The typical 12-Bar blues format is, of course, made up of 12 measures. In addition, it features predominantly only three chords: the I7 , IV7 , and V7.
You can also divide the format into different sections (or as I call “rows” when visually represented on a graph or piece of sheet music) based on when the emphasis is, as well as where you begin a new lyric line to the verses:

Today, I am going to be giving you a list of examples to ways you can alter the middle section of a 12-Bar blues:

Notice the similarities and differences between them. In addition, see how the last chord of the “row” leads into the last 4 measures. Some of them might work well together while others may not.
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