Semitones

Semitone, also known as a half step, is the smallest pitch interval in most Western tonal music. In the common 12-tone equal-temperament system, a semitone is the interval between two adjacent pitches, such as C and C#, and it equals 100 cents.

Historically, two kinds of semitones are described: the diatonic semitone and the chromatic semitone. The diatonic semitone occurs between two successive notes of a diatonic scale with adjacent letter names (for example E–F or B–C). The chromatic semitone occurs between pitches spelled with the same letter name but raised or lowered (for example C–C#). In 12-TET both types have the same size, but in other tuning systems they can differ.

In equal temperament the size of a semitone is fixed, and enharmonic spellings (such as C# and Db) represent the same pitch on a keyboard. In other tunings, those spellings can correspond to different pitches, and semitone sizes may vary.

Semitones form the basis of the chromatic scale, and their arrangement determines the pattern of intervals in major and minor scales. For example, a major scale follows a pattern of whole steps (two semitones) and half steps (one semitone), with half steps typically occurring between E–F and B–C in most keys.

Outside the common system, some musical cultures and contemporary tunings subdivide the octave into more or fewer equal parts or into microtones, where the concept of a single semitone may differ. Semitone remains a foundational concept for describing pitch distance, harmony, and melodic motion.