Twelve bar blues has a rigidly defined chord progression: I-I-I-I-IV-IV-I-I-V-IV-I-I. Repeat ad nauseam. The result is that all such songs have a tendency to sound alike. Note that it doesn't take much deviation from the formula to make a song enjoyable: the Pink Floyd songs "Money" (from Dark Side of the Moon) and "Dogs of War" (from A Momentary Lapse of Reason) are based on that same chord progression but have deviations as simple as changes in meter that are enough to make both songs enjoyable.
In principle, it is quite simple to write a twelve-tone piece. Start with the twelve notes of the Western chromatic scale arranged in some initially arbitrary order. Once that order is fixed, the following transformations are allowed:
- Inversion. Where the original sequence goes up (down) by n semitones, the new sequence goes down (up) by the same number of semitones.
- Retrogression. Play it backwards. (The people who were looking for hidden messages by playing songs backwards were looking in completely the wrong place.)
- Inverted retrogression. Do both of the above transformations.
- Transposition. Take the original sequence, or the result of any of the above transformations, and shift every note by the same number of semitones.
In most cases, these transformations will give you a total of 48 sequences. Your mission, should you choose to accept it, is to use all 48 sequences in something that actually sounds like music and not just mind games. I don't know of anyone who has succeeded; there has not been the equivalent of the Well-Tempered Klavier for twelve-tone rows. Again, it's not that I dislike 20th century concert hall music; on the contrary, I count Aaron Copland, Gustav Holst, and Percy Grainger. The difference is that these composers connect with the listener, in ways that practitioners of twelve-tone music like Arnold Schoenberg do not.