Collaborative play writing

Plans for the project

The idea behind this project is to write a play, starting with a monologue and gradually re-writing it into a dialogue. One new character will be added with each re-write and, in this manner the script will eventually be fleshed out into a full play. So the key would be to start with a really good monologue. Here is a point to ponder, however: if we use a pre-existing, copyrighted monologue as a starting point, will we be violating the copyright? Since the final product will be vastly different from the original text, this may be permissable, but on the other hand, the original text may still be there - word for word - but simply spread out throughout the script. Also, is the copyright on the actual text alone? Or does it include the idea behind the text as well (ie. would paraphrasing the original piece still be violating the copyright)?

Do you have some specific examples of "pre-existing, copyrighted monologue" that you might want to use?