The chromatic scale

The chromatic scale is every semitone in the octave, played in order — twelve notes, then the octave.

It is not a scale in the usual sense

Other scales are selections. A major scale takes seven of the twelve and leaves five out, and that pattern of inclusion and exclusion gives it a shape: a tonic, a leading tone, notes that feel stable and notes that want to move.

The chromatic scale excludes nothing. Every note is equally available, so none of them is home. It has:

• no tonic
• no key signature
• no characteristic sound to recognise

That is not a criticism — it is the definition. It is the raw material every other scale is carved out of.

Spelling it

Because it uses more notes than there are letters, the one-letter-per-degree rule cannot apply. Convention gives a practical answer:

• Ascending, use sharps: C C♯ D D♯ E F F♯ G G♯ A A♯ B C
• Descending, use flats: C B B♭ A A♭ G G♭ F E E♭ D D♭ C

The logic is that an accidental should point where the line is going. A sharp raises, so it suits rising motion; a flat lowers, so it suits falling.

In real music the spelling follows the harmony instead. A chromatic passage inside a piece in E♭ major will be written with whatever accidentals make the surrounding key readable — see enharmonic notes.

What it is used for

Passing notes. A chromatic note between two scale notes, played through rather than landed on. This is by far the most common use.

Chromatic runs. As a decorative flourish, or to build tension without committing to a key.

Technique. Chromatic exercises are standard practice material because they cover every note and every finger combination evenly.

Twelve-tone music. Early twentieth-century composers used the twelve notes as a deliberately equal set, precisely to avoid any of them sounding like home.