby enables the enharmonic equation.
In the equal-tempered system it is exactly one twelfth of the octave, that is, 100 cents. In other tunings the diatonic and the chromatic semitone are of different sizes, which leads in the ensemble, especially with strings and singers, to fine differences in the intonation of leading tones.
Other names
Halbtonschritt (“semitone step”) stresses the melodic motion by a minor second, Halbton can also mean the distance as such. The diatonic semitone (E–F, different natural notes) is to be distinguished from the chromatic one (F–F♯, the same natural note).
Performance practice
Take semitones with leading-tone character close — that is the most effective device for convincing intonation. Watch the direction: semitones leading upward pull toward the goal, those leading downward fall. And, when learning a scale, first impress the position of the semitones; everything else follows from that.