C♯ minor
The minor key on the tonic C♯. It has four sharps in the key signature and the same notes as E major. It is known above all through the first movement of Beethoven's Moonlight Sonata.
Four sharps, minor
The page Circle of fifths lists C♯ minor as the relative key of E major with four sharps. Relative keys share the key signature, the minor key begins three semitone steps below the major key. That explains why the key signature alone does not say whether a piece is in major or minor. See Relative key.
Natural minor
The same notes as E major, only the scale begins on C♯. The semitone steps lie between D♯–E and G♯–A.
Harmonic minor
The B is raised to B♯. The leading tone B♯ lies a semitone below the tonic, between A and B♯ the augmented second arises.
As in every minor key there are three forms. The raising of the seventh degree, here B♯, is, according to the article The leading tone, the means by which minor borrows the leading tone: in minor the dominant becomes a major chord. More under Harmonic minor.
Chords and cadence
| Degree | Natural minor | With B♯ (harmonic) |
|---|---|---|
| i | C♯m C♯–E–G♯ | C♯m C♯–E–G♯ |
| iv | F♯m F♯–A–C♯ | F♯m F♯–A–C♯ |
| v / V | G♯m G♯–B–D♯ | G♯ G♯–B♯–D♯ |
| VII / vii° | B B–D♯–F♯ | B♯° B♯–D♯–F♯, diminished |
The derivation of the diatonic chords is on the page Diatonic chords, with A minor as the example. The pattern is the same in every minor key.
The Moonlight Sonata
The sheet music archive holds the first movement of the Sonata No. 14 in C♯ minor. The sheet carries the movement name as “Adagio sostenuto” and the alla breve sign.
Piano
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Mondscheinsonate, 1. Satz Ludwig van Beethoven, Sonata No. 14 in C♯ minor, op. 27 No. 2 · piano · 5 pages
“Adagio sostenuto”, alla breve sign (¢), four sharps in the key signature. Above it, in italics, is the instruction to play the whole piece very delicately and without dampers, in the first bar a piano pulse in groups of three with triplets.
Common mistakes
- Confusing C♯ minor and E major: Both have four sharps, the ending and the tonic decide.
- Writing the B♯ as C: In C♯ minor the raised seventh degree is called B♯, otherwise C would occur twice.
- Spelling: Write the note letter as a capital and the mode word in lowercase: “C♯ minor”.
Continue on Maikstrings
Related terms
E majorC♯ majorRelative keyMinorHarmonic minorMelodic minorSharp keyAdagioTempus
Editor: Maik Krohm · reviewed on 3 October 2026
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