How much of someone else’s copyright material can you legally use without getting permission? Notice the question is not whether or not you are going to get sued, which is likely the more important question. Unfortunately, no law or attorney can answer that question. Whether you are going to get sued depends much more on the motivations, as well as the relative strengths of the parties. Is the entity from whom you are taking the copyright work an 800lb gorilla run by the guy with an itchy suing finger you fired three years ago? If so, a detailed analysis of the esoteric legalities of fair use under United States Copyright Law is kind of a moot point. You are going to get sued. And since you likely do not have the $30K+ to fight the case, you are likely going to lose or settle for far less than what might otherwise be considered “fair.”
Now, once you have done the am-I-going-to-get-sued analysis, and are satisfied the copyright owner is passive or at least not overly litigious toward you, how do you determine what constitutes “fair use” of the copyright work? Can you use a quote from someone else in your own work? Maybe.
In some situations it is permissible to use limited portions of a copyright work, including quotes, for purposes such as commentary, news reporting, scholarly reports. This is particularly true for current news stories & historical analysis (to promote accuracy). The quoted material, however, must not be unreasonably large and must not destroy the market for the original work (quoting the salacious portions of Monica Lewinsky’s memoirs).
Be aware that courts rarely uphold a claim of “fair use” in a for-profit, commercial context unless the use is directly tied to parody, news or critical commentary. In determining whether your copying constitutes “fair use” the courts will look at:
1) The purpose and character of your work-Are you making money from the copies?
2) Nature of copyrighted work-Is it a form book meant to be copied?
3) Amount of work taken-Are you taking 90% of the work or 2%?
4) Economic impact of taking-Are you taking the 2% that makes people want to buy the original (Lewinsky passages)?
In determining whether a use is a fair use, courts weigh all of these factors, along with additional factors indicating why or why not your use might be allowable under copyright law. If you are copying 1% of the non-critical portions of a form book for your own personal use, you are okay. If you are selling 98% complete copies of the The DaVinci Code, you are in trouble. For anything in between, it is best to either consult your copyright attorney for advice or stick with copying works already in the public domain.