Nicely into the I chord and helps the listener realize the song is going to repeat. This is very common when you want to repeat the form. The next example changes the last measure from a I7 to a V7. I kept it simple by showing whole notes, but I would try quarter ntoes. This next example is the most basic form of the 12 bar blues in the key of C using the chords C7, F7, and G7. The basic 12 bar blues consists of the following: So in the key of C: I7 = C7, IV7 = F7, V7 = G7. The C major scale consists of the following notes: C, D, E, F, G, A, B. Since these are all dominant chords they have some dissonant notes that are not in the keyįor those who don’t know, the roman numerals represent the degree of the major scale. The 12 bar blues form consists of 12 bars or measures.