Eight bar blues
An eight bar blues is a typical blues chord progression, taking eight 4/4 bars to the verse.
A basic example of the progression would look like this, using T to indicate the tonic, S for the subdominant, and D for the dominant, and representing one chord per beat:
T T S S T T T T S S S S T T T T T T T T S S S S T T D D T T T T
(The same chord progression can also be called a sixteen-bar blues, if each symbol above is taken to be a half note in 2/2 or 4/4 time -- blues has not traditionally been associated with notation, so its form becomes a bit slippery when written down.)
Many variations are possible. For instance, seventh chords are often used just before a change, and more changes can be added. A more complicated example might look like this, where "7" indicates a seventh chord:
T T S7 S7 T T T7 T7 S S S7 S7 T T T T T T T7 T7 S S S7 S7 T T D7 D7 T T T D7
When the last bar contains the dominant, that bar can be called a turnaround.
Finally, here is an example showing the pattern in the key of D, and how it fits with the lyrics of a given verse. One chord symbol is used per beat, with "-" representing the continuation of the previous chord:
D -
Woke up this morning with the
G - D - D7 -
blues down in my soul
G -
Woke up this morning with the
G7 - D - - -
blues down in my soul
D - D7 -
Woke up this morning with the blues in my soul
G -
Saying "My baby gone and left me, got a
G7 -
heart black as coal"
D -
Woke up this morning with the
A A7 D - A7 -
blues down in my soul
Some well known eight bar blues are "Ain't Nobody's Business," "Cherry Red," and "(Romancing) In The Dark."
See also: twelve bar blues, chord progression.