Since the 12 Bar Blues is the most common progression in Blues music, it is worth looking at it in more detail. There are usually three different chords used. Each of these chords relates to one basic key. The key is the central note around which a piece of music is based. For example, a piece of music in the key of A would be made up of notes from the A major scale. Chords can be built from any notes of the scale. In Blues, the most common chords are those built on notes 1, 4 and 5 of the major scale. So in the key of A, these chords would be A, D and E.