Using the rhymed couplet, what form did the typical 12 bar blues take on?

In its most basic form (see the list of exceptions below) most 12-bar blues songs will comply with the rule "A, A, B" - i.e. Line A is repeated, then a different line closes the verse.

For example, from "St. Louis Blues":

I hate to see that evening sun go down,
I hate to see that evening sun go down,
It makes me think I'm on my last go-round.

Hence, a blues verse usually has three lines over twelve measures, or bars. The root (one) chord of a major scale is played during the first line for the first four measures, then the four chord is played for measures five and six, and the one chord is played again for measures seven and eight. The last line is different, with the five chord played for measures nine and ten and the one chord played again for measures eleven and twelve.

A verse in a blues song (again, see the exceptions listed!) has three lines of lyrics; the first and second lines are the same (with different chords) while the third line is different. This structure is the classic vocal form of the twelve-bar blues.

A list of exceptions to the rule:

http://en.wikipedia.org/wiki/Twelve_bar_...

Useful to read:

http://www.soundme.com/eng/blues/blue01....

http://www.12bar.de/rhythm.php

Hey Bowzer... those were some great links... thanks.