Who here has ever composed constrained writing? It's very interesting, you just decide to restrict yourself before you compose a piece. A Common constrained composing technique is only using notes in the key (i.e. A piece in D major could only use D E F# G A B and C#). Another is deciding that you'll play every note in the chromatic scale in once piece. There are also rhythmic contraints, like playing the same rhythm on a hand throughout a longish piece, or never writing note values smaller than an eighth note.
Scriabin used composition constrained to only the left hand, and minamalist composers have limited themselves to only using 5ths and octaves in a composition.
Here is an example of constrained writing that I put down last year. The rules for this piece were this:
The melody must be played on the left hand
The right hand must never stray from a particular eighth note rhythm (in pitch, it goes up up up down in groups of 4 at all times)
The piece must use at least three different keys (it uses several passing keys, but settles in E flat, E flat minor and C minor)
Every note in the Chromatic scale must be used at some point
The results from this kind of limitation can be very interesting, as they create rich, and particular melodies, that must be well thought out and planned before composition.
Hope you guys find this interesting:
http://media.putfile.com/ODonnell--Prel ... Flat-Major