Key signature

A key is the set of notes a song uses plus the home note, or tonic, they gather around. The key signature is how sheet music writes that down, so nobody has to put a sharp in front of every F in a G major song. One F# at the start of each line covers every F, in every octave, until the signature changes.

Sharps and flats always arrive in the same order, one at a time:

• Sharps: F# C# G# D# A# E# B#
• Flats: Bb Eb Ab Db Gb Cb Fb

So a two-sharp signature is always F# and C# (D major or B minor), and a three-flat signature is always Bb, Eb and Ab (Eb major or C minor). Two tricks name the major key. With sharps, go up a half step from the last sharp: after F# and C#, a half step up from C# is D. With flats, the second-to-last flat is the key’s name: Bb Eb Ab means Eb major. F major, with its single Bb, is the one you just memorize.

Each signature fits two keys, a major key and its relative minor. To tell them apart, check the last chord and watch for a raised 7th: a one-sharp piece full of D# notes that ends on Em is in E minor.

A sharp, flat or natural written next to a single note is an accidental. It overrides the key signature for that note only until the end of the bar.

Players who never read notation meet the same idea as “the key”. A song in G uses F# instead of F, which is why its D chord is D F# A. Every chords by key page shows its scale and key signature, G major for example, and the circle of fifths puts all 12 major keys in order.