With the exception of C major and A minor, all keys must use one ore more accidentials. To facilitate reading, the sharps and flats needed for a particular key appear at the beginning of each staff, giving us the key signature.
| Key | Major | Minor | ||
| Keys requiring sharps are found in intervals
of consecutive upward 5ths. Each successive sharp key
adds another sharp to the key signature. This new sharp is always
the leading tone of the new key. Keys requiring flats are found in intervals of consecutive downward 5ths. Each successive flat key adds another flat to the key signature. This new sharp is always the 4th of the new key. A minor key has the same key signature as the major key which lies a minor 3rd above it. Minor and major with the same amount of sharps or flats are named 'parallel keys'. |
0# / 0b | C | A | |
| 1# | G | E | ||
| 2# | D | B | ||
| 3# | A | F# | ||
| 4# | E | C# | ||
| 5# | B | G# | ||
| 6# | F# | D# | Two keys which sound the same but are spelled differently are termed 'enharmonic'. | |
| 6b | Gb | Eb | ||
| 5b | Db | Bb | ||
| 4b | Ab | F | ||
| 3b | Eb | C | ||
| 2b | Bb | G | ||
| 1b | F | D |
All the keys and their enharmonic relationships can de shown on the 'circle of fifth' or simply 'The Cycle', an arrangement of the 12 keys so that the number of sharps in the key signature encreases clockwise, and the number of flats counterclockwise.