Examples of fair use include using quotations from the work, criticizing the work, or creating a parady of the work. Using a copyrighted work for the above purposes is not considered illegal infringement.
There is no clear definition of transformative purposes, as it varies from case to case and judge to judge. US law makers must keep a delicate balance of fair use as to not limit or prevent free speech, while alternately protecting the rights of the copyright owner. Without fair use, premission would be needed to properly review any work. If this were the case then authors and musicians could effectivly stiffle any negative reviews or comments about their work.
The implementation of fair use can fall into two categories: comment and parady.
If you are reviewing a novel or a song, fair use allows you to use direct quotes from the work to fully convey your analysis. In the case of Wright v. Warner Books, Inc., Richard Wright sued Warner Books for quoting six unpublished letters and ten unpublished journal entries. Though they were not published, Wright still owned the legal copyright of his work. The court decided, however, that because less than one percent of the letters were copied and because their purpose was informational, that Warner Books was implementing fair use.
A parody is any work that makes fun of another work. The work being ridiculed is often well known, and the creator is unlikely to agree to his work being ridiculed. An example is when Saturday Night Live parodied "I love New York" and transformed it into "I love Sodom." In the court case Elsmere Music, Inc. v. National Broadcasting Co., the ruling was the only the words, "I love" and four musical notes were copied and therefore SNL was excersizing fair use.
