Many blues songs are based on a 12 bar chord progression. If you can get familiar with this sequence, you can accompany many blues musicians and soloists. When playing in any key, you can figure out the three chords you’ll use most by counting up the alphabet to chords 1, 4 and 5. In other words, consider the key of G. Your root cord is G, which will be number 1. Counting up the alphabet, 2 equals A, 3 equals B, 4 equals C, 5 equals D, 6 equals E, and 7 equals F-sharp. The three major chords you need are numbers 1, 4, and 5 – or G, C, and D.
Try this with another key – perhaps D. D, E, F-sharp, G, A, B, C-sharp, D are the order of notes, and if you see the notes in positions 1, 4, and 5, you’ll see D, G, and A, which are indeed the three basic chords we use. By the way, the chords in positions 2, 3, and 6 we will tend to use as minor chords in that particular key. But you won’t use minors in a 12 bar blues progression. When these chords are referenced in articles, they are often designated by Roman numeral, or chords I, IV, and V.
Now for the blues guitar lesson. To make your playing really sound bluesy, you can play those chords I, IV, and V in their 7th form. The blues progression that is used so frequently consists of repeating the chords in this order: I, I. I, I, IV, IV, I, I, V, IV, I, V, and then back to the beginning. This progression can go on indefinitely, but sometime or other everyone will have to leave off that V at the end and just play another I to bring the thing to a close.
So what does this all mean? Each note in the above sequence bets a four beat measure. Lets take the key of A as an example. You will play A-7 for four measures, or 16 beats, then switch to D-7. Play it for two measures, or 8 beats, and then switch back to A-7 for two measures (8 beats.) Then go to E-7 for four beats, D-7 for four beats, A-7 for four beats, and E-7 for four beats, and then start over to repeat the whole twelve measures.
If you search online, you can find blues guitar lessons that will give you a free MIDI file of these chords to play along with in various strumming and rhythm patterns. The twelve bar blues progression is a basic fact of life in the different forms of popular music, and turns up in rock and country music as well as in blues and jazz. You’ll feel like a pro when you master this simple progression.