An open chord leans on open strings, so each open grip belongs to one key. To play a blues in any key you need grips that move, and two shapes are enough: the open E7 and the open A7, moved up the neck.
A7, D7 and E7 in one place
A7 as the E7 shape at fret 5, D7 as the A7 shape at fret 5 and E7 as the A7 shape at fret 7.
A7 is the open E7 shape moved up five frets. D7 is the open A7 shape moved up five frets, and E7 is the same shape moved up seven frets. Your first finger lies across the strings at the marked fret, doing the job the nut does for an open chord. All three sit between frets five and nine.
Why the IV is straight across
Look at where the roots are. A7 has its root on the sixth string at the fifth fret, and D7 has its root on the fifth string at the same fret. That is not a coincidence. The fifth string is tuned a fourth above the sixth, and the IV of a key is a fourth above the I, so the IV is always straight across from it. The V is a whole step above the IV, which puts it two frets higher on the same string.
So the three chords stay close together. Find the I on the sixth string, and the IV is straight across on the fifth string, with the V two frets above it. When you change key, the three move together.
The same twelve bars in C
To play the blues in C, find C on the sixth string. It is at the eighth fret, so C7 is the E7 shape there, F7 is straight across on the fifth string, and G7 is two frets above F7.
C7, F7 and G7 in one place
C7 as the E7 shape at fret 8, F7 as the A7 shape at fret 8 and G7 as the A7 shape at fret 10.
C7 is the open E7 shape moved up eight frets. F7 is the open A7 shape moved up eight frets, and G7 is the same shape moved up ten frets. Your first finger lies across the strings at the marked fret, doing the job the nut does for an open chord. All three sit between frets eight and twelve.
The twelve-bar blues, in C
The twelve-bar blues in C: C7, C7, C7, C7, F7, F7, C7, C7, G7, F7, C7, G7.
The numerals under each chord are the same as in A. Only the letters have changed, because a numeral names a chord by its distance from the key rather than by its note.
This is why players talk about a blues in numerals. When someone calls a blues in C, everyone knows it means C7, F7 and G7, and a guitarist knows the three grips sit around the eighth fret.
This lesson was drafted with the help of AI, so it may contain a mistake. Its diagrams are drawn by Everyfret’s own software. How Everyfret is made