Semitons

Semitones, also called half steps, are the smallest standard interval in most Western tonal music. In 12-tone equal temperament, a semitone is the distance between two adjacent pitch classes and equals 100 cents.

Traditionally, two kinds of semitones are distinguished. The diatonic semitone occurs between two successive notes of the diatonic scale (for example E and F, or B and C in C major). The chromatic semitone occurs between notes that share the same letter name but differ by a semitone (for example C and C#). In practice, these two are not always the same size, depending on the tuning system used.

Two semitones make a whole tone (major second). This relationship underpins many scales and harmony patterns. For example, the major scale follows a pattern of whole steps and semitones, with semitone steps occurring between the third and fourth, and the seventh and eighth degrees (in C major: E–F and B–C).

Sizes of semitones can vary with tuning systems other than 12-tone equal temperament. In various historical temperaments and in just intonation, chromatic and diatonic semitones may differ in size, and the exact cent value is not fixed. In microtonal and some non-Western systems, intervals smaller than or larger than a conventional semitone may be used, expanding the concept beyond the standard 12-TET semitone.