Keys and Key Signatures
The key describes the note around which a piece of music is built. When a song consists of notes from a particular scale, it is said to be written in the key which has the same notes as that scale. The key signature is written at the start of each line of music, just after the clef.
The number of sharps or flats in any key signature depends on the number of sharps or flats in the corresponding major scale. The major scales and key signatures for the keys of F and G are shown below. Without sharps and flats, these scales would not contain the correct pattern of tones and semitones which gives the major scale its distinctive sound.
G Major Scale
Key Signature of G Major
The G major scale contains one sharp, F#, therefore the key signature for the key of G major contains one sharp, F#.
F Major Scale
Key Signature of F Major
The F major scale contains one flat, Bb, therefore the key signature for the key of F major contains one flat, Bb.
Some scales contain sharps while others contain flats because there has to be a separate letter name for each note in the scale. E.g. the G major scale contains F# instead of Gb even though these two notes are identical in sound. If Gb was used, the scale would contain two notes with the letter name G and no note with the letter name F. In the key of F major, the note Bb is chosen instead of A# for the same reason. If A# was used, the scale would contain two notes with the letter name A and no note with the letter name B.
The charts on the following page contain the key signatures of all the major scales used in music, along with the number of sharps or flats contained in each key. Because there are 12 notes used in music, this means there are 12 possible starting notes for major scales (including sharps and flats). Note that some of the keys will have sharps or flats in their name, e.g. F# major, Bb major, Eb major, etc. Keys which contain sharps are called sharp keys and keys which contain flats are called flat keys.
The key signatures for all the major scales that contain sharps are:
The sharp key signatures are summarised in the table below.
Written below are the key signatures for all the major scales that contain flats.
The flat key signatures are summarised in the table below.
*An interval is the distance between two notes. Intervals are named by the number of letters they are apart, e.g. C to G is a fifth. Intervals are discussed in detail in lesson 22.
