Keys

In music, a key is the main group of pitches, or notes, that form the harmonic foundation of a piece of music. The main pitches used in a song are usually all from one particular scale, and this is where we name the song’s key from.

To save us from having to add all the sharps or flats each and every time when we’re playing in a given key, we use a key signature at the beginning of the music to make it easier to read. For example: Instead of writing a sharp in front of every single F, we just write one at the beginning which then tells the musician to play an F# every time an F note occurs in that piece.

If a song only uses notes from the C Major scale, it is likely that the song is “in the key of C Major”. This would mean no sharps or flats - C, D, E, F, G, A, B, C.

However, the A minor scale also has no sharps or flats in it, so if we read a piece of music with no sharps or flats indicated, it might also be in the key of A minor:

There are always two keys that share the same key signature. The key signature is what you see at the beginning of a piece of music right after the clef sign, and right before the time signature.

Here is a key signature with five sharps (#), which is typically used for B Major:

Notice how the five sharps are right in between the clef and the time signature. However, this key signature could also be used to indicate a key of G# minor. There is always a major and minor key for each key signature. These are called relative keys, and they are always three semitones apart (the minor key is three semitones below the relative major key).

To figure a key out for a song that you are learning to play, first check the key signature, and then try to find the tonic note or chord. Sometimes songs can change keys, or modulate, so be on the lookout for those.

The first one is a Bach piano sonata in D minor. You can tell because the first notes played are a D minor chord – D, F, A.
This one is a Mozart piano sonata in F Major. The right hand melody starts by playing F – A – C, which makes an F Major chord, and the left hand accompanies it with the same notes.