Key signatures
Lesson 10 of 14 · Intermediate · Why a piece in G has F♯ everywhere.
Sharps written once
A piece in G major uses F♯ instead of F all the way through. Writing a ♯ before every F would be tiring to write and to read.
Instead, a key signature at the start of every line lists the sharps or flats once. They count for every note with that letter, in every octave.
G major: one sharp
One sharp, on the F line, means every F is played as F♯: all of them, lit below. That's the key signature of G major.
F major: one flat
One flat, on the B line, means every B is played as B♭: the key of F major.
No sharps or flats at all means C major (or A minor, as a later lesson shows).
More sharps and flats
Sharps are always added in the same order: F C G D A E B. So D major, with two sharps, has F♯ and C♯.
Flats go in the opposite order: B E A D G C F. B♭ major, with two flats, has B♭ and E♭.
Practice
Reading key signatures.
Play the note as the key signature says. Any octave counts.
A tune in G major: every F is F♯.
A tune in F major: every B is B♭.
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