C♯ minor
Key with four sharps.
What it means
C♯ minor is the minor key with four sharps in the key signature: F♯, C♯, G♯, and D♯. Its root is C♯, its relative major E major with the same key signature. In the circle of fifths it lies four steps on the sharp side.
Musical use
For pieces in minor, the key signature gives only the pool of notes of the natural form. The leading tone — here B♯ (German his) — never appears in the key signature but always as an accidental within the bar, produced by raising the B natural, which the key signature does not alter. Likewise, in the melodic form ascending, the sixth degree is raised, which brings a further accidental with it. In related contexts, for instance with secondary dominants, double sharps can occur.
The relative major E major shares the key signature; which of the two keys is meant is revealed not by the pattern of the accidentals but by the music — the final note, the emphasis on the tonic, and the appearance of the leading tone.
When working with older sources, the question of temperament arises: in unequal temperaments, remoter keys sounded different from the usual ones, and the traditional talk of the character of individual keys has its basis here. For string players C♯ minor lies less comfortably than the simpler sharp keys, because hardly any open strings are available.
C♯ minor is the relative key of E major and the variant key of C♯ major with seven sharps. The accidentals are F♯, C♯, G♯, and D♯; the leading tone B♯ is additionally notated in harmonic minor. On the piano the key lies well under the hand because of the many black keys. In the piano literature of the nineteenth century it is frequently encountered and is often associated with dark, serious expression. For string players, by contrast, it is less comfortable, because only a few open strings resonate along.
Performance practice
Say the four sharps aloud before playing and name the notes. Check in the score where the leading tone is raised — this stands only within the bar. And in chromatically dense passages, take care not to read a double sharp as a single sharp.