What a Key Is
A key is the note a piece keeps coming home to, together with the seven notes it draws on. When someone says a song is in G, they mean G is where it rests and where it wants to end.
- 1 home note
- 7 notes to use
- a signature on the page
which styles use it
Every style on this site
The home note
Play a major scale and stop on the second to last note. Something in you wants that last step. That pull is the whole idea of a key: one note the music treats as home, and six others that lean toward it in different amounts.
That home note is called the tonic. It is not the lowest note or the loudest note, it is the one that ends the argument.
What the key gives you
- A set of notes
In C major you use the white keys. In G major the same pattern starts from G, which turns one F into an F sharp. Those seven notes are what the melody and the chords are built from.
- A set of chords
Stack thirds on each of the seven notes and you get the chords that belong to the key. That is why songs in the same key tend to use the same handful of chords.
- A home to leave and return to
Almost every song sets up a home, wanders off, and comes back. Without a key there is nothing to come back to.
Reading it on the page
The key signature is the row of sharps or flats just after the clef. It saves writing the same accidental on every note, and it tells you the key before you have read a single note.
One signature covers two keys. Two sharps means D major or B minor: the same seven notes, a different home. Which of the two it is you hear rather than read, because the music will keep landing on one of them.
Major and minor on the same notes
Every major key has a minor twin that uses exactly the same notes, starting three half steps lower. C major and A minor share all seven. Nothing about the notes changes, only which one the music treats as home, and that alone is enough to change the mood completely.
When the key changes
Move the home note somewhere else and the whole set moves with it. A change of key partway through a song is called a modulation, and the smaller the change in notes, the smoother it feels. That is exactly what the circle of fifths is a map of.