Before and during composing it is very interesting to set up limitations of some sort. In fact it is very hard to compose if you don´t limit yourself in any way; if you have all the instruments and all the musical possibilies actually available to you, where do you start? Bach of course was a master in composing under strictly limited conditions, e g composing a fugue.  This also relates to a previous post about choice or chance (where I promised to write more about its subject). It can be very interesting to use chance to set up ones limitations. Cage were, as I wrote in the previous post, very interested in chance. He was also very interested in natural or accidental sounds and their relation to "music", and used chance to investigate that relation. I am inclined to be more interested in using actual choices to set up the limitations - to use experience and judgment. I will get back to this (again) and write more about different limitations.