Recognizing the key from the key signature · Keys and key signatures · Music theory
With sharps, the major tonic is a half step above the last sharp: with F♯ and C♯, D major. With flats, the major tonic is the second-to-last flat: with B♭,…
Recognizing the key from the key signature
With sharps, the major tonic is a half step above the last sharp: with F♯ and C♯, D major. With flats, the major tonic is the second-to-last flat: with B♭, E♭ and A♭, E♭ major. The exception is the signature with a single flat: F major.
With no accidentals, C major. Every key signature belongs to two keys, a major one and its relative minor. To tell which, look at the music, above all the ending and whether the leading tone of the minor key appears.
Major or minor: how to decide
The key signature leaves two candidates. To choose between them, look at several things, in this order.