The cycle of fifths - An aid to II V I (2 5 1)
The good old cycle of fifths (or fourths!) has many uses in music, not the least of which, of course, is to make sense of the keys and key signatures we use in music.
If you look at a diagram of the cycle of fifths you'll see that if we start at the top in the key of C, that key has no sharps or flats, as we go right to G, that has 1#, D has 2#, A has3# and so on.
Going left, we go into the flat territory, F has 1b, Bb has 2b, Eb has 3b etc.
A very useful aid memoire. Note when we get to 6b, its the same key as 6#, but of course written differently.
Jazzers (and classical performers) often call the keys by the number of flats or sharps in that key as it avoids misinterpretation when calling across a stage "What key is this in? D or E, I can't quite hear" You can then say, 2 or 4 sharps to make it clear.
Also, many musicians hold up a number of fingers to indicate the key, three fingers up mean A, three fingers down Eb. (Be careful when indicating the key of D!)
What about the II V I sequence?
In previous posts we looked at the chords of the major scale, and we found that chord II will be a minor seventh chord, chord V a dominant seventh and chord I a major seventh chord (using four note chords).
In C that would be Dmin7, G7 and Cmaj7 (D minor seventh, G dominant seventh (or just G7) and C major seventh).
This II V I, or a lot of the time just a II V is found all over the music we play in jazz, especially the 'standards'. When playing those three chords in sequence, you'll hear what I mean. Look at chord charts, or lead sheets of those pieces, and you'll see what I mean, the sequences will be everywhere!
Don't forget that there are twelve keys altogether, so how do you remember them all?
Look at the cycle of fifths, they are all there!
D G C (going backwards from D) is there. The II chord is D min7 The V is G7 and the I is C.
Lets say you want the II V I in Eb, That will be Fmin7, Bb7 and Ebmaj7.
That will be Bmin7, E7 and Amaj7.
All this will be made much clearer if you can go on a Jazz Workshop where everyone will be using the II V I sequence all over the place.